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The mean-field approximation based on the Gibbs-Bogoliubov inequality and Monte Carlo simulations based on the Metropolis method in the Blume–Emery–Griffiths model were used to successfully examine a hexagonal Ising nanowire with spin-1. It was found that the model displays fascinating phase diagrams in various planes of interest by using both methods. The investigation of magnetic hysteresis cycles also exhibits interesting properties. The model not only presents first- and second-order phase transition lines, but also the tricritical and isolated critical points, multi-compensation temperatures, and magnetic hysteresis behavior with one to eight cycles. • The mean-field approximation based on the Gibbs-Bogoliubov inequality is applied. • The Monte Carlo simulations based on the Metropolis method is employed. • Spin-1 Blume–Emery–Griffiths model for hexagonal Ising nanowire is investigated. • First- and second-order transitions, tricritical and isolated critical points are found. • Multi-compensation and magnetic hysteresis with one to eight cycles are observed. [ABSTRACT FROM AUTHOR]

We report here the studies of structural and magnetic properties of two equiatomic quaternary Heusler alloys CoCrVZ (Z = Al, Ga). Both the alloys crystallize in LiMgPdSn type crystal structure (space group #216) with B2 (CoCrVAl) and A2 (CoCrVGa) type anti-site disorder between elemental sites. Intended stoichiometry was confirmed from the compositional analysis. The temperature dependence of dc magnetic susceptibility and the low temperature moment values show a nearly compensating ferrimagnetic behaviour at low temperatures for both the alloys. The inverse of dc magnetic susceptibility starts to deviate from the Curie–Weiss law below 220 K and 164 K for the alloys containing Al and Ga respectively. The Arrott plots confirms the absence of long range order down to 2 K. Further analysis of the dc and ac susceptibility shows that the observed behaviour is due to the presence of Griffiths like phase in these alloys. • Systematic study shows that CoCrVZ (Z = Al, Ga) Heusler alloys crystallize in LiMgPdSn type structure (space group #216) with 50% B2 (CoCrVAl) and 25% A2 (CoCrVGa) type anti-site disorders. • The presence of disorder leads to the reduction of magnetic moment and a nearly compensated ferrimagnetic behaviour at low temperatures. • The presence of Griffiths like phase is inferred for both the alloys. [ABSTRACT FROM AUTHOR]

• The Ta/GdFeCo/Ta heterostructures are utilized to achieve a spin–orbit torque-driven multistate magnetization switching. • The switching ratio is up to 47.7% and the β DL and β FL are estimated as 85.64 Oe/(107 A/cm−2) and 35.05 Oe/(107 A/cm−2), respectively. • The findings establish that a stable four-resistor state exists, proofing multilevel memory behaviors and synaptic plasticity under current drive. • Neuromorphic computing built from this SOT device can perform unsupervised handwritten digit recognition with an accuracy of 92.25%. Neuromorphic computation of ferrimagnetic materials as artificial synapses is essential for the development of ultra-low power spintronic devices. Here, Ta/GdFeCo/Ta heterostructures are utilized to achieve a spin–orbit torque-driven multistate magnetization switching, complying with the requirements of neuromorphic computation. For Ta/GdFeCo/Ta device, the switching ratio is up to 47.7 % when the critical current density value is 1.26 × 107 A/cm2. Moreover, the β DL and β FL are estimated as 85.64 Oe/(107 A/cm−2) and 35.05 Oe/(107 A/cm−2), respectively. Subsequently, the findings establish that a stable four-resistor state exists, proofing multilevel memory behaviors and synaptic plasticity under current drive. It is further demonstrated that neuromorphic computing built from this SOT device can perform unsupervised handwritten digit recognition with an accuracy of 92.25 %. This research highlights the potential of SOT-driven multi-energy stabilized residual states for neuromorphic computing and multi-energy storage in the future. [ABSTRACT FROM AUTHOR]

• Gd-content gradients influence PMA in both "+δ" and "−δ" samples. • "+δ" has lower H C due to closer T comp , suggesting different Gd-content. • Reversal of AHE loop near T comp indicates sublattice dominance shift. • Decrease in H SF suggests weakened exchange interaction near T comp. • Strong ΔR XY at ± 4 kOe and ± 30 kOe for "−δ" indicates enhanced PMA. Ferrimagnetic rare-earth (RE) – transition-metal (TM) alloys are considered small ferromagnets with antiferromagnetic exchange in sublattices, which makes them a preferable choice for future ultrafast memory-related applications. Here, we explore the magnetic properties of two GdFeCo thin films with tailored vertical composition gradients, achieved by gradually varying Gd concentration across the film thickness. The temperature-dependent magnetic behavior of these films is investigated using anomalous Hall effect (AHE) measurements and SQUID magnetometry. Both films exhibit perpendicular magnetic anisotropy with distinct coercivities, indicating variations in their magnetic properties. The films show RE-dominant behavior at 300 K. Moreover, for the positive composition gradient (+δ) film, the compensation temperature is around 350 K, while the film with a negative gradient (−δ) exhibits a compensation temperature above 400 K. Furthermore, the spin-flop behavior and AHE sign reversal provide insights into the sublattice dominance and exchange interactions within the films. The magnitude of ΔR XY (the difference in AHE resistance at different magnetic fields) is shown to be sensitive to the composition gradient, indicating stronger perpendicular magnetic anisotropy for the "−δ" sample. This study demonstrates the potential of composition engineering to tailor the magnetic characteristics of ferrimagnetic materials for specific spintronics applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel porous aggregates of multi-element doped Fe 3 O 4 /(Fe,Co, Ni, Cu) alloys (DF/alloys) composite with magnetic/magnetic heterostructure was prepared. • Ferrimagnetic spinel compounding with ferromagnetic four element alloys enlarged the M s and helped to break the Snoek′s limit. • The abundant defects and heterogeneous interfaces of the DF/alloys composite enhanced its dipole polarization and interfacial polarization and optimized impedance matching. • The maximum effective absorption bandwidth (EAB max) and minimum reflection loss (RL min) were 6.4 GHz and −49.3 dB with a thickness of 2.0 mm. Pure magnetic materials always exhibit mediocre microwave absorption performance due to the poor impedance matching and negligible dielectric loss capability. In this study, a novel porous aggregates of multi-element doped Fe 3 O 4 /(Fe, Co, Ni, Cu) alloys (denoted as DF/alloys) composite which is composed of magnetic/magnetic heterostructure with excellent microwave absorption performance were prepared. By reducing part of the ferrimagnetic spinel into ferromagnetic alloy, the saturation magnetization M s was enlarged which is beneficial to exceeding the Snoek′s limit, and the magnetic loss capability was further enhanced significantly. Furthermore, the abundant heterogeneous interfaces in the DF/alloys composites have greatly improved the dielectric loss capability and balanced the complex permittivity and the complex permeability, and achieved superior impedance matching of the magnetic/magnetic heterogeneous DF/alloys composites. When the loading ratio (DF/alloys to paraffin mass ratio) was only 30 wt%, the widest effective absorption bandwidth (EAB) reached 5.58 GHz (3.2 mm). when the loading ratio was up to 50 wt%, the widest EAB (6.4 GHz) was achieved at 2.0 mm and the minimum reflection loss (RL min) reached −49.3 dB at 4.15 GHz. As microwave absorption materials, the DF/alloys composites are extremely promising and competitive. [ABSTRACT FROM AUTHOR]

• YFeO 3 have been studied with GGA and GGA+U reveal a semi-conductor and an Antiferromagnetic type-G behavior. • Magnetic anisotropy results for both approximations show that easy axis magnetization for YFeO 3 is along the c-axis. • Evaluation of the electric polarization and the magnetic transition temperature of the orthorhombic YFeO 3 has done. In this study, we have thoroughly investigated the electronic, magnetic, and electrical properties of yttrium orthoferrite using density functional theory (DFT) within the generalized gradient approximation (GGA) and the (GGA + U) approach, which incorporates the Hubbard term (U). Both approximations consistently reveal a semiconductor behavior and an antiferromagnetic behavior of type-G between the iron (Fe) ions. To delve deeper into the magnetic interactions within YFeO 3 , we have proposed a physical model. This model allows us to calculate the magnetic exchange coupling and magnetic anisotropy parameters through DFT calculations. Additionally, we have conducted computations to determine the electric polarization. Our results have shown that the electric polarization in YFeO 3 is exclusively derived from electronic polarization. We have also explored the relationship between the direction of electric polarization and the easy-axis magnetization. In our investigation, we found that both the electric polarization and easy-axis magnetization align along the c-axis in both approximations. Furthermore, we have examined the influence of the Hubbard term on the direction of polarization. To assess the magnetic temperature transition, we employed Monte Carlo simulations using the Ising model. The critical temperature, denoted as T N , obtained with the GGA approximation is found to be 726.66 K. Remarkably, this value closely matches the experimental critical temperature when compared to the critical temperature obtained with the GGA + U approximation. [ABSTRACT FROM AUTHOR]

ZrMnSi and HfMnSi half Heusler alloys with magnetic ground state are investigated through density functional theory. The different exchange–correlation functionals (GGA, LDA, PBESol and WC) are used to study these alloys. The equilibrium lattice constants and corresponding ground state energies are calculated using these four approximation methods. From GGA functional, the obtained band gap for ZrMnSi is 1.268 eV and HfMnSi is 1.311 eV. The reported alloys are predicted to be half metals from different potentials, where those alloys show semiconductor character in minority spin channel and also exhibit metallic character in majority spin channel. The studied alloys are mechanically stable and ductile in nature. The total magnetic moment of −3 μ B is obtained in the reported ferrimagnetic alloys. The obtained thermoelectric figure of merit for ZrMnSi and HfMnSi is 0.46 at 1200 K and 0.31 at 1200 K respectively, it shows that these alloys are the potential candidates for waste heat recovery application, and they are also useful for spin flip device application. • We studied the spintronic and thermoelectric properties of the ZrMnSi and HfMnSi. • We predicted the semiconductor character of the Heusler alloys ZrMnSi and HfMnSi. • For both of the Heusler alloys ZrMnSi and HfMnSi the band gap value is 1.29 eV. • The ZT is 0.46 and 0.31 for ZrMnSi and HfMnSi at 1200 K. • ZrMnSi and HfMnSi are best suit for spintronic and thermoelectric applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single phase spinel structure was revealed with crystallite size of 10.94–25.44 nm. • The microstructural investigations disclosed average particle size of ≈ 26.87 nm. • Ferrimagnetic nature of Ni-Co-Pr nanoparticles was revealed in magnetic studies. • ε ′ and ε ″ followed decreasing tendency with increase in applied field frequency. • These ferrites have potential uses in high density memory and high frequency devices. Praseodymium (Pr3+) substituted Nickel-Cobalt ferrites with composition Ni 0.3 Co 0.7 Pr x Fe 2-x O 4 and concentration (x = 0.00, 0.05, 0.10, 0.15, 0.20) were synthesized via sol–gel approach. The crystallite size was lying in 10.94–25.44 nm range having decreasing tendency and lattice constant was varying between 8.30 and 8.39 Å. Two absorption bands were seen in infrared spectroscopy around 550 cm−1 and 430 cm−1, representing spinel structure. Morphological analysis revealed particle size of ≈ 26.87 nm. Magnetic investigations disclosed decreasing trend in saturation magnetization (M s), retentivity (M r) and coercivity (H c) and were determined in 19.77–50.75 emu/g, 0.77–19.48 emu/g, and 87.23–943.27 Oe range, respectively. Dielectric parameters showed decreasing trend with increase in frequency. Dielectric constant and loss were decreased from 3.64 to 2.59 and 0.502–0.420 for Pr3+ concentration × = 0.00–0.20 at 0.5 GHz, respectively. AC conductivity showed elevation with increasing applied frequency. These reported magneto-dielectric features suggest possible use of material in high density memory and high frequency devices. [ABSTRACT FROM AUTHOR]

Due to interesting properties such as perpendicular magnetic anisotropy (PMA), ferrimagnetism, etc., rare earth-transition metal(RE-TM) alloys attract considerable attention in ultrafast and terahertz spintronics applications. The magnetic properties of RE-TM alloys strongly depend on their composition and vary with temperature. Here, we model crystallographically amorphous ferrimagnetic TbCo using atomistic spin dynamics(ASD) simulations to study their temperature dependence on magnetic properties by varying the compositions. In this study, we investigate the temperature dependence of magnetisation, uniaxial anisotropy, and coercivity values of amorphous Tb x Co 100 − x for the composition range Tb 18 Co 82 to Tb 36 Co 64. The monte carlo method is used to calculate the temperature dependence of magnetisation and calculate the magnetisation compensation temperature(T M) and curie temperature(T c) values for different compositions. The temperature dependence of uniaxial anisotropy is calculated from the angular dependence of free energy curves calculated at different temperatures using constrained monte carlo methods. Further, we evaluate the temperature dependence of coercivity values by calculating the magnetic hysteresis at different temperatures using the LLG Heun method. The results show the magnetic properties of amorphous TbCo can be easily tuned by varying their composition and have a strong temperature dependence. These highly tunable magnetic properties make them promising candidates for spintronics applications. [Display omitted] • RE-TM alloy thin films are interesting for ultrafast and terahertz spintronics applications. • RE-TM alloys are known for their intrinsic PMA, Ferrimagnetism and compensation temperatures. • The temperature dependence of M s , K u and H c of amorphous TbCo is studied using ASD simulations. • Magnetic properties of RE-TM alloys strongly depend on their temperature and composition. [ABSTRACT FROM AUTHOR]

• Ferrimagnetic mixed spin (3/2,1) Ising for zigzag and armchair graphene-like nanoribbons (GNRs) is investigated using the finite cluster approximation FCA. • Transition reentrance is revealed for both GNRs for lower J co strength. • Double compensation points are identified for the armchair GNR under the effect of the shell crystal field. • The core crystal field may lead for both zigzag and armchair GNRs, to a tricritical behavior. Graphene-like nanoribbon structures (GNRs) in which singular magnetic properties emerge because of the graphene-cutting process, may offer unique opportunities for future technological development such as spintronics. Using the finite cluster approximation, research has been implemented on some magnetic and critical characteristics of a mixed spin-3/2 and spin-1 Ising ferrimagnetic graphene-like nanoribbon with two typical edges, namely armchair, and zigzag. We investigate the influences of such aspects as crystal fields, exchange couplings, and temperature on phase diagrams and magnetizations. Tricritical as well as compensation behaviors have been demonstrated under the effect of the above physical parameters. In particular, only armchair GNR may exhibit double compensation points. Meanwhile, an unexpected reentrant transition has been discovered for both GNRs, which is mainly due to the finite size effect. [ABSTRACT FROM AUTHOR]

A model for the description of atomic and magnetic ordering in Ni Mn Al shape memory alloys is presented. The parameters characterizing the energies of the chemical and magnetic interactions were obtained from fitting to experimental data. Monte Carlo simulations based on this model correctly reproduces the critical B 2 ↔ L 2 1 ordering temperatures as a function of composition for three pseudobinary composition lines, as well as the nature of the low temperature magnetic transition. A ferromagnetic configuration is predicted for alloys in the stable L 2 1 structure, whereas an antiferromagnetic state is obtained for metastably retained B 2 order; this is in agreement with experimental observations. It is verified that atomic ordering is strongly dominated by the interactions between Ni and Al atoms in nearest neighbours. As a consequence, the formation of B 2 order can delay the stabilization of the L 2 1 configuration at low temperatures. Since the magnetic interactions change sign with the Mn–Mn distance, the type of stable magnetic configuration depends on atomic ordering. • Atomic and magnetic ordering in Ni–Mn–Al alloys is studied by means of Monte Carlo simulations. • The critical B2-L2 1 temperatures are correctly reproduced for different compositions. • For L2 1 (B2) order a ferromagnetic (antiferromagnetic) state develops at low temperatures. • Variation of the order degree with temperature and composition is studied. [ABSTRACT FROM AUTHOR]

We studied the compensation behavior, the reentrant phenomena characterizing first order phase transitions, and the exchange bias effect manifested by asymmetric hysteresis loops for a core–shell nanotube with mixed spin (1 , 3 / 2) by combining both the effective field theory and the probability distribution technique. Since our system is intended to be disordered on the shell, a uniform distribution for the exchange anisotropy proposed. Among the interesting results are the compensation behavior in the ideal and disordered cases, where we noticed a critical behavior manifested by total magnetization persistence, the compensation behavior accompanied by the reentrant phenomena, as well as the multi-loops behavior, exchange bias effect, and magnetic susceptibility. Internal energy, Helmholtz free energy, and double peak specific heat are also used to invoke the energetic aspect. • Ferrimagnetic systems' magnetic properties. • Disordered magnetic systems. • Reentrant magnetic phenomena. • Multi-hysteresis loops and hysteresis loops. • First order phase transition and compensation temperature. [ABSTRACT FROM AUTHOR]

• Coexistence of cubic and tetragonal phases in quaternary Heusler alloys, CuCoCrAl and CuFeCrAl, revealed by XRD and neutron diffraction data. • Different magnetic states of the cubic and tetragonal phases, leading to an overall ferrimagnetic behaviour in both the alloys. • Observation of metallic character with weak localization. We have investigated two equiatomic quaternary Heusler alloys CuTCrAl (T = Co and Fe) theoretically and experimentally. Both the alloys have been characterized using X-ray Diffraction (XRD) and neutron powder diffraction (NPD). Refined results of XRD and NPD show the presence of A2/B2 type disorder with the coexistence of mixed-phase of cubic and tetragonal symmetries in CuFeCrAl and CuCoCrAl. NPD magnetic structure refinement indicates the presence of ferrimagnetism with a very low moment at low temperatures. DC magnetization results reveal the presence of weak itinerant ferromagnetic behaviour. Temperature dependence resistivity reflects the metallic character with the presence of weak localization at low temperatures. The coexistence of cubic/tetragonal and ferrimagnetism along with metallic nature in a single system is quite rare, revealing the potential of these alloys for multifarious applications. [ABSTRACT FROM AUTHOR]

The magnetic response of an identical magnetic nanoparticles (MNP) system to a rotating external field (RMF) is studied via Monte Carlo simulations. The field of amplitude H 0 and frequency ω , was applied in the y − z plane rotating clockwise. The energy was modeled by the Stoner–Wohlfarth scheme for fixed or random orientations of the anisotropy, and is in contact with a thermal bath at a temperature T. Interparticle dipolar interactions were also considered. In the non-interacting system and for low temperature, hysteresis is observed in the z magnetization component M z for both orientations of the anisotropy axis and only in the y component (M y) for the random case. Furthermore, the loop areas were estimated, and increased with ω for all orientations and ( M y , M z ) components. At higher temperatures the superparamagnetic state is observed, so both the blocking temperatures T B and loop areas were estimated. The values of T B were close from the room temperature T R = 300 K for all components, and the areas decreased with T but they are practically not zero at T B. When dipolar interactions are included a new scenario is revealed. In the low temperature regime, the blocked state is present for both M y and M z for all anisotropy orientations, and extends beyond the interval of amplitudes H 0 estimated theoretically for the model without interactions and fixed anisotropy. The loops are displaced with respect to the origin of the magnetization-external field plane. When the temperature is raised, the blocked state extends for a larger range than the model without interactions, and the loop displacement decreases with T. These behaviors could be explained by observing that the average dipolar field per particle produces an effective field – the sum of both dipolar and external field – that is asymmetric with respect to the zero field line at low temperatures, becomes half-wave symmetric at higher temperatures, so the the centered character of the loops is restored. In addition, the loop areas show a peak for all orientations of the anisotropy axes in an intermediate range of temperatures. This result can be associated with a dominance of the anisotropy induced by the dipolar field. Finally, by comparing the areas of the loops of the models with and without interactions, it was found that the non-interacting model have larger areas at low temperatures that vanish near the room temperature, unlike the areas of the model with interactions due to the extension of the blocked state. [ABSTRACT FROM AUTHOR]

• Transport properties of Mn 2 CoSn were studied. • Mn 2 CoSn has large electrical resistivity. • Abnormal Hall coefficient electrical resistivity as ∼ρ2. Transport properties of bulk samples and melt-spun ribbons of Mn 2 CoSn alloy were investigated. It was found that Mn 2 CoSn is a high-resistance compound with the value of electrical resistivity ρ ∼ 300 μOhm·cm at room temperature and demonstrates semiconducting behavior of ρ as a function of temperature. A change in the dominating conductivity type from hole-like to electron-like takes place upon heating above ≈137 K. Abnormal Hall coefficient R S is large and depends on electrical resistivity as R S ∼ ρ2. [ABSTRACT FROM AUTHOR]

• The C-doped SnO 2 induced a new state resulting the half-metallic characteristic. • The Sn 0.98 Mn 0.02 O 2 shows the antiferromagnetic (AFM) stability belongs to super-exchange coupling type. • For Sn 0.98 Mn 0.02 (O 1-x C x) 2 system, we predicted two statements, the presence of the FM and the ferrimagnetic stabilities. In this paper, the challenge is to investigate the possibility to have the ferromagnetic or/and ferrimagnetic behavior connected to Sn 0.98 Mn 0.02 (O 1-x C x) 2 system at low concentration (x = 0.02, 0.03, 0.04 and 0.05) at room temperature (RT). We utilized the Korringa-Kohn-Rostoker method combined with the Coherent Potential Approximation (KKR-CPA). The C-doped SnO 2 induced the half-metallic characteristic located on the Fermi level and the presence of the double-exchange coupling type belongs to the ferromagnetic (FM). The Sn 0.98 Mn 0.02 O 2 shows the antiferromagnetic (AFM) stability belongs to super-exchange coupling type. For Sn 0.98 Mn 0.02 (O 1-x C x) 2 system, we predicted two statements, the presence of the FM stability where (x = 0.03) and the ferrimagnetic stability where (x = 0.02, 0.04, 0.05). The Curie temperature (T C) can be estimated within the mean field approximation (MFA), our calculations predicted 358.45 K for Sn(O 0.95 C 0.05) 2 and 402.26 K for Sn 0.98 Mn 0.02 (O 0.95 C 0.05) 2. The ferrimagnetic materials are useful for many applications. [ABSTRACT FROM AUTHOR]

• The mechanical and magnetic properties of AlM2B2 have been investigated. • The low hardness indicates a delamination deformation. • In AlM 2 B 2 the magnetism ferro- to antiferromagnetic with increasing Mn content. • AlFeMnB 2 shows a ferrimagnetic exchange interactions. • DFT calculations indicate weakening of the magnetic interactions upon substitution. The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe 2 B 2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b -axis, similar to AlFe 2 B 2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe 2 B 2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB 2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe 2 B 2. The Mn-Mn exchange interactions in AlMn 2 B 2 are found to be very small. [ABSTRACT FROM AUTHOR]

Highlights • Magnetoimpedance in systems with magnetic insulators. • Ferrimagnetic insulator yttrium iron garnet capped by copper. • Magnetoinductive effect in the whole frequency range. • Ferromagnetic resonance effect even at low frequencies. Abstract We investigate the magnetization dynamics through magnetoimpedance effect in films of ferrimagnetic insulator yttrium iron garnet capped by copper. Thereby, we explore the magnetoimpedance in systems with magnetic insulators by varying the thickness of the magnetic material, and probe current frequency. We observe that the difference of electrical nature of the layers composing the films gives rise to the magnetoinductive effect in the whole frequency range, as well as favors the appearance of the ferromagnetic resonance effect even at low frequencies. We discuss the experimental results in terms of the structural features of the magnetic material, its magnetic properties, and the different mechanisms governing the magnetization dynamics. The results place the films of ferrimagnetic insulator yttrium iron garnet capped by copper exhibiting magnetoimpedance effect as very attractive candidates for application as probe element in magnetic sensors operating at low frequencies and with energy-efficient technologies. Further, we disclose an auspicious technique to look at the magnetization dynamics in magnetic materials and we provide a new perspective to solve questions related to the integration of insulator ferrimagnetic materials with the coplanar waveguide in broadband frequency applications. [ABSTRACT FROM AUTHOR]

Highlights • We synthesized osingle phase SrCo 1−x V x O 3−d compounds by solid state reaction method. • The samples showed ferrimagnetic type of transitions above room temperature. • The negative magnetoresistance value up to 18% was observed at low temperature. • Large exchange bias effect H EB ∼ 1 kOe at room temperature and H EB ∼ 8.22 kOe at 10 K. • Giant exchange bias is due to compensated host and weakly ordered magnetic regions. Abstract Materials with room temperature exchange bias (EB) effect are important for future applications in electronics/spintronics industry. Nevertheless, such materials are rare in bulk and show very low exchange bias field (∼100 Oe) at room temperature. In this work, we have shown the appearance of large exchange bias effect in "314-type" SrCo 1−x V x O 3−δ (x = 0.05 and 0.1) materials. X-ray diffraction patterns confirm that all the samples crystallize in a "314-type" tetragonal structure (space group: I4/mmm) with 2a p × 2a p × 4a p type unit cell. Both the samples exhibit ferrimagnetic-type transitions above room temperature. Detailed magnetic measurements highlight a large exchange bias effect with H EB ∼ 1 kOe at room temperature and H EB ∼ 8.22 kOe at 10 K. The introduction of V5+ in the structure actually breaks the compensated antiferromagnetic (AFM) structure. The existence of nearly compensated host and weakly ordered magnetic regions imparts the exchange bias effect in these samples. [ABSTRACT FROM AUTHOR]

Highlights • Anomalous magnetic response of Y 3-x Fe 5+x O 12 garnet films was observed. • An additional orientational phase transition was revealed. • Spontaneous magnetization flip in a wide temperature range was detected. • Spontaneous magnetization oscillates in the paramagnetic state of the sample. • Magnetic response of the films exhibits a field and temperature reverse hysteresis. Abstract Anomalous properties both of the dynamic magnetic susceptibility and the spontaneous magnetization of Y 3 - x Fe 5 + x O 12 garnet films have been experimentally observed. The most significant anomalies are the following: (a) an orientational magnetic transition at room temperature in the range of the applied magnetic field of 300–700 Oe; (b) a spontaneous magnetization vector reversal in the temperature range of 110–275 °C and the corresponding jump of the dynamic susceptibility at zero magnetic field; (c) oscillations of the magnetization in the paramagnetic state of the sample and the corresponding jumps of the dynamic susceptibility at the planar magnetic field H = 200 Oe. It has been established that all reported anomalies exhibit an inverse behavior, namely, with decrease of the applied magnetic field (or temperature) a reverse hysteresis of the field (or temperature) dependences both of the dynamic magnetic susceptibility and the spontaneous magnetization is observed. Possible reasons for such a behavior of the measured dependences are also discussed. [ABSTRACT FROM AUTHOR]

Highlights • Magnetic and structural properties of Ni(Mn) 1.75 Co 0.25 Mn(Ni) 1+x Sn 1-x are studied. • For both alloys, austenite-martensite transition realizes at high Mn (Ni) content. • Ferrimagnetic order is favorable for Mn-Co-Ni-Sn in austenite and martensite. • Magnetization changes greatly at structural transition for Ni-Co-Mn-Sn (x = 0.75). Abstract The influence of partial Mn and Co content on magnetic properties and martensitic transformation in full Heusler compounds Ni-Co-Mn-Sn with the regular and inverse structure is studied theoretically by first-principles calculations within density functional theory. The optimized lattice parameters, magnetic moments and bulk moduli are calculated. It is shown that the substitution of Sn for Mn atom in the regular structure and of Sn for Ni atom in the inverse structure leads to an appearance of stable martensitic phase. For both considered systems with excess Ni and Mn content, the magnetic reference state of austenite and martensite is found to be the ferrimagnetic one except for Ni 1.75 Co 0.25 Mn 1.75 Sn 0.25 . For the latter, martensitic and austenitic phases are ordered ferri- and ferromagnetically that results in a large change in magnetization. [ABSTRACT FROM AUTHOR]

Highlights • Dependence of μ ij , q ij , and α ij in BiFeO 3 on arbitrary orientations is investigated. • Anisotropy characteristics of μ ij , q ij , and α ij in BiFeO 3 are presented. • The optimal orientations for achieving the largest μ ij ′ , q ij ′ , and α ij ′ are specified. Abstract Through coordinate transformation approach, crystal orientation dependences of magnetic properties have been investigated in the three dimensional space for bismuth ferrite (BiFeO 3). Permeabilities μ 11 ′ , μ 33 ′ , piezomagnetic constants q 31 ′ , q 33 ′ , and magnetoelectric coefficients α 12 ′ , α 31 ′ along arbitrary orientations were presented based on magnetic and crystalline asymmetry characteristics of trigonal BiFeO 3 below the Neel temperature. μ 11 ′ is a constant while the max μ 33 ′ = μ 11 ′ = 2.68 lies in [ n k 0] axes. q 31 ′ and q 33 ′ show very similar orientation dependences with their absolute maximas (10−13 m/A) both lying in directions at ϕ = 30°, 90°, and 150° inside XOY plane. α 12 ′ and α 31 ′ show the contrary orientation dependences with their maximas (120 mV/cm Oe) existing along [0 0 1] and [ n k 0] axes, respectively. The results suggest that by adopting optimal directions, the magnetic parameters of BiFeO 3 could be optimally used. [ABSTRACT FROM AUTHOR]

Highlights • Magnetization, Cotton Mouton, and specific heat results obtained on DyIG single crystals are reported. • The first-order nature of the spin reorientation phase transition at T SR = 15 K is confirmed. • This ferrimagnet exhibits low temperature anomaly near the Belov point T B = 42 K. • The data are analyzed taking into consideration previous reports about magnetodielectric effect at T SR and Schottky anomaly around T B. Abstract Measurements of magnetization and Cotton Mouton effect (CM) under external magnetic field (H ex) combined with specific heat experiments at H ex = 0, were performed on dysprosium iron garnet Dy 3 Fe 5 O 12 (or DyIG) single crystals. The low-temperature dependences of some magnetic, magneto-optical and thermodynamic quantities, such as spontaneous magnetization, both magnetic and CM susceptibilities and the excess specific heat due to the contribution of the Dy3+ ions only, give rise to the appearance of two types of anomalies. The first one which is related to the 'low temperature paraprocess' effect, occurs in the region of the 'Belov point' T B predicted at 42 K. Whereas the second one, which is due to the previous first-order spin reorientation phase transition, takes place at T SR = 15 K. The easy axis of magnetization defined by the resultant iron sublattice magnetization vector M Fe , which remains along the 〈1 1 1〉 direction above T SR , changes spontaneously below T SR and becomes aligned along the low symmetry angular 〈u u w〉 phase. The results are analyzed taking into account those reported earlier, such as the negative magnetodielectric property for H ex < 10 kOe and the Schottky effect which are related to the anomalies observed respectively in the temperature dependences of the dielectric constant at T SR and the excess specific heat near T B. [ABSTRACT FROM AUTHOR]

Highlights • The exchange spring magnet formed by a soft magnetic oxide and hard magnetic nitride. • Their exchange-spring behavior was evidenced by recoil permeability measurements. • The fully dense ferrite/Sm 2 Fe 17 N 3 magnet exhibited resistivity of about 4000 μΩ cm. Abstract Typical exchange spring magnets are composed of two phases, a rare-earth hard magnetic material and a metallic soft magnetic material, whose magnetization value is higher than those of hard magnetic phases, such as α-Fe, Fe-B, or Fe-Co. A novel high-electrical-resistance composite magnet was fabricated by consolidating micron-sized ferromagnetic nitride Sm 2 Fe 17 N 3 powder particles coated with a continuous nano-sized soft magnetic ferrite oxide layer, which suppressed intergrain conductivity but sustained the magnetic exchange interactions between grains [21]. A non-magnetic resin or ceramic insulator may suffice for the coated layer but gives rise to high electrical resistance of the magnet with large deterioration of magnetization. The soft magnetic ferrite oxide layer not only suppressed intergrain conductivity, but also only slightly reduced the magnetization of the magnet. At present, the only exchange spring magnet having a combination of a soft magnetic oxide and hard magnetic nitride is the ferrite/Sm 2 Fe 17 N 3 composite magnet. Sm 2 Fe 17 N 3 powder particles with a size of 2 μm were coated with an "iron ferrite" layer with a grain size of about 10 nm by ferrite plating, which is an aqueous process, following which the samples were consolidated by the explosive consolidation (EC) technique. The coercivity and rectangularity of the ferrite/Sm 2 Fe 17 N 3 composite magnet decreased slightly compared to those of a Sm 2 Fe 17 N 3 magnet. The fully dense ferrite/Sm 2 Fe 17 N 3 magnet exhibited a resistivity of about 4000 μΩ cm, which is ten times larger than that of a fully dense Sm 2 Fe 17 N 3 magnet. Thus, the soft magnetic ferrite layer in the composite magnet maintained the magnetic exchange coupling between ferromagnetic Sm 2 Fe 17 N 3 grains and simultaneously suppressed intergrain electrical coupling to increase the resistivity. This decreased the eddy current loss and improved the high-frequency characteristics of the composite magnets. Therefore, ferrite/Sm 2 Fe 17 N 3 composites are promising materials for magnets that are operated at high frequencies in advanced applications, such as electric vehicle magnets. [ABSTRACT FROM AUTHOR]

Highlights • Effect of volume change on anisotropy. • Spin reorientation transition. • High volume stability of the magnetic properties. • Moderate decrease of the Curie temperature with increasing pressure. Abstract The magnetic properties of HoCo 12 B 6 ferrimagnetic compound are investigated versus the magnetic field, temperature and pressure. The magnetic phase diagram exhibits three remarkable temperatures: the ordering temperature T C , the spin reorientation temperature T SR and the compensation temperature T COMP at 147 K, 76 K and 47 K respectively. In HoCo 12 B 6 intermetallic system the spontaneous magnetization resulting from the antiparallel coupling of the magnetic moments of Ho and Co sublattices is pressure insensitive at lowest temperatures whereas it decreases with pressure at temperature range above T SR. The mean Co magnetic moment is small (<0.5 µ B) in the studied compound and exhibits a weak pressure dependence. In addition, significant pressure effects have been observed on both the spin reorientation transition and the Curie temperatures. A value of dT C /dp = −3.5 ± 0.4 K GPa−1 is dominated by the Co sublattice contribution. The spin reorientation transition temperature is also found to decrease versus pressure dT SR /dp = −4.2 ± 0.4 K GPa−1. The compensation temperature where the Ho and Co sublattices have the same magnitude but opposite direction does not vary significantly with applied pressure in the investigated pressure range (up to 1 GPa). The results of pressure dependence of the magnetic properties are compared to earlier results on other R-Co-B borides. HoCo 12 B 6 compound confirmed the remarkably high volume stability of the magnetic properties of the RCo 12 B 6 compounds with the itinerant character of magnetism and low values of both the T C and magnetization. [ABSTRACT FROM AUTHOR]

Highlights • Magnetic H - T phase diagram of a Fe/Gd ferrimagnetic superlattice is obtained. • Collinear, twisted and surface twist magnetic states are identified. • Two spectral branches of ferromagnetic resonance are observed. • The observed modes correspond to different types of non-uniform precession in Gd. Abstract Static and dynamic magnetic properties of a ferrimagnetic Fe (35 Å) / Gd (50 Å) 12 superlattice were investigated in a wide 4–300 K temperature range using magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) techniques. The multilayer structure was sputtered on a transparent glass substrate which made it possible to perform MOKE measurements on both Fe and Gd terminated sides of the superlattice. These experiments allowed us to detect a transition between field-aligned and canted magnetic states on both sides of the film and to distinguish between the bulk and surface twisted phases of the superlattice. As a result, the experimental H - T magnetic phase diagram of the system was obtained. FMR studies at frequencies 7–36 GHz demonstrated a complex evolution of absorption spectra as temperature decreased from room down to 4 K. Two spectral branches were detected in the sample. Theoretical simulations show that the observed spectral branches correspond to different types of inhomogeneous resonance modes in the multilayer with non-uniform magnetization precession inside Gd layers. [ABSTRACT FROM AUTHOR]

The effect of transition to disordered phase on AC conductivity in the two-dimensional frustrated ferrimagnetic model in the square lattice at T = 0 is investigated. The spin conductivity, σ reg ( ω ) is determined for different values of frustration parameters J 2 S and J 2 s that separates the different phases such as the ferrimagnetic phase and the collinear phase. We obtain a small influence of this phase transition on spin conductivity. Furthermore, we present the behavior of the half-width of S ( q → , ω ) that gives the information about the scattering of magnons at long wavelength range. [ABSTRACT FROM AUTHOR]

In this work, we study the magnetic properties in a diluted ferrimagnetic materials structure, composed with three areas, by Monte Carlo simulations. The system consists of two non-equivalent types of atoms A and B, two arrangements ABA and BAB are considered. The dilution effect concerns only the B atoms. The ground state phase diagrams are reported. The effect of exchange coupling interactions on the compensation temperature is investigated. The obtained results show that the system presents a compensation temperature and different behaviors when varying the coupling parameters and the dilution probability. [ABSTRACT FROM AUTHOR]

Atomically-flat thin films of ferrimagnetic insulator Tb 3 Fe 5 O 12 (TbIG) were grown on (1 1 1)-oriented Gd 3 Ga 5 O 12 (GGG) substrates by pulsed laser deposition. Magnetic measurements indicated the easy magnetic axis of TbIG film was out-of-plane, as a result of the substrate-induced compressive in-plane strain within the film. The temperature dependence of anomalous Hall effect (AHE) in Pt/TbIG bilayer was systematically studied with the applied magnetic field normal to the film plane, with square hysteresis AHE loops being observed. Reversal of AHE sign occurred twice between 10 K and room temperature, one at 50 K and another around 220 K, the latter of which was accompanied by complex magnetization switching behavior. The peculiar behavior of AHE loop around 220 K is closely related to the compensation point of TbIG. On the other hand, the sign change at 50 K was attributed to the modification of Pt electronic structure by TbIG. Our results highlight the relation between the AHE of Pt and magnetic properties of TbIG, which can be used for probing the magnetism in TbIG. [ABSTRACT FROM AUTHOR]

In this paper we propose an extension to the Handrich model considering the fluctuations in exchange energies between ions located in different magnetic sublattices. Thus, each magnetic sublattice has an amorphization parameter that changes with temperature. A systematic study of the magnetization as a function of temperature is performed, which allows to observe significant differences when such fluctuations are not considered. [ABSTRACT FROM AUTHOR]

Ca 2 CrOsO 6 was synthesized recently and measured to be an insulating ferrimagnet with a high magnetic ordering temperature of 490 K. To design a half metal, we substituted Cr with Mo and performed an investigation on Ca 2 AOsO 6 (A = Cr, Mo) by using the density functional theory. However, Ca 2 MoOsO 6 is an insulator with a small band gap in one spin direction. By applying external pressure, the small gap can be closed, making Ca 2 MoOsO 6 a compensated half metal. The estimated T c for Ca 2 MoOsO 6 under pressure is higher than the room temperature. Therefore, we expect that Ca 2 MoOsO 6 would be promising compound for spintronic devices. [ABSTRACT FROM AUTHOR]

Highlights • A new method is developed quantitative phase control in soft ferrimagnetic materials. • The method is based on thermomagnetometric analysis of the samples in magnetic field. • This method compared to X-ray diffraction analysis is more precise. • The method was successfully tested on the LiTi and LiZn ferrites. Abstract In this work, the method of quantitative ferrite phase control, which is based on thermomagnetometric analysis of the ferrite samples in magnetic field, was developed. The magneto-phase transitions in LiZn and LiTi ferrites with chemical formulas Li 0.5(1 x) Fe 2.50.5 x Zn x O 4 and Li 0.5(1+ x) Fe 2.51.5 x Ti x O 4 were studied, and their phase compositions were analyzed by both the developed method and X-ray diffraction analysis. It was shown that the thermomagnetometry method compared to X-ray diffraction analysis allows to examine more precisely the magnetic phases in synthesized ferrites with inhomogeneous phase composition. However, a complex analysis, using both X-ray and thermomagnetometry methods, will be the most optimal in case of the formation of non-magnetic and poor magnetic phases. [ABSTRACT FROM AUTHOR]

Highlights • The magnetic and thermodynamic properties of a ferrimagnetic bilayer superlattice are studied by Monte Carlo simulation. • The phase diagrams in different parameter planes were obtained. • Various types of magnetization curves are observed, depending on physical parameters and temperature. • The triple and double hysteresis loop behaviors exist for certain values of physical parameters. Abstract Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a ferrimagnetic mixed spin-1 and spin-3/2 Ising bilayer superlattice system on the honeycomb structure. The ground state phase diagrams of the system have been obtained for different single-ion anisotropies and exchange couplings. The system exhibits characteristic critical behaviors such as compensation points, the first- and second-order phase transition points as well as the tricritical points. The effects of the single-ion anisotropies and the exchange couplings on the magnetization, the susceptibility, the internal energy, the specific heat and the hysteresis loops are discussed in detail. Lots of interesting magnetic phenomena have been found, originating from the competitions among the anisotropies, the exchange couplings, the temperature and the external magnetic field. In particular, multiple cycle hysteresis loops behaviors such as the double and triple hysteresis loops have been discovered. Our results are in excellent agreement with previous theoretical studies. [ABSTRACT FROM AUTHOR]

Understanding spin dynamics in perpendicular exchange coupled ferrimagnetic materials is an issue of crucial importance for progress in information processing and recording technology. In this paper, the Landau-Lifshitz-Gilbert equation at atomistic-level is employed to model the perpendicular interfacial exchange effect in ferrimagnetic FeGd/FeTb soft/hard bilayer structures. Three types of magnetization switching features are identified by tuning the interfacial exchange strength to be weak coupling, partial coupling, and strong coupling. These features have been further verified by the dynamical simulations, showing the switched soft layer could also help the hard layer magnetization switching. Based on the coercivity difference of the soft layer and hard layer, the left- or right-shift perpendicular exchange bias effect has been theoretically modelled. [ABSTRACT FROM AUTHOR]

The effects of additives Bi 2 O 3 and MnCO 3 on the structural and magnetic properties of M-type Sr-hexaferrites (SrFe 12 O 19 ) prepared by a conventional solid-state reaction method were studied. The saturation magnetization value of undoped SrFe 12 O 19 is 71.8 emu/g; it increases to 72.6 emu/g and 74.2 emu/g with Bi 2 O 3 doping of 0.5 wt%and 1.0 wt%, respectively. However, abnormal grain growth occurs and the coercivity (H C ) decreases significantly in the 1 wt% Bi 2 O 3 -doped sample. Co-doping of 0.5 wt% Bi 2 O 3  + 0.5 wt% MnCO 3 is effective, because a higher saturation magnetization (73.1 emu/g) than that of undoped SrFe 12 O 19 could be achieved with a relatively large coercivity of ∼3.3 kOe. Based on the lattice parameter calculation, Bi 3+ preferably substitutes into Fe 3+ sites rather than Sr 2+ sites in M-type Sr-hexaferrite. The enhanced saturation magnetization can be attributed to the selective substitution of nonmagnetic Bi 3+ into the down-spin Fe 3+ site (4 f 1 or 4 f 2 ). [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMCs) comprised of ferrimagnetic and electrically insulating coating materials for iron powder are capable of increasing frequency ranges and efficiency of electromagnetic devices, nominally electric motors. Soft ferrites can withstand stress relieving temperatures and allow for reduction in eddy current contributions while minimally effecting magnetic performance. This work demonstrates the effectiveness of a NiZnCu-ferrite coating material of 5 wt%, 10 wt%, and 15 wt% on iron powder using traditional press and cure (700 °C) powder metallurgy techniques. Powder properties such as apparent density and Hall flow rate are used to determine effect of acoustic mixing procedure on coating uniformity. An increase in resistance and porosity are found for increasing coating amount, with subsequent decreases in density, permeability, and magnetic saturation. We find lower core loss values for increasing coating amount, related to eddy current loss, however, lower induction levels are also seen. Our work highlights the importance of soft ferrites, more specifically Ni 0.5 Zn 0.3 Cu 0.2 Fe 2 O 4 , and their ability to vastly improve SMC developments using more traditional powder metallurgy (PM) techniques. [ABSTRACT FROM AUTHOR]

Using the mean field approximation (MFA), we have successfully investigated the magnetic properties of the mixed spin S j = ± 3 , ± 2 , ± 1 , 0 and σ i = ± 3 2 , ± 1 2 Ising ferrimagnetic system in a graphene layer. The effects of different physical parameters, namely exchange interactions, anisotropies, external field and temperature on the critical, first-order, compensation and hysteresis behaviors have been examined. The results show that, for specific values of these parameters, interesting phenomena appeared, such as compensation and multi-loop hysteresis behavior. It was shown that the compensation phenomenon only occurs if the exchange interaction J A (interaction between spins σ i), is greater than a certain minimum value J A m i n. We have also shown that, for fixed values of the anisotropies, the relation between J A m i n and the exchange interaction J B (interaction between S j), is a linear one. In addition, we found that each of the behaviors mentioned above is sensitive to the change of a certain physical parameter. Finally, we have verified that our results are comparable with those of other works. • The effects of physical parameters on magnetic properties were examined. • The system presents a first- and second-order transition. • Compensation appears in the system for specific values of physical parameters. • The phenomenon of multi-loop hysteresis cycles is present in the system. [ABSTRACT FROM AUTHOR]

• Investigate the temperature-dependent AHE in sandwich structures composed of two RE-TM FIM layers. • Complex AHE phenomena explained by the magnetization reversal of individual layers, Hall sign reversal, and the SF transition in the GdFeCo layer. • A model is developed to provide a simplified explanation of the origin of these complex AHE loops. • The model unravels the complexity in AHE loops near and far from the T comp. • The model fits well with the experimental results. The anomalous Hall effect (AHE) has been a remarkable tool for characterizing the magnetic properties of thin films with perpendicular magnetic anisotropy. In this study, we investigate the temperature-dependent AHE in sandwich structures composed of two ferrimagnetic (FIM) layers with different coercivities, using rare-earth-transition-metal (RE-TM) materials. Complex triple AHE loops are obtained near the compensation temperature of GdFeCo, and these loops are explained by considering the magnetization reversal of the individual layers, Hall sign reversal, and the spin-flop transition in the GdFeCo layer. A model is developed to provide a simplified explanation of the origin of these complex AHE loops. This study elucidates the mechanism behind the unusual temperature-dependent AHE response of the technologically important RE-TM FIM films for spintronics applications. [ABSTRACT FROM AUTHOR]

The magnetic properties of the near-stoichiometric Tm 2 Fe 16 and Tm 2 Fe 19 compounds under hydrostatic pressures up to 1 GPa were studied. We have revealed that the high-temperature ferrimagnetic state easily magnetized in the basal plane is very sensitive to the volume changes and even moderate pressure is sufficient to its complete suppression and transformation to a helimagnetic state. At the same time, the low-temperature ferrimagnetic state easily magnetized along the hexagonal axis does not disappear under pressure and the temperature of its transition to the high-temperature magnetic states increases under pressure. The remarkable stability of the ground ferrimagnetic state under external pressure can be attributed to the strengthening of the uniaxial magnetic anisotropy and to the mutual perpendicular orientation of the magnetic moments in the ground and the high-temperature magnetic states. [ABSTRACT FROM AUTHOR]

A classical-quantum chain composed of regularly alternating Ising and Heisenberg spins is rigorously solved by considering two distinct local anisotropy axes of the Ising spins. The ground-state phase diagram and magnetization curves are examined depending on a spatial orientation of the applied magnetic field. The phase diagram totally consists of four distinct phases and a few macroscopically degenerate points, where an outstanding coexistence of perfect order and complete disorder occurs within the so-called ‘half-fire, half-ice’ state. The zero-temperature magnetization curves generally exhibit a smooth dependence on a magnetic field owing to a canting angle between two coplanar anisotropy axes of the Ising spins, which enforces a misalignment of the magnetization vector from a direction of the applied magnetic field. It is evidenced that the investigated spin-chain model reproduces magnetic features of the heterobimetallic coordination compound Dy(NO) 3 (DMSO) 2 Cu(opba)(DMSO) 2 (DMSO = dimethylsulfoxide, opba = orthophenylenebisoxamato). The high-field magnetization data reported for the powder sample of this polymeric coordination compound generally display a substantial smoothing on account of a powder averaging. [ABSTRACT FROM AUTHOR]

This article describes the synthesis of two superparamagnetic iron oxide nanoparticles (SPIONs) covered with different ligands – hydrophobic (oleic acid (OA)) and hydrophilic (tetraethyl ammonium (TEA)) – and the investigation of the effects of thermal treatments on the crystal structure of TEA-SPIONs or OA-SPIONs using X-ray powder diffraction data and parametric Rietveld refinements; we stablished non-crystallographic models to describe how the oxidation processes take place with increasing temperatures for the different systems. The morphological and magnetic properties revealed the nanoparticles have a mean diameter of ∼10 nm in the solid state and are superparamagnetic at room temperature. Magnetization measurements confirmed the superparamagnetic state for both systems and revealed smaller particle sizes and narrower size distribution for OA-SPIONs than for TEA-SPIONs. The thermomagnetic analyses show only the ferrimagnetic phase transition of magnetite for OA-SPIONs while in the TEA-SPIONs, besides the ferrimagnetic phase transition there is the appearance of an antiferromagnetic one disclosing the evolution of hematite phase probably on the surface of magnetite due to thermal cycles. [ABSTRACT FROM AUTHOR]

Magnetic dead layers (MDLs) are always undesirable in practical applications due to their highly frustrated spin configurations and severe degradation of host magnetism. Here we provide new insights in MDLs and unravel their attractive prospect for ferrimagnetic hybrid of Fe 3 O 4 and γ-Fe 2 O 3 (denoted as Fe 3 O 4 @γ-Fe 2 O 3 in the main text) to exhibit macroscopic quantum tunneling (MQT) phenomena in measureable kelvin range. The 3 nm-sized negatively-charged Fe 3 O 4 @γ-Fe 2 O 3 nanoparticles were immersed in various metal chloride solutions containing Mn 2+ , Co 2+ , Ni 2+ , Fe 3+ , and Fe 2+ cations to form cationic MDLs via electrostatic attraction. These man-made MDLs, if being of positive enough zeta potentials, greatly disordered the magnetic dipole interactions among Fe 3 O 4 @γ-Fe 2 O 3 nanoparticles and induce extra energy barrier to yield pronounced MQT effect in Fe 3 O 4 @γ-Fe 2 O 3 nanoparticles even though they were dispersed neither in water nor in oil. Their crossover temperatures dividing MQT and purely thermal relaxation were found to be one order of magnitude higher than reported values in other MQT systems, and more strikingly, they could be tailored by altering the soak period in our facile and scalable route. [ABSTRACT FROM AUTHOR]

The compensation behaviors of Fe II Fe III bimetallic oxalates with defects were explored by constructing a diluted spin-2 and spin-5/2 ferrimagnetic Ising model. Within the effective-field theory based on Glauber-type stochastic dynamic, the effects of the concentration of Fe II and Fe III ions on the compensation temperatures have been studied and the two-compensation points were found in Fe II Fe III bimetallic oxalates. The results showed that the compensation behaviors of the compounds were strongly affected by the presence of defects. In addition, the dilution enhanced the magnetization jumps of the compounds which have been found in earlier experimental and theoretical studies. In particular, the dynamic phase transition is absent in the nonequilibrium system with impurities in contrast to the corresponding equilibrium system. [ABSTRACT FROM AUTHOR]

Magnetic resonance characteristics of mixed chalcospinel nanocrystals CuCr 2 S x Se 4−x (x = 0 and 2) and Co x Cu 1−x Cr 2 S 4 (x = 0.1 and 0.2) have been investigated. It has been established based on TEM, SEM and resonance data that all the samples contain both blocks with sizes from 1 to 50 m of compacted nanosized crystallites and individual nanoparticles with sizes from 10 to 30 nm. The studies provide evidence of strong interparticle interaction in all the samples leading to high values of the blocking temperature. Magnetic dipolar field arise in the boundary regions of interacting adjacent nanocrystals below the blocking temperature. This results in inhomogeneous broadening of the magnetic resonance spectrum along with appearance of additional absorption lines. With increase in magnetic anisotropy at low temperatures, a shift of the resonance field along with line broadening are observed for all the studied compounds due to freezing of the moments in the nanoparticles, both in the individual and compacted ones. A gapped characteristic of the resonance spectrum is established below the freezing temperature T fr , with the energy gap defined by the averaged magnetic anisotropy < H A >. Anionic substitution of sulfur by selenium results in a decrease in the magnetic anisotropy. In contrast, cationic substitution of copper by cobalt increases the magnetic anisotropy due to a strong contribution from the latter ion. [ABSTRACT FROM AUTHOR]

Bilayers consisting of magnetically hard TbFeCo and soft GdFeCo alloy were fabricated. Exchange-spring and sharp switching in a step-by-step fashion were observed in the TbFeCo/GdFeCo hard/soft bilayers with increasing GdFeCo thickness. A perpendicular exchange bias field of several hundred Oersteds is observed from the shift of minor loops pinned by TbFeCo layer. The perpendicular exchange energy is derived to be in the range of 0.18–0.30 erg/cm 2 . The exchange energy is shown to increase with the thickness of GdFeCo layer in the bilayers, which can be attributed to the enhanced perpendicular anisotropy of GdFeCo layer in our experimental range. [ABSTRACT FROM AUTHOR]

We present a first-principles study of electronic structures and magnetic properties in Ni-doped BiFeO 3 using the density functional theory + U methods. The BiNi x Fe 1-x O 3 (x = 0.125, 0.25, 0.5) multiferroic ceramics represent ferromagnetic properties due to the ferrimagnetic order in Ni-O-Fe, and the magnetic moment rises with increase in Ni doping concentration agreeing well with experimental results. Ni atoms prefer to occupy the diagonal positions in the quasi-plane Ni-O-Fe eight-membered ring. Charge transfer from Bi 6 s state to Ni 3 d state through O 2 p orbital lead to the 2+ oxidation state of Ni, indicating high Néel temperatures of BiNi x Fe 1-x O 3 , and the electronic state of the system can be described as Bi 4+ x Bi 3+ 1-x Ni 2+ x Fe 3+ 1-x O 3 . The spin polarization of Bi 6 s state and O 2 p state near the Fermi level contributes to the total magnetic moment. A spin-polarized acceptor level of about 0.4 eV constituted by Bi 6 s state and O 2 p state is found, which is responsible for the increase in leakage current of Ni-doped BiFeO 3 . [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of doped ferrite Zn 0.3 Cu 0.7 Fe 1.5 Ga 0.5 O 4 have been studied by means of the neutron diffraction method at high pressures up to 4.7 GPa and in temperature range 300–425 K. By increasing the temperature and the pressure, a gradual suppression of the magnetic moments of iron ions in both A and B crystallographic sites was observed. This effect corresponds to a magnetic phase transition from the ferrimagnetic state to paramagnetic one. The lattice parameters, interatomic bond lengths and angles, magnetic moments of iron ions as functions of temperature and pressure were obtained. Upon compression, the magnetic ordering temperature of studied ferrite decreases with a large pressure coefficient dT c / dP  = −19(1) K × GPa −1 . [ABSTRACT FROM AUTHOR]

In this paper we report single step large scale synthesis of highly crystalline iron oxide nanoparticles viz. magnetite (Fe 3 O 4 ) and maghemite (γ-Fe 2 O 3 ) via gas phase condensation process, where micron sized iron metal powder was used as a precursor. Selective phases of iron oxide were obtained by variation of gas flow rate of oxygen and hence partial pressure of oxygen inside the plasma reactor. Most of the particles were found to possesses average crystallite size of about 20–30 nm. The DC magnetization curves recorded indicate almost super-paramagnetic nature of the iron oxide magnetic nanoparticles. Further, iron oxide nanoparticles were analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy and Mossbauer spectroscopy. In order to explore the feasibility of these nanoparticles for magnetic damper application, rheological studies have been carried out and compared with commercially available Carbonyl Iron (CI) particles. The nanoparticles obtained by thermal plasma route show improved dispersion which is useful for rheological applications. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation is used to study the magnetic properties of mixed spin (3/2, 1) disordered binary alloys on simple cubic, hexagonal and amorphous magnetic ultra-thin films with 18 × 18 × 2 atoms. To this end, at the first approximation, the exchange coupling interaction between the spins is considered as a constant value and at the second one, the Ruderman–Kittel–Kasuya–Yosida (RKKY) model is used. Effects of concentration, structure, exchange interaction, single ion-anisotropy and the film size on the magnetic properties of disordered ferromagnetic and ferrimagnetic binary alloys are investigated. Our results indicate that the spontaneous magnetization and critical temperatures of rare earth-3 d transition binary alloys are affected by these parameters. It is also found that in the ferrimagnetic state, the compensation temperature ( T com ) and the magnetic rearrangement temperature ( T R ) appear for some concentrations. [ABSTRACT FROM AUTHOR]

We have prepared a composite of ferrimagnetic ferrite Co 1.75 Fe 1.25 O 4 and non-magnetic oxide BaTiO 3 . The ferrite composition Co 1.75 Fe 1.25 O 4 has been prepared by chemical co-precipitation and subsequently heated at different temperatures. The heat treated ferrite powder has been mixed with BaTiO 3 powder with mass ratio 1:1 and the mixed powder has been finally heated at 1000 °C to form composite material. Structural phase of the composite material has been confirmed by high quality Synchrotron X-ray diffraction pattern and Micro-Raman spectra. The grain surface morphology and elemental composition have been studied by Scanning electron microscope and Energy dispersive X-ray analysis. The distribution of magnetic exchange interactions and blocking behavior of the ferrimagnetic grains in composite samples has been understood by analyzing the temperature and magnetic field dependence of dc magnetization. Finally, information on modified micro-structure and ferrimagnetic parameters in composite samples has been obtained as the variation of annealing temperature of the ferrite component before making composite. [ABSTRACT FROM AUTHOR]