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A systematical investigation was carried out on structure and magnetic properties in SmFe9−xVx (x = 0.4, 0.8, 1.2) compounds prepared by a single-roller quenching method. The high cool-down rate leads to metastable TbCu7 phase in the parent compound, which gradually transforms into equilibrium ThMn12 structure with V-doping content increasing. The Curie temperature increases from 470 to 590 K with V doping, which is consistent with the phase transformation. Surprisingly, simultaneous increase in both coercivity and remanence is resulted by V doping, reaching the highest value of 685 kA·m−1 and 44.8 × 10−3 A·m2·g−1 in x = 1.2 compound, respectively. This phenomenon can be explained by the combination of phase transformation and intergranular exchange coupling through δM-H plots. [ABSTRACT FROM AUTHOR]

The effect of the seed layers on the magnetic properties of the giant magnetoresistance thin films has received a lot of attention. Here, a synthetic spin valve film stack with a wedge-shaped NiFeCr seed layer is deposited and annealed following a zero-field cooling procedure. The film crystallinity and magnetic properties are studied as a function of the NiFeCr seed layer thickness. It is found that the exchange coupling field from the IrMn/CoFe interface and the antiferromagnetic coupling field in the synthetic antiferromagnet both increase as the seed layer thickness increases, indicating the perfection of film texture. In this film, the critical thickness of the NiFeCr seed layer for the formation of the ordered IrMn3 texture is about 9.3 nm. Meanwhile, a reversal of the pinning direction in the film is observed at this critical thickness of NiFeCr. This phenomenon can be explained in a free energy model by the competition effect between the exchange coupling and the interlayer coupling during the annealing process. [ABSTRACT FROM AUTHOR]

It would be helpful to achieve appropriate synthetic routes to attain larger-scale production at industrial levels of nanocomposites at low costs. In the present work, diphasic composites with core–shell nanostructures formed by La2Fe2O6/CoFe2O4 are investigated. The core–shell structure is fabricated via different preparation methods. The advantages and the demerits of the synthesis techniques are discussed. The presence of both the spinel CoFe2O4 nano ferrite and orthorhombic La2Fe2O6 perovskite phases is revealed by X-ray diffraction. XPS spectroscopy is utilized to investigate the chemical composition of the prepared samples. The hysteresis loops of the prepared samples exhibit a smooth loop that is resulted from the existence of two homogeneous magnetic phases. For the first time, it has been found that the preparation conditions have the advantage of reducing the switching field distribution value for the core–shell nanoparticles. Exchange coupled core–shell nanoparticles present a high potential to regulate the magnetic properties for numerous applications such as heavy metal removal and/or data storage devices. The maximum adsorption capacity (qm) of Cr III on the core–shell (S3) is higher compared to other adsorbents previously testified in the literature. The cost-effective and eco-friendly prepared core–shell samples with good metal removal capacity have great potential for commercialization. [ABSTRACT FROM AUTHOR]

Exchange-coupling between soft- and hard-magnetic phases plays an important role in the engineering of novel magnetic materials. To achieve exchange coupling, a two-phase microstructure is necessary. This interface effect is further enhanced if both phase dimensions are reduced to the nanometer scale. At the same time, it is challenging to obtain large sample dimensions. In this study, powder blends and ball-milled powder blends of Fe-SmCo5 are consolidated and are deformed by high-pressure torsion (HPT), as this technique allows us to produce bulk magnetic materials of reasonable sizes. Additionally, the effect of severe deformation by ball-milling and severe plastic deformation by HPT on exchange coupling in Fe-SmCo5 composites is investigated. Due to the applied shear deformation, it is possible to obtain a texture in both phases, resulting in an anisotropic magnetic behavior and an improved magnetic performance. [ABSTRACT FROM AUTHOR]

(1-x) SrFe 10 Al 2 O 19 / (x) Co 0.6 Zn 0.4 Fe 2 O 4 -(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by 'one-pot' self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of −42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe 10 Al 2 O 19 /(10 wt %)Co 0.6 Zn 0.4 Fe 2 O 4 at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe 10 Al 2 O 19 /Co 0.6 Zn 0.4 Fe 2 O 4 nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz). [ABSTRACT FROM AUTHOR]

Control of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast‐response information storage and processing devices. Previously, magnetic‐cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high‐quality single‐phase chromium oxynitride thin films using in‐situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (R3¯c) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads. [ABSTRACT FROM AUTHOR]

Classical, i.e., non-quantum, communications include configurations with multiple-input multiple-output (MIMO) channels. Some associated signal processing tasks consider these channels in a symmetric way, i.e., by assigning the same role to all channel inputs, and similarly to all channel outputs. These tasks especially include channel identification/estimation and channel equalization, tightly connected with source separation. Their most challenging version is the blind one, i.e., when the receivers have (almost) no prior knowledge about the emitted signals. Other signal processing tasks consider classical communication channels in an asymmetric way. This especially includes the situation when data are sent by Emitter 1 to Receiver 1 through a main channel, and an "intruder" (including Receiver 2) interferes with that channel so as to extract information, thus performing so-called eavesdropping, while Receiver 1 may aim at detecting that intrusion, which leads to a decision problem (existence of intrusion/no intrusion). Part of the above processing tasks have been extended to quantum channels, including those that have several quantum bits (qubits) at their input and output. For such quantum channels, beyond previously reported work for symmetric scenarios, we here address asymmetric (blind and non-blind) ones, with emphasis on intrusion detection and additional comments about eavesdropping. To develop fundamental concepts, we first consider channels with exchange coupling as a toy model. We especially use the general quantum information processing framework that we recently developed, to derive new attractive intrusion detection methods based on a single preparation of each state. Finally, we discuss how the proposed methods might be extended, beyond the specific class of channels analyzed here. [ABSTRACT FROM AUTHOR]

In the present work, the synthesis of Mn0.5Zn0.5CdxFe2-xO4 (0.0 ≤ x ≤ 0.5) nanoparticles (MnZnCd ferrite NPs) were achieved by sol-gel combustion approach. The results of the cadmium contribution on structural, morphological, and magnetic properties have been researched. X-ray diffraction (XRD) patterns of nanocomposites confirmed the co-existence of cubic spinel ferrite phases. TEM images of the nanoparticles confirmed the cubical structure with agglomeration to a certain extent. The average particle size of the products was calculated as around 14 nm. Magnetic peculiarities of the MnZnCd ferrite NPs were assessed by using a VSM instrument at RT and 10 K. Samples showed ferromagnetic behavior at both measurement temperatures. The various magnetic parameters for the produced nanocomposites were determined. It is found that the magnetization value (Ms) increases for lower Cd2+ doping content and decreases afterward. The changes in magnetic parameters were ascribed to numerous factors like the distribution of cations, the A-B super-exchange interactions, and the purity of samples. Highlights: Mn0.5Zn0.5CdxFe2-xO4 nanoparticles were prepared via sol–gel combustion approach. MnZnCd ferrite NPs showed ferromagnetic behavior. Magnetic interpretation of Cd2+ doping to Mn0.5Zn0.5Fe2O4 host material. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties of methane (CH4) heat-treated Sr-hexaferrite powders during the re-calcination process were investigated and compared with the magnetic properties of conventionally synthesized Sr-hexaferrite powder. Gradual changes in the magnetic behavior of the produced powder in each re-calcination stage were investigated using magnetization curves obtained from the vibration sample magnetometry (VSM) technique. First, the initial Sr-hexaferrite powder was prepared by the conventional route. Then the powder was heat treated in a dynamic CH4 atmosphere in previously optimized conditions (temperature: 950 °C, gas flow rate:15 cc min−1 and time: 30 min), and finally, re-calcined in various temperatures from 200 to 1200 °C. By investigating the hysteresis loops, we found the transition temperature of soft to hard magnetic behavior to be 700 °C. The maximum ratio Mr/Ms was obtained at temperatures of 800–1100 °C. At 1100 °C, and despite the Sr-hexaferrite single phase, the magnetic behavior showed a multiphase behavior that was demonstrated by a kink in the hysteresis loop. Uniform magnetic behavior was observed only at 900 °C and 1000 °C. Although the ratio Mr/Ms was almost the same at these temperatures, the values of Mr and Ms at 1000 °C were almost double of 900 °C. At 1000 °C, the second quadrant of hysteresis curve had the maximum area. Therefore, 1000 °C was the optimum temperature for re-calcination after CH4 gas heat treatment in the optimized conditions. Due to the presence of a small amount of hematite soft phase at 1000 °C, the most probable reason for the exclusive properties of the optimized product may be the exchange coupling phenomenon between the hard Sr-hexaferrite phase and the impurity of the soft hematite phase.

In this work, we have studied the effect of internal coupling in magnetic nanoparticles with inverted core-shell structure (antiferromagnet-ferrimagnet) and also magnetic surface anisotropy, performing Monte Carlo simulations based on a micromagnetic model applied in the limit of lattice size equal to the crystalline unit cell. In the treatment, different internal regions of the particle were labeled in order to analyze the magnetic order and the degree of coupling between them. The results obtained are in agreement with experimental observations in CoO/CoFe 2 O 4 and ZnO/CoFe 2 O systems, which we have taken as reference. It is observed that the surface anisotropy decreases the coercive field and the blocking temperature of the system. However, the core/shell coupling improves these properties and magnetically hardens the system. Our study shows that a significant magnetic stress is generated in the system, leading to magnetic disorder in the spins of the particle interface. On the other hand, in cases of high surface anisotropy, within a range of interfacial exchange values, a clear magnetic disorder is observed in the shell, which leads to anomalous behavior because the magnetization reversal process is no longer coherent., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Open-shell polycyclic aromatic hydrocarbons (PAHs) represent promising building blocks for carbon-based functional magnetic materials. Their magnetic properties stem from the presence of unpaired electrons localized in radical states of π character. Consequently, these materials are inclined to exhibit spin delocalization, form extended collective states, and respond to the flexibility of the molecular backbones. However, they are also highly reactive, requiring structural strategies to protect the radical states from reacting with the environment. Here, we demonstrate that the open-shell ground state of the diradical 2-OS survives on a Au(111) substrate as a global singlet formed by two unpaired electrons with antiparallel spins coupled through a conformational-dependent interaction. The 2-OS molecule is a "protected" derivative of the Chichibabin's diradical, featuring a nonplanar geometry that destabilizes the closed-shell quinoidal structure. Using scanning tunneling microscopy (STM), we localized the two interacting spins at the molecular edges, and detected an excited triplet state a few millielectronvolts above the singlet ground state. Mean-field Hubbard simulations reveal that the exchange coupling between the two spins strongly depends on the torsional angles between the different molecular moieties, suggesting the possibility of influencing the molecule's magnetic state through structural changes. This was demonstrated here using the STM tip to manipulate the molecular conformation, while simultaneously detecting changes in the spin excitation spectrum. Our work suggests the potential of these PAHs as all-carbon spin-crossover materials.

High-magnetization materials play crucial roles in various applications. However, the past few decades have witnessed a stagnation in the discovery of new materials with high magnetization. In this work, Ni/NiO nanocomposites are fabricated by depositing Ni and NiO thin layers alternately, followed by annealing at specific temperatures. Both the as-deposited samples and those annealed at 373 K exhibit low magnetization. However, the samples annealed at 473 K exhibit a significantly enhanced saturation magnetization exceeding 607 emu cm -3 at room temperature, surpassing that of pure Ni (480 emu cm -3 ). Material characterizations indicate that the composite comprises NiO nanoclusters of size 1-2 nm embedded in the Ni matrix. This nanoclustered NiO is primarily responsible for the high magnetization, as confirmed by density functional theory calculations. The calculations also indicate that the NiO clusters are ferromagnetically coupled with Ni, resulting in enhanced magnetization. This work demonstrates a new route toward developing artificial high-magnetization materials using the high magnetic moments of nanoclustered antiferromagnetic materials., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)

In this research, hard/soft CoFe2O4/Ni magnetic nanocomposite samples with different concentrations of Ni were successfully produced by a two-step mechanical alloying route. Single-phase CoFe2O4 (CFO), having the average particle size of 35 nm, saturation magnetization of 71 emu/g, and bandgap energy of 2.6 eV was synthesized via the mechanical alloying method. A mixture of as-synthesized CFO and 10, 30 and, 50 wt. % Ni powder has been severely milled to prepare magnetic nanocomposite samples. The effects of different Ni content on the characteristics of the nanocomposite samples have been investigated. FESEM images showed that the ductile nickel powder particles get flattened after 1 h milling, whereas the brittle CFO particles get fragmented by increasing milling time to 10 h. The single-phase-like hysteresis loop, and the switching field distribution curves alongside the simultaneous enhancements of maximum energy product and remanence reflect the presence of exchange spring phenomenon in the nanocomposite samples. Also, the diffuse reflectance spectroscopy (DRS) analysis evidence the reduction of bandgap energy for 10 wt.% Ni containing nanocomposite sample from 2.44 to 2.15 eV on increasing the milling time from 1 to 10 h. Under the optimum photocatalyst operating conditions, the CFO/10 wt% Ni sample exhibited the highest photocatalytic activity of 93.6% for methylene blue (MB) degradation in comparison with the cobalt ferrite sample. Eventually, the detailed kinetic and mechanism to describe the improvement of the photocatalytic performance were suggested. [ABSTRACT FROM AUTHOR]

Colloidal diluted magnetic semiconductor (DMS) nanocrystals are model systems for studying spin effects in semiconductor nanostructures with relevance to future spin-based information processing technologies. The introduction of excess delocalized charge carriers into such nanocrystals turns on strong dopant-carrier magnetic exchange interactions, with important consequences for the physical properties of these materials. Here, we use pulsed electron paramagnetic resonance (pEPR) spectroscopy to probe the effects of excess conduction band electrons on the spin dynamics of colloidal Mn(2+)-doped ZnO nanocrystals. Mn(2+) spin-lattice relaxation is strongly accelerated by the addition of even one conduction band electron per Zn1-xMnxO nanocrystal, attributable to the introduction of a new exchange-based Mn(2+) spin relaxation pathway. A kinetic model is used to describe the enhanced relaxation rates, yielding new insights into the spin dynamics and electronic structures of these materials with potential ramifications for future applications of DMS nanostructures in spin-based technologies.

Colloidal diluted magnetic semiconductor (DMS) nanocrystals are model systems for studying spin effects in semiconductor nanostructures with relevance to future spin-based information processing technologies. The introduction of excess delocalized charge carriers into such nanocrystals turns on strong dopant-carrier magnetic exchange interactions, with important consequences for the physical properties of these materials. Here, we use pulsed electron paramagnetic resonance (pEPR) spectroscopy to probe the effects of excess conduction band electrons on the spin dynamics of colloidal Mn(2+)-doped ZnO nanocrystals. Mn(2+) spin-lattice relaxation is strongly accelerated by the addition of even one conduction band electron per Zn1-xMnxO nanocrystal, attributable to the introduction of a new exchange-based Mn(2+) spin relaxation pathway. A kinetic model is used to describe the enhanced relaxation rates, yielding new insights into the spin dynamics and electronic structures of these materials with potential ramifications for future applications of DMS nanostructures in spin-based technologies.

Single-molecule magnets represent the ultimate size limit for spin-based information storage and processing; however, such applications require large spin relaxation barriers and blocking temperatures. Ongoing efforts to synthesize single-molecule magnets with higher barriers must take into consideration key physical parameters, such as spin ground state, S, and axial zero-field splitting parameter, D, which are both correlated to the barrier height. A third critical parameter that has received less attention is the exchange coupling constant, J. This constant determines the degree of separation between spin ground state and excited states, which must be sufficiently large in a single-molecule magnet to maintain slow magnetization dynamics at elevated temperatures, and also serves to shut down fast quantum relaxation pathways. Toward this end, one synthetic strategy to engender strong magnetic exchange is the incorporation of radical ligands into metal complexes. Within these complexes, the presence of direct exchange between paramagnetic ligand and metal units can result in exceptionally strong magnetic coupling, much stronger in fact than more common superexchange interactions. This review article provides a survey of radical ligand-containing single-molecule magnets, with a brief overview of other classes of metal-ligand radical complexes that could be exploited in the design of new single-molecule magnets. Furthermore, ligand-field and electronic structure considerations in dictating exchange strength and slow magnetic relaxation are highlighted, with the aim of helping to guide the synthesis of future radical ligand-containing single-molecule magnets with even stronger exchange coupling.

Laser-induced magnetization dynamics in a perpendicularly exchange-coupled TbFeCo/GdFeCo bilayer film are studied by using pump-probe magneto-optical Kerr spectroscopy. An ultrafast modulation effect on local magnetization orientation is observed. Such ultrafast magnetization reorientation in the GdFeCo layer is revealed to be triggered by the femtosecond laser pulse and driven by the effective exchange field. These processes occur within a timescale of hundreds of picoseconds, in which the field- and fluence-dependent dynamical behaviors are demonstrated. In addition, an atomistic Heisenberg model is proposed for studying the laser-induced magnetization dynamics by using micromagnetic simulation. The simulated results agree with the experimental phenomena and further reveal the underlying mechanism. These results show an approach for ultrafast manipulation of the local magnetization orientation in perpendicularly exchange-coupled structures.

The search for diluted magnetic semiconductors (DMSs) has gained immense research interest because of the coexistence of the charge and spin degree of freedom in a single substance to realize a particular class of spintronic devices, and a rare earth (RE)-doped transition-metal oxide (TMO) is one of the choices. This study intends to understand the effect of RE Sm3+ ion substitution in antiferromagnetic (AF) NiO nanoparticles (NPs) using modern cutting-edge techniques (synchrotron powder X-ray diffraction and soft X-ray absorption, Raman scattering, and superconducting quantum interference device magnetometry). A percolation threshold limit of about 1% incorporation of Sm3+ ions at the Ni2+ site was evident. An enhanced magnetic moment observed for an intermediate composition has been attributed to the interacting bound magnetic polaron. A core–shell model has been proposed such that the multivalent point defects reside at the surface of NPs, whereas the core of the particles retains AF properties. The exchange coupling mediated by interfacial frozen spins is the leading mechanism behind the magnetic memory effect at room temperature. The outcome of this study is vital for the future development of RE-functionalized TMO DMS spintronic devices and the understanding of their fundamental physics and chemistry. [ABSTRACT FROM AUTHOR]

Spin-state energetics of exchange-coupled copper complexes pose a persistent challenge for applied quantum chemistry. Here, we provide a comprehensive comparison of all available theoretical approaches to the problem of exchange coupling in two antiferromagnetically coupled bis-μ-hydroxo Cu(II) dimers. The evaluated methods include multireference methods based on the density matrix renormalization group (DMRG), multireference methods that incorporate dynamic electron correlation either perturbatively, such as the N-electron valence state perturbation theory, or variationally, such as the difference-dedicated configuration interaction. In addition, we contrast the multireference results with those obtained using broken-symmetry approaches that utilize either density functional theory or, as demonstrated here for the first time in such systems, a local implementation of coupled cluster theory. The results show that the spin-state energetics of these copper dimers are dominated by dynamic electron correlation and represent an impossible challenge for multireference methods that rely on brute-force expansion of the active space to recover correlation energy. Therefore, DMRG-based methods even at the limit of their applicability cannot describe quantitatively the antiferromagnetic exchange coupling in these dimers, in contrast to dinuclear complexes of earlier transition metal ions. The convergence of the broken-symmetry coupled cluster approach is studied and shown to be a limiting factor for the practical application of the method. The advantages and disadvantages of all approaches are discussed, and recommendations are made for future developments. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetism of Mn2SnS4 are analysed with full-potential first-principles calculations. In order to understand the possible influence of magnetic structure, we have performed calculations of total energies for both ferromagnetic (FM) and antiferromagnetic (AFM) orderings. Antiferromagnetic ordering is of three types. Our computed results reveal that Mn2SnS4 exhibits an AFM-I type antiferromagnetic ordering. The exchange interaction parameters, which reflects the electrostatic Coulomb repulsion of electrons on neighboring atoms and the Pauli principle, were estimated to be J1 = − 14.1 meV, J2= − 5.3 meV and J3 = − 8.2 meV according to the Heisenberg model. It was shown that all values are negative and J1 has the highest absolute value, demonstrating strong antiferromagnetic pairing dominating between the nearest magnetic Mn ions and weak antiferromagnetic coupling within the next-nearest Mn ions. The position of the sulfur atoms have no impact on the values of the aforementioned energies, which validates that the magnetism in Mn2SnS4 is dominated mainly by direct exchange. The associated energy differences involving spin orderings can be used to evaluate the critical temperature of the compounds Mn2SnS4. Our calculations show that taking into account the spin–orbit coupling has no significant effect on the accuracy of the band gap of Mn2SnS4. The calculated results of equilibrium volume, antiferromagnetic ordering type, local magnetic moment, and band gap are in good agreement with reported experimental results. The relative differences between spin configurations can be used to derive observables such as Curie-Weiss temperature (θ). The Curie-Weiss temperature is calculated using the mean-field approximation. Reasonable agreement with the experiment is found for all properties including the equilibrium volume, local magnetic moment, antiferromagnetic ordering type, band gap, and the Curie-Weiss temperature. [ABSTRACT FROM AUTHOR]

We demonstrate the peculiarities of the magnetization process in the ferrimagnetic intermetallic compound (Nd0.5Dy0.5)2Fe14B, which has been studied theoretically and experimentally using ultrahigh magnetic fields. We observe phase transition induced by external ultrahigh magnetic fields (up to 170 T) and also describe the magnetization process analytically in terms of critical transition fields. In this work, the first and second critical fields of the field-induced magnetic transitions, Hc1 and Hc2, were estimated, and the results were verified against experimental data for Hc1. Critical field Hc2 predicting the place of transition to the forced-ferromagnetic state was estimated for the first time for (Nd0.5Dy0.5)2Fe14B compound. A comparison of the magnetization behavior for (Nd0.5Dy0.5)2Fe14B with the basic systems Nd2Fe14B and Dy2Fe14B is also performed. We demonstrate that, in the Dy2Fe14B compound, the field-induced transition type is changed from the first to the second order due to the replacement of the Nd atom by Dy one.

Permanent magnets of varying shapes and sizes are increasingly produced. For hexaferrite magnets, it is challenging to incorporate polymers and a soft magnetic phase in the form of paste before injection molding or extrusion free-forming. In this study, hard magnetic barium hexaferrite/soft magnetic iron composites with a density of 2.28–2.34 g/cm3 are obtained after paste-injection molding and subsequent sintering at 1150 °C for 5 h. Variations of the binder (143.5–287.0 mg poly(vinyl alcohol), PVA) and the plasticizer (75–150 mg poly(ethylene glycol), PEG-400) in the ceramic–polymer paste give rise to comparable remanent magnetization (33.10–33.63 emu/g) and coercivity (3854–3857 Oe). Unlike all-ferrite systems, the presence of a soft magnetic metal phase is not detrimental to the coercivity. However, the remanent and saturation magnetizations are not substantially increased. The addition of 1% and 5% of iron oxide in the ceramic–polymer paste gives rise to hard/soft composites with lower densities of 2.11 and 2.14 g/cm3. The coercivity is increased to 3942–3945 Oe; however, the maximum energy product is reduced.

Layered Fe/MgO/Cr/MgO/Fe nanostructures are an artificial ferromagnetic material, in which the exchange interaction of the magnetic moments of the Fe layers through intermediate dielectric and metal layers can lead to magnetic configurations that are not implemented in well-studied Fe/MgO/Fe and Fe/Cr/Fe systems. The correlation between the structural and magnetic properties of layered nanoheterostructures Fe(10 nm)/MgO(1.5 nm)/Cr(t)/MgO(1.5 nm)/Fe(7 nm) (t = 0.9, 1.8 nm) is studied. The data of X-ray diffractometry and high-resolution reflectometry confirm the formation of an epitaxial crystal structure and reveal its layered nature with sharp interlayer boundaries. Vibration magnetometry does not reveal substantial differences in the hysteresis loops, which have a characteristic stepped shape. Polarized neutron reflectometry makes it possible to establish that the processes of magnetization reversal in these samples occur in different ways at the level of individual Fe layers. In the sample with Cr interlayers with a thickness of 0.9 nm, the Fe layers are exchange coupled through the MgO/Cr/MgO interlayer, and their rotation is correlated upon applying a magnetic field. There is no exchange interaction between the Fe layers in the sample with a Cr interlayer with a thickness of 1.8 nm, and they undergo magnetization reversal independent of each other. It is found that the magnetization reversal of the Fe/MgO/Cr/MgO/Fe systems is characterized by an intermediate state that can be controlled using a small external field with an intensity of several tens of oersted and a change in the orientation of the sample as well as by varying the thickness of the MgO layer. [ABSTRACT FROM AUTHOR]

A novel phenomenon of spontaneous positive exchange bias (PEB) is reported in SrFeO3−x/SrCoO3−x epitaxial bilayer without undergoing any magnetic field treatment. When inserting a thick SrTiO3 (STO) nonmagnetic spacer (about 6 nm) into the bilayer interface, this phenomenon still exists. Based on a series of testing means, the spontaneous PEB effect is supposed to be mainly related to short-range ferromagnetic (FM) exchange coupling at the interface when there is no STO spacer. As the STO interlayer reaches up to a certain thickness, short-range coupling interaction basically disappears. At this time, the long-range dipole field may be responsible for the coupling of the FM and antiferromagnetic (AFM) layer across the nonmagnetic STO and then leads to the same bias effect. Our discoveries provide a new way to realize and manipulate spontaneous exchange bias-based spintronics devices, such as magnetic recording heads and spin valves. [ABSTRACT FROM AUTHOR]

This paper studied the exchange coupling performance beside structural and microwave properties of SrFe12O19 (SFO) and x(CoTm0.01Tb0.01Fe1.98O4) (CoTmTb) (x ≤ 3.0) hard/soft ferrites nanocomposites (NCs). The structure and morphology of NCs were investigated by XRD, SEM, TEM and HR-TEM. Diffuse reflectance spectroscopic (DRS) measurements were applied on hexagonal ferrite, on spinel ferrite nanoparticles and on hard/soft NCs to specify the optical properties. Estimated Eg data are in a range between 1.32 and 1.79 eV. The magnetic properties were also inspected via measurements of magnetization (M) against magnetic field (H) at 300 K (RT) and 10 K (LT). The measurements performed at RT along with the plots of dM/dH versus H indicated that the NCs display good magnetic properties (exchange coupling behavior). The magnetic parameters such as (Ms, Mr, and Hc) show an enhancement in their values with an increasing the soft content at RT. Similarly, the maximum energy product (BH)max rises and reaches its max value for SFO/3(CoTmTb) NCs. Microwave properties of the SFO/x(CoTmTb) NCs were measured in the frequency range 33–50 GHz. From measured S11 and S21 parameters the main electrodynamic characteristics – permittivity and permeability (real and imaginary parts) were computed.

Magnetic spin exchange-coupled magnets have been investigated for obtaining an enhanced energy product, however, approaches at the nanoscale have been greatly restricted because of the lack of consideration of the relationships among the individual components. Here, we suggest a facile strategy for fabricating exchange-coupled nanomagnets with a large energy product. As a bottom-up approach, this work introduces a combined thermal decomposition and reduction/diffusion process to obtain a magnetic spin exchange coupled SmCo 5 /Co nanocomposite magnet. The SmCo 5 /Co nanocomposite magnet was fabricated through a three-step approach: (1) chemical synthesis of Co@SmO x nanoparticles and Co nanoparticles as hard and soft magnetic phases, respectively, (2) 3-dimensional alternating arrangement of both magnetic phases and (3) a reduction/diffusion process for the magnetic spin exchange interaction. Our results demonstrate that an effective magnetic spin exchange interaction strongly depends on the dimension and arrangement of the hard and soft phases, which were synthetically tuned to be within the magnetic domain wall size. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of half-Heusler alloys (HHAs) MnTiX (X = Si, Ge, Se, Te) are studied using full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k code which is a well-known code to investigate the physical properties of materials. The geometry optimization calculations for ferromagnetic (FM) and anti-ferromagnetic phases have been performed in order to determine the most stable phase of these materials. The results revealed that FM phase is the most stable, and further calculations (spin band structures and density of states) are carried for FM phase. The obtained results of band structures and density of states show that all considered alloys have half-metallic (HM) behavior with 100% spin polarization at the Fermi level. Furthermore, the exchange coupling of s-d and p-d exchange have also been discussed in detail for these materials. [ABSTRACT FROM AUTHOR]

Two novel dinuclear lanthanide(III) complexes were prepared with a triradical 2,4,6‐tris{p‐(N‐oxy‐N‐t‐butylamino)phenyl}‐1,3,5‐triazine (L), yielding [{LnIII(hfac)3(ethanol)(L)}2] (Ln2L2, Ln = Gd and La; hfac = 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dionate). Compound Ln2L2 has a cyclic structure in which two Ln ions are bridged by two triradical ligands. The cyclic dimers form quasi‐two‐dimensional (2D) structures via intermolecular hydrogen bonding and π‐π interactions. The La derivative, in which only L shows magnetic behavior, exhibits intraligand ferromagnetic and interligand antiferromagnetic 2 p–2 p couplings. Compound Gd2L2 shows ferromagnetic 4 f–2 p and intraligand 2 p–2 p couplings with a high‐spin state of S = 10. [ABSTRACT FROM AUTHOR]

Series of exchange-coupled BaFe12O19 (BaM)/CoFe2O4 (CFO) and BaM/Co0.5Zn0.5Fe2O4 (CZFO) composites were synthesized using the autocombustion method. Effect of soft (CFO/CZFO) phase weight fraction on structural, magnetic, and microwave properties of composites has been investigated and compared. X-ray diffraction patterns and scanning electron microscope (SEM) micrographs confirmed the presence of BaM and CFO/CZFO phases with well-distinguished grains in the composites. Existence of interfacial coupling was verified by smooth demagnetization behavior and single peak in corresponding $\text{d}M/\text{d}H$ curves. Saturation magnetization ($M_{s}$) and coercivity showed strong dependence on exchange interactions between hard and soft magnetic spins. Compared to BaM, $M_{s}$ of composites were 22% and 36% higher with CFO and CZFO, respectively. Frequency-dependent complex permittivity ($\varepsilon$) and permeability ($\mu $) in ${\text{K}}_{u}$ -band were found to be dependent upon the relative composition and nature of soft phase. Maximum $\varepsilon $ of 45 and $\mu $ of 1.6 were achieved for BaM/CFO (50/50) composite. Exchange-coupled magnetodielectric with high $\varepsilon $ and $\mu $ were developed for various microwave applications. [ABSTRACT FROM AUTHOR]

In order to obtain high magnetic properties in Ce–Pr–Nd–Fe–B spark plasma sintered (SPSed) magnets, the alloys were introduced by the dual-alloy method. The relationship of microstructure, magnetic properties, and thermal stability was investigated. The remanent magnetization, coercivity, and maximum energy product were sharply enhanced from 0.68 T, 653 kA/m, and 75.62 kJ/m3 to 0.80 T, 865 kA/m, and 104 kJ/m3 for the magnets that with 0 and 75 wt.% Pr–Fe–B addition. The Curie temperature also increased from 542 K to 563 K after adding Pr–Fe–B alloys. The scanning electron microscopy (SEM) analysis showed that, during the sintering process, the rare-earth elements migrated into the flake boundary and diffused in 2:14:1 main phases; thus, (Ce, Pr, Nd)2Fe14B hard magnetic phases were formed, which is helpful to optimize the microstructure and magnetic properties. An enhancement of exchange coupling among the grains of SPSed magnets was obtained as a result of grain refinement by adding Pr–Fe–B alloys. [ABSTRACT FROM AUTHOR]

In this study, [Co/Ni]2/PtMn thin films with different PtMn thicknesses (2.7 to 32.4 nm) were prepared on Si/SiO2 substrates. The post-deposition perpendicular magnetic field annealing (MFA) processes were carried out to modify the structures and magnetic properties. The MFA process also induced strong interlayer diffusion, rendering a less sharp interface between Co and Ni and PtMn layers. The transmission electron microscopy (TEM) lattice image analysis has shown that the films consisted of face-centered tetragonal (fct) PtMn (ordered by MFA), body-centered cubic (bcc) NiMn (due to intermixing), in addition to face-centered cubic (fcc) Co, Ni, and PtMn phases. The peak shift (2-theta from 39.9°C to 40.3°C) in X-ray diffraction spectra also confirmed the structural transition from fcc PtMn to fct PtMn after MFA, in agreement with those obtained by lattice images in TEM. The interdiffusion induced by MFA was also evidenced by the depth profile of X-ray photoelectron spectroscopy (XPS). Further, the magnetic properties measured by vibrating sample magnetometry (VSM) have shown an increased coercivity in MFA-treated samples. This is attributed to the presence of ordered fct PtMn, and NiMn phases exchange coupled to the ferromagnetic [Co/Ni]2 layers. The vertical shift (Mshift = -0.03 memu) of the hysteresis loops is ascribed to the pinned spins resulting from perpendicular MFA processes. [ABSTRACT FROM AUTHOR]

A new strategy to chemically synthesize exchange-coupled SmCo5/Sm2Co17 nanocomposites by in situ decomposition of SmCox (5 < x < 8.5) is reported in this work. Our synthesis starts with the fabrication of Co/Sm2O3 (Sm to Co atomic ratio of Sm/Co = 1:4.2), which can be reduced into 40-nm SmCo5 single crystal nanoparticles by Ca under the protection of CaO, showing a high coercivity of 2.85 T and saturation magnetization (Ms) of 0.0671 A·m2·g−1. By changing the Sm/Co to 1:4.5, 1:4.8 and 1:5.2, SmCo5/Sm2Co17 nanocomposites with different proportions were acquired using the same process. Owing to the in situ decomposition of SmCox intermediate, the small size (both of their size less than 10 nm) and uniform phase distribution were achieved in our nanocomposites. Thus, the as-prepared nanocomposites display a strong exchange-coupling interaction. As a consequence, SmCo5/Sm2Co17 (Sm/Co = 1:5.2) exhibits a coercivity of 1.23 T and enhanced M7T (magnetization at 7 T) of 0.0812 A·m2·g−1, increasing by 21% than pure SmCo5. Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites. The exchange-coupled SmCo5/Sm2Co17 nanocomposites with small size (both of their size less than 10 nm) have been chemically synthesized by in situ decomposition of SmCox (5 < x<8.5), which exhibits a coercivity of 1.23 T and enhanced Ms, increasing by 21% than pure SmCo5. [ABSTRACT FROM AUTHOR]

SrFe12O19/Zn0.4Co0.2Ni0.4Fe2O4 hard/soft ferrite composite particles with 20, 40, 60 and 80 wt.% of soft phase were prepared by one-pot sol-gel auto-combustion and physical mixing methods. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) were used to characterize the structural and magnetic properties of the samples. XRD spectrum revealed the formation of mixed ferrite phases in the composite particles. The hysteresis loops of the samples showed the presence of exchange coupling between the hard and soft ferrites. The composite particles with 20 and 60 wt.% of the soft phase demonstrated the highest Mr/Ms ratio, i.e. 0.29 and 0.28, respectively. In addition, the highest Ms, Mr and Hc were achieved in the composite particles with 40, 60 and 20 wt.% of the soft phase, respectively. Compared to the physical mixing method (PM), the composite particles prepared by the sol-gel auto-combustion method (OP) demonstrated better magnetic properties. The exchange coupling interaction between the hard and soft ferrite phases was similar in both methods. These composite particles exhibited magnetically single phase behaviour, however, the saturation magnetization was lower in the physical mixing pared to that of the one-pot method.

In this work, we perform a comparative study of the magnetization behavior of four series of compounds R2Fe14B and their hydrides R2Fe14BH5.5, and the compositions (Nd0.5R0.5)2Fe14B and their hydrides (Nd $_{0.5}\text{R}^\prime _{0.5})_{2}$ Fe14BH5.5 with R and $\text{R}^\prime =$ Ho, Er, and Tm. The magnetization is measured in pulsed magnetic fields up to 58 T and in megagauss fields up to 135 T at 5 K. The first and second critical fields of the field-induced transitions, $H_{c1}$ and $H_{c2}$ were estimated analytically and the results were verified against experimental data. We find that hydrogenation of R2Fe14B and (Nd $_{0.5}\text{R}^\prime _{0.5})_{2}$ Fe14B reduces drastically the $H_{c1}$ and $H_{c2}$ values and, as a consequence, the intersublattice R–Fe exchange interaction parameter $\lambda $. [ABSTRACT FROM AUTHOR]

We report on the results of investigations of the optical and magnetooptical properties of DyxCo1 –x/Bi/Py (Py is permalloy) trilayers. The temperature dependence of the magnetization has been examined using the magnetooptical Kerr effect and the optical refractive and absorption indices have been measured by spectral ellipsometry. It is shown that the thickness of the bismuth spacer affects the exchange coupling between the permalloy and DyCo layers, which manifests itself in the change in the magnetization compensation temperature and in the character of the exchange coupling. [ABSTRACT FROM AUTHOR]

In this paper, an exchange spring magnet with a new composition and improved magnetic performance was prepared and investigated. Accordingly, SrFe 12 O 19 /Co nanocomposite with various hard/soft magnetic phase ratios were prepared and inspected. Due to importance of particle size control in establishing full exchange coupling behavior and avoiding oxidation of cobalt nanoparticles, non-aqueous polyol method was exerted to prepare the nanocomposite. In order to investigate structural and morphological properties, X-ray diffraction and field emission scanning electron microscopy were employed and it was confirmed that polyol method performed well in size control and avoiding formation of impurities. Vibrating sample magnetometer was utilized for analyzing magnetic properties and single-phase magnetization behavior implied that nanocomposite components were appropriately exchange coupled. Investigations proved that nanocomposite with 15% mass ratio of soft phase demonstrated highest exchange coupling interactions. [ABSTRACT FROM AUTHOR]

The occurrence of ferro - and antiferromagnetism in Mn-Ni-Al alloys is governed by the sign of the direct exchange interaction between the Mn magnetic ions. Experimentally has been found that, if the separation between the Mn magnetic ions is greater than the critical value dcr= 2.91 Å, they are ferromagnetic and if the distance is less than the critical value, they are antiferromagnetic. The value of Mn local magnetic moment depends on the number of Al atoms in the first vicinity but the dominant factor is the Mn-Al distance. The nature of Mn-Mn exchange coupling was studied through X-ray diffraction, magnetic and XPS measurements. [ABSTRACT FROM AUTHOR]

Electrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare‐earth metals is an obstacle. Creating nanocomposites of rigidly exchange‐coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic‐phase material, is a promising route toward rare‐earth‐lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange‐spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random‐anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases. [ABSTRACT FROM AUTHOR]

The conducting oxide ferromagnets SrRuO3 (SRO) and La0.7Sr0.3MnO3 (LSMO) form a Ru exchange spring at a coherent low‐interdiffusion interface grown on TiO2‐terminated SrTiO3(STO)(001) substrates as SRO(d)/LSMO/STO(001) bilayers. Field‐ and temperature‐dependent magnetization data with systematically varied thickness d of SRO from 7 to 18 unit cells (uc) indicate a thickness of 10–14 uc of the exchange spring which governs magnetic switching and causes thickness‐dependent field‐cooling effects. Mn L3 edge X‐ray magnetic circular dichroism (XMCD) data reveal the dominating in‐plane orientation of interfacial spins. In low magnetic fields, noncoplanar, topologically nontrivial spin textures arise and can be switched, driven by the Zeeman energy of the LSMO layer. [ABSTRACT FROM AUTHOR]

Voltage‐driven oxygen ion migration in ferromagnetic metal/oxide heterostructures offers a highly effective means to tailor emergent interfacial functionalities. In heterojunctions with a core structure of Pt/Co/CoO/TiO2 (TaOx), it is demonstrated that exchange coupling of magnetic moments across the Co/CoO interface provides an extra source to stabilize the perpendicular magnetic anisotropy (PMA). Moreover, the strength of this interfacial coupling can be reversibly controlled through voltage‐driven oxygen ion migration at the Co/CoO interface, resulting in electrical‐field‐controllable PMA. In combination with the spin current generated from Pt, it is revealed that the spin‐orbit torque (SOT) switching of the perpendicular magnetization of Co can be turned ON/OFF by electrical field. Tunable PMA and SOT switching makes heavy metal/ferromagnetic metal/antiferromagnetic oxide heterojunctions a promising candidate to future voltage‐controlled, ultralow‐power, and high‐density spintronics devices. [ABSTRACT FROM AUTHOR]