Search

An amorphous GdFeCo film has a spin reorientation transition (SRT) with the temperature varying from 230 K to 300 K. Its magnetization reversal processes have been characterized by the hysteresis loops and first-order reversal curve (FORC) in the vicinity of the SRT temperature. Along with the SRT from out-of-plane to in-plane, the total irreversible components decrease with increasing temperature from 84% (250 K) to 13% (300 K) and the reversal process gradually changes from the pinning-type dominated reversal (250 K) to the nucleation type reversal (270 K), and then to the uniform rotation (300 K). The identification of the magnetization reversal process nearby SRT is important to understand the magnetic properties in the magneto-optical recording materials GdFeCo.

Soft magnetic composite material consisting of iron powder insulated by Ni-Zn ferrite nanofibres was prepared, where the nanofibres were bonded by the resin in various amounts in order to find the ratio for optimal insulation coating. The structure of material was documented and the magnetic and electrical properties were analysed. The optimal ratio of ferrite nanofibres to resin was found to be ½:½, as this sample exhibited the highest total and differential permeability, the lowest hysteresis and total energy losses and the highest number of active magnetic objects, found from the excess loss analysis, which revealed the highest proportion of domain wall displacements within the magnetization process. The magnetic properties values were reached better than for previous iron-resin composites. The relatively high real part of complex permeability was obtained together with its relatively high frequency stability. The optimal coating from ferrite nanofibres probably improved magnetic interaction between ferromagnetic particles by means of lowering inner demagnetizing fields.

Polyvinyl alcohol (PVA)-blended spinel phase NiNdxFe2-xO4 nanoferrites were successfully prepared with a different composition (x = 0.01, 0.03, 0.05, 0.07, and 0.09). The spinel cubic structure was revealed from X-ray diffraction pattern. These nanoferrites showed insulating behavior with an enhanced energy bandgap when compared with PVA-unblended nanoferrites. The obtained dielectric loss and real and complex dielectric constants were in the microwave region (frequency ∼2.9–5.95 GHz). Pseudocapacitance and resistive behavior were explored from impedance analysis. The magnetization hysteresis plot of nanoferrites showed a soft ferromagnetic nature. It was found that reduction in saturation magnetization of NiNdxFe2-xO4 nanoferrites obtained by PVA doping has the strong microwave absorption capacity.

Bundled cobalt ferrites (CoFe2O4) nanowires (BNWs) were successfully prepared by nanocasting pathway with ordered mesoporous SiO2 (SBA-15) templates. The well-dispersed CoFe2O4 nanowires (NWS) were separated from CoFe2O4 BNWs by centrifugal technology. Microstructure characterization indicated that CoFe2O4 BNWs and NWS possessed the same diameter and similar length. Thus, the influence of surface spins interaction between neighboring nanowires on the magnetic properties could be distinguished and discussed excluding the difference of morphology. Both samples presented ferromagnetism with the wasp-waisted hysteresis loops and the exchange bias effect was observed above 100 K. The surface spins interactions between the neighboring nanowires not only recombined the mismatch spins at the surface to form antiferromagnetic surface, but also inhibited the shape anisotropy of nanowires, leading to the decrease of saturation magnetization and coercivity of CoFe2O4 BNWs. The wasp-waisted hysteresis loops was attributed to the low temperature spin reorientation caused by the inclined spin on the surface of nanowires.

In this work, Ni-Co-Mn-Ti ferromagnetic shape memory alloy thin films, which consists of all 3d metals, are well prepared by direct-current (DC) double targets magnetron co-sputtering method. The deposition temperature (DT) dependence of microstructure and magnetic properties is studied in these thin films. The elemental compositions of these thin films are almost invariable, while the average grain size increases with the increasing DT. Micro-morphology shows that the crystal grains of films are spherical and homogeneous. For the samples deposited at 523 K and 573 K, an unusual magnetization reversal behavior is observed at ∼342 K and ∼225 K, respectively, in the thermomagnetic curves at the applied field μ0H = 1 T. Meanwhile, the hysteresis loops at ambient temperature demonstrate that in Ni-Co-Mn-Ti thin films the ferromagnetic contribution increases at the expense of diamagnetic one as DT increases. The reasons for these results are discussed.

Nanostructured ferromagnetic materials are applicable in a broad range of technologies, especially in the areas of data storage and spintronics. In addition, special structures are of high interest in basic research, aiming at understanding magnetization reversal processes on the nano-scale and thus possibly creating new applications. The strong influence of the shape anisotropy in magnetic nanoparticles enables tailoring magnetization reversal processes by the shape of such a particle. Typically, symmetrical structures are investigated, such as nano-dots, doughnuts, squares, rectangles, etc. Here we report on spiral nano-structures with constantly varying bending radii, modelled according to the Fibonacci spiral which is well-known from diverse plants and biological processes and also related to many mathematical problems. The magnetic Fibonacci nano-spirals with a thicker and a thinner lateral structure size as well as a mirrored form, building a heart-like shape, show large numbers of steps in the hysteresis loops, corresponding to stable intermediate states, due to nucleation and annihilation of domains which do not propagate along the spirals. The numbers of these stable intermediate states which could be utilized for data storage as well as the coercive fields depend strongly on the spiral dimensions and the orientation of the external magnetic field. Simulating minor loops showed the high stability of the intermediate states and thus underlined the possibility to use such structures for data storage.

Effects of disorder, frustration and low dimensional character occur in mixed magnetic Co1−xNixCl2·H2O, examined by dc magnetization and susceptibility measurements across the composition range. The pure components are quasi-one-dimensional antiferromagnets ordering at 15.0 K (Co) and 5.65 K (Ni), with susceptibility maxima at 16.2 and 8.4 K respectively; a spin glass transition also appears in the cobalt system near 8 K. In each compound weaker antiferromagnetic interchain exchange interactions supplement dominant ferromagnetic exchange along MCl2MCl2M… chemical and structural chains. High temperature magnetic susceptibilities are analyzed to yield Curie and Weiss constants in χM = C/(T − θ). Regular but not mean-field composition dependences appear for C and θ. The former is not linear and the latter displays a minimum near x = 0.30. Notable is a susceptibility maxima varying in location only weakly from x = 0.10 to x = 0.70, decreasing markedly only for higher x. Magnetization isotherms evolve regularly as x varies, with systematic composition dependences of a metamagnetic transition field and hysteresis through x = 0.70. A qualitative change in the isotherms occurs for x = 0.90, but substantial curvature still appears with smaller but definite hysteresis. A thermoremanent magnetization is seen in all mixtures, and is largest for the composition extremes. Thus, nonequilibrium magnetic behavior characteristic of the cobalt component, in contrast to the more conventional nickel component, occurs even when the latter is present in strong majority.

In this work, the (1 1 1)-oriented Fe3O4/BiFeO3 (BFO) multiferroic heterostructures were fabricated on the flexible muscovite (mica) substrate by magnetron sputtering. Hysteresis loops reveal the obvious exchange bias effect in the flexible Fe3O4/BFO heterostructures and demonstrate that this effect related to the coupling interaction at the interface between the Fe3O4 and the BFO. In the inward or outward bending heterostructures, the decrease of the exchange bias field (HEB) is resulted from the variation of the FeA3+−[O4]Fe3O48−−FeBFO3+ bond length and bond angle or/and the charge reconstruction effect of the Fe3O4 thin film in bending states. This exchange bias effect in the flexible Fe3O4/BFO heterostructures will contribute to the development of the next generation flexible storage device.

The Fe48Rh52 magnetic film with a thickness of 50 nm was grown on a piezoelectric substrate by magnetron sputtering. The chemical composition and crystalline structure were examined by energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. Two types of structural phases were detected: a bcc phase chemically ordered to the CsCl-type (B2 or α′) and an fcc γ-phase. Magnetic measurements of the FeRh film helped to observe an antiferromagnetic-ferromagnetic phase transition around 305 K (B = 0.1 T) in heating with a 27 K hysteresis, which is broader than in bulk alloys. A maximum of direct and converse magnetoelectric coefficients around the temperature of the antiferromagnetic-ferromagnetic transition was found during magnetoelectric measurements; they correlate with the results of magnetic measurements.

The hysteresis losses and their relation to the parameters of the minor static hysteresis loops were investigated in the nanocrystalline Fe67.5Co5Cu1Nb2Mo1.5Si14B9 alloy with magnetic-field-induced anisotropy. The analysis of experimental data was performed using a power function, which approximated the dependencies between the hysteresis parameters. It is shown that all the experimental dependences in cores with magnetic-field-induced anisotropy in a weak magnetic field are consistent with the formulas derived from the Rayleigh law. It is also shown, that in a nanocrystalline alloy with uniaxial induced anisotropy, certain empirical relationships obtained earlier for isotropic materials are not met, particularly, for the relation of the hysteresis losses to the remanence and the maximal magnetic induction. It has been found, that samples with longitudinal induced anisotropy demonstrate low initial permeability, and the magnetization process in the Rayleigh region is carried out by the domain walls’ displacement at distances comparable to the correlation length Lex. A magnetic hysteresis mechanism associated with the irreversible magnetization rotation in ferromagnetic clusters of nanocrystalline alloys is proposed. Formulas are proposed to calculate hysteresis losses in a soft magnetic nanocrystalline material with a different magnetic anisotropy.

Magnetization reversal and magnetic exchange coupling of (Co/Ni)×N/Ru/(Co/Pt)×12 were investigated as a function of the temperature. The number of repeats N of the soft multilayer (Co/Ni) was varied from 4 to 8 bilayers while the number of repeats of the hard bilayers (Co/Pt) was fixed to 12. Two steps hysteresis loops were observed for coupled structure with only 4 repeats of (Co/Ni) in a wide range of temperature (25–300 K). From the shift of the minor hysteresis loop, the antiferromagnetic exchange coupling Hex was measured and then the interlayer exchange coupling Jex was calculated. A non-monotonous dependence of Jex with temperature was observed for N = 4 with a maximum Jex of 0.13 erg/cm2 at 150 K. The annealing process performed on the same structure confirms the unusual behavior of interlayer exchange coupling Jex. As the repetition number N increases to 8 bilayers the two steps hysteresis loops disappeared in the investigated temperature range, however a small kink appeared in the range of 125 and 225 K for the case of 6 bilayers. From the analysis of the coupled and uncoupled structures, it seems that the dipolar energy overcomes the antiferromagnetic coupling for thicker (Co/Ni) multilayer.

Metal organic compound (C2H5NH3)2CuCl4 belongs to the family of layered perovskite multiferroic materials. It consists of ferromagnetic layers of corner sharing [CuCl4]2− octahedra connected by organic ions (two layers of [C2H5NH3]+). In this work we have studied magnetic properties of (C2H5NH3)2CuCl4 using SQUID magnetometer and AC susceptometer. Temperature dependence of magnetization showed existence of the antiferromagnetic transition at 10.2 K which changes to ferromagnetic with the application of moderate magnetic field. Near structural transition temperatures the anomaly of magnetization was observed. Hysteresis loops showed ferromagnetic behaviour for T T N and existence of anisotropy. Results of AC measurements showed no frequency dependence of the susceptibility and obtained temperature dependence of nonlinear susceptibility can be interpreted as a result of successive crossovers between different regimes.

The effect of hot deformation parameters on the magnetic properties of Mn51Al47C2 (at%) alloy was investigated. The hysteresis loops of cylindrical samples hot compressed to 50% of initial height at temperatures of 600 °C, 650 °C and 700 °C with strain rates 0.001 S−1 and 0.1 S−1 were obtained by means of vibrating sample magnetometer. In order to find the effect of strain on the magnetic properties, hot compressed samples to 30%, 45%, 60% and 75% in a specific temperature and strain rate were investigated. It was found that by increasing strain and strain rate, the coercivity increases and the highest coercivity gained at the temperature of 650 °C. Moreover, by further straining, the developed texture changed and higher remanent magnetization was obtained in axial direction for lower strains and in radial direction for higher strains.

Training is a common effect in exchange bias systems and accounts for the decrease of the exchange bias loop shift and coercivity with consecutively measured hysteresis loops until steady values. This is an ageing-like phenomenon that is related to the metastable state of the ferromagnetic/antiferromagnetic interface after field cooling. However, its origin still remains intriguing and not univoquely established. Here, by micromagnetic simulations considering discrete non-interacting antiferromagnetic grains embedded in a ferromagnetic matrix, it is demonstrated that the origin of training in granular Co-CoO exchange bias systems prepared by O ion implantation into Co thin films is linked to the perpendicular anisotropy of rotatable interface uncompensated spins. The simulations are compared to experimental data as reported in Physical Review B 89 (2014) 144407. The out-of-plane nature of the rotatable anisotropy of the system is also responsible for the magnetic reversal asymmetry between the first and the second magnetic reversals, evidencing the interconnection between training and magnetization reversal, suggesting that training effect and magnetization reversal asymmetry are ultimately interconnected through perpendicular anisotropy.

In this article, dynamic magnetic properties of La0.7Sr0.3MnO3 (LSMO) thin film capped with a Pb-free ferroelectric BZT-BCT layer deposited on two different substrates, i.e. lanthanum aluminate (LAO) and Platinum (Pt), by pulsed laser deposition (PLD) have been investigated using ferromagnetic resonance (FMR) spectroscopy. The heterostructures of BZT-BCT/LSMO on LAO substrate were highly (0 0 l)-oriented whereas these were randomly oriented on Pt substrate. The well-behaved M-H hysteresis loops were observed at room temperature for both heterostructures indicating the ferromagnetic behavior of LSMO. The right shift of the hysteresis loop of the heterostructure was observed due to the magnetoelectric coupling between ferroelectric and ferromagnetic layers. The FMR measurements yield optimum values of different important parameters such as the linewidth offset, Gilbert damping, gyromagnetic ratio, and in-plane uniaxial anisotropy field of the thin films, which are essential to design spin valve and magnetic tunneling based devices. We found the lowest Gilbert damping parameter of ∼0.03 for the BZT-BCT/LSMO/LAO heterostructure due to spin orbit coupling. In addition, the gyromagnetic ratio was also obtained to be small (0.002 GHz/Oe) in the same film. These results open new possibilities to use BZT-BCT/LSMO heterostructure for future spintronic device applications.

The adiabatic temperature change ΔTad of a Mn1:3Fe0:7P0:5Si0:55 Fe2P-type alloy was measured under different magnetic field-sweep rates from 0:93 Ts-1 to 2870 Ts-1. We find a field-sweep-rate independent magnetocaloric effect due a partial alignment of magnetic moments in the paramagnetic region overlapping with the magnetocaloric effect of the first-order phase transition. Additionally, the first-order phase transition is not completed even in fields up to 20T leading to a non-saturating behavior of ΔTad. Measurements in different pulsed fields reveal that the first-order phase transition cannot follow the fast field changes as previously assumed, resulting in a distinct field-dependent hysteresis in ΔTad.

Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan-like magnetic structure is described by two propagation vectors: k1 = 0 and k2 = 2π/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k2 vector does not change and is equal to k2 = 2π/c(0, 0, 0.027). An “incommensurate – lock-in” magnetic transition takes place at 8 K. The k2 vector exhibits a temperature hysteresis of about (5–6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k2 vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of ∼2 kOe, and the Tb-ion magnetic moment is equal to 8.3 μB. A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.

The effect of the interface anisotropy on the demagnetization progress and magnetic properties in Nd2Fe14B/α-Fe exchange-coupled multilayers with parallel crystalline anisotropy has been investigated within a micromagnetic framework. A set of equations satisfied by the angle between the magnetization and the applied field, as well as the formula for the nucleation field, have been derived analytically. The nucleation field goes up linearly with the interface anisotropy constants varying from −1 erg/cm2 to 1 erg/cm2 in a wide thickness range, with an amplitude up to 13%. The microscopic hysteresis loops, the evolution of the domain walls, the macroscopic demagnetization curves and the energy products are given by numerical calculations. The results indicate that the interface anisotropy affects not only the nucleation field and the maximal magnetic energy product, but also the pinning field or the coercivity. Positive interface anisotropy evidently enhances the pinning field or the coercivity, however, negative interface anisotropy obviously deteriorates the maximal energy product. These results suggest that a positive interface anisotropy should be preferred experimentally.

Coercivity mechanism has been studied intensively and debated for many years in magnetic materials, particularly in permanent magnets where defects play important roles in adjusting the coercivity. Such a role can be manifested in hard/soft multilayers, where the soft layer can be taken as an enlarged soft defect, which normally exists in so-called single-phased permanent magnets. In this paper, hysteresis loops and spin distributions have been obtained based on both three-dimensional (3D) and one-dimensional (1D) micromagnetic methods for SmCo/Fe to reveal the in-depth coercivity mechanism. Two different geometric models have been constructed to mimic the experimental trilayers, in one of which a transition layer between hard and soft layers is adopted, where calculated nucleation fields and coercivity match very well with the experimental data. As the soft layer thickness increases, both nucleation and coercive fields reduce whilst the coercivity mechanism changes from nucleation to pinning. Such a pinning is inherently related to nucleation and has both attributes of traditional nucleation and pinning, called as a hybrid coercivity mechanism here. The thickness-dependent coercivity mechanism obtained in this work agrees perfectly with the experimental data, which is general for all hard/soft composites and can be extended to single-phased permanent magnets where defects are inevitable.

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.

We successfully fabricated perpendicularly magnetized cobalt-ferrite Co x Fe 3 - x O 4 + δ (0 0 1) films on nonmagnetic metal TiN (0 0 1) films. We found that the in-plane lattice constant of the Co x Fe 3 - x O 4 + δ (0 0 1) films was larger than the out-of-plane lattice constant. This lattice strain induced perpendicular magnetic anisotropy, and square hysteresis curves were observed in out-of-plane magnetic fields for the Co x Fe 3 - x O 4 + δ (x = 0.4 ∼ 0.6) films. With the decrease of the Co composition from x = 1 to x = 0, the Co x Fe 3 - x O 4 + δ films approached not to conductive Fe 3 O 4 but to insulating γ - Fe 2 O 3 accompanying cation vacancies in the cubic spinel structure. The good tunneling conductivity character was observed for the Co x Fe 3 - x O 4 + δ tunnel junctions. The results open up a possibility that insulating Co x Fe 3 - x O 4 + δ films can be applied to elements of perpendicularly magnetized spintronics devices.

The preparation of magnetic nanotubes opens new avenues in nanobiotechnology as a consequence of their multiple properties embedded within the same moiety. Here, we report on synthesis and characterization of titanate nanotubes and their Fe-/Co-doped by means of X-ray diffraction, high-resolution transmission electron microscopy, and magnetic studies. Although the absence of 3d elements in Na2Ti3O7 nanotubes, our data for the first time, exhibits room temperature M−H hysteresis. Furthermore, our results show that the magnetization increased with Fe doping, while Co doping enhanced the coercivity. This behaviour was expected from the magnetic character of Fe and the positive magnetocrystalline anisotropy of Co. These results give access to the doping effect on tuning the properties of Na2Ti3O7 nanotubes.

Base on the Monte Carlo simulation and fast Fourier transformation micromagnetism (FFTM) method, the magnetic dynamic properties of defective Cobalt (Co) nanorings are studied. The simulated results indicate that the hysteresis loops of Co nanorings with small defect are similar to those of the symmetric nanorings. However, when the area of defect increases, the magnetization process of the defective Co nanorings is different from that of symmetric Co nanorings. It is found that the remanence (Mr) of the system increases at first and then decreases with the increase of defect location. Nevertheless, there is a relative stable region in which Mr almost do not change with the defect location varying when the defect is small. The simulated results are well analyzed through the evolution of spin-configurations (SCs) of the defective Co nanorings. The investigation about magnetic dynamic properties of the defective Co nanorings may provide reference for their application in high-density data storage.

We present the results of a detailed investigation of magnetism in spinel chromite NiCr2O4 magnetic nanoparticles (MNPs). Compared to the bulk NiCr2O4, the finite crystallite size of about 10 nm lowers the Jahn-Teller distortion and greatly enhances the collinearity of the spin structure in MNPs with considerably reduced “frustration index” = | θ CW | / T c . This leads to (longitudinal) ferrimagnetic ordering at much higher temperature, T c ≈ 100 K and suppression of (transverse) antiferromagnetic ordering in MNPs (cf. T c ≃ 65 K and T s ≃ 30 K in the bulk); a transition to the cluster spin glass state occurs at T g = 19.0 K. Moreover, the M-H hysteresis loops show anomalous “hour-glass” behavior at fields near H c in the vicinity of T g ; this non-monotonous H c (T) variation can not be accounted from the celebrated Stoner-Wohlfarth model. The present study interprets the anomalous H c (T) behavior in the framework of magnetically interacting core-shell structure with large surface anisotropy, and points out the importance of surface effects in nanochromites compared to their counterpart ferrites.

Modelling hysteresis behaviour is an essential task in transient analysis of electrical machines. A curve fitting approach based on isoparametric elements is proposed in this work. A hysteresis loop is split into sub-curves and each sub-curve has been modelled in terms of a second degree polynomial using three data points. Thus the model requires few data points to model a complete loop. The model equations can be easily derived using predefined shape functions of an isoparametric element without using any curve fitting algorithms. The proposed approach has been applied to model hysteresis data of two different materials, namely, grain-oriented (GO) laminations and soft magnetic composites (SMC). Symmetrical minor loops of GO materials with magnetization along any arbitrary direction are modelled for the first time. The calculated results are in close agreement with measured values. Compared to existing methods, the proposed technique in this paper is simple to understand and computationally efficient.

We conducted magnetization measurements on an S = 3 / 2 “breathing” pyrochlore antiferromagnet LiInCr4O8 in magnetic fields of up to 130 T using a coaxial-type magnetization pickup coil in a horizontal single-turn coil megagauss generator. The magnetization process exhibits a phase transition to a 1/2-magnetization plateau phase accompanied by a sudden increase in the magnetization with a discernible hysteresis at approximately 100 T. In addition, we also observed a shoulder-like behavior in the magnetization process prior to the 1/2-plateau phase, implicating the existence of a novel magnetic phase, peculiar to the “breathing” pyrochlore antiferromagnet.

The Co1−xMnx (9.1 ≤ x ≤ 15.2) alloy nanowires with uniform size and high density have been prepared by AC electrodeposition method into the anodized aluminum oxide AAO templates by using the different AC potential from 9 V to 13 V. A systematic study has been done about the voltage dependent physical, dielectric and magnetic properties of CoMn nanowires. The diameter and length of nanowires is found to be 95 nm and 15 μm respectively by getting the image from Secondary Electron Microscope. The Energy Dispersive X-ray Spectroscopy gave the information which shows that the composition of Mn and Co increases and decreases respectively with the increase of deposition voltage. It was observed from X-ray Diffraction data of all samples that CoMn alloy nanowires have the cubic structure and crystallite size vary from ∼39.6 nm to ∼48.9 nm. The Fourier Transform Infrared Spectroscopy pattern shows the presence of other materials such as CoO, MnO, and Al2O3 at different wavenumber range. The dielectric constant, dielectric loss, tangent loss and AC conductivity have been measured from LCR meter data at room temperature. The aforementioned dielectric properties decrease with the increase of deposition voltage due to incorporation of Mn ions and deduction of Co ions. The descending trend of AC conductivity against the increasing voltage is also due to the increase of grain boundary volume. The M-H loops of CoMn nanowires have been measured by using the Vibrating Sample Magnetometer and show the anisotropic and ferromagnetic behavior. From hysteresis loops, it is also found that magnetization reversal has nucleation mode and squareness decreases with increase of angle. The effective anisotropy is found to be along the nanowires. This study is useful to modify the physical, structural, dielectric and magnetic properties of the metallic materials according to desire devices.

Asymmetric magnetization reversal in perpendicularly exchange biased Pt/Co/Pt/IrMn multilayers was studied in nanometer scale by non-contact magnetic force microscopy with variable highly localized bipolar magnetic fields of the MFM tip. The hysteresis process of domain nucleation and pinned domain wall motion has been triggered and mapped simultaneously through MFM. Unstable magnetization reversal of submicron domains has been directly observed as well as exchange bias induced asymmetry in the depinning fields for domain wall motion. The current results demonstrated a possible way to locally mapping and manipulating novel magnetic nano-structures such as vortices and Skyrmions.

This paper highlights the experimental study of Ce3+ ions doped M-type hexaferrite Sr1−xCexFe12O19 (0.00 ≤ x ≤ 0.30) prepared by adopting the conventional ceramic process. The M-type hexagonal structure is confirmed in the X-ray diffraction measurements. There were two phases recognized for the magnetic powders with varying Ce content, one in-between x = 0.00 to 0.20 as a single magneto plumbite segment and the other at x ≥ 0.20 as a second phase or the so called α-Fe2O3 phase. The micrographs of the sintered magnets depicted hexagonal crystal shapes. For magnetic properties a systematic study was done on the room temperature B–H hysteresis measurements. The estimated remanence value first increases with x in the range of x = 0.00 to 0.15 and then showed a decrease at x ≥ 0.15. Besides, the intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) show decreasing-increasing character while maximum energy product (BHmax) and ratio Hk/Hcj demonstrate increasing-decreasing character in the Ce doping range x of x ≤ 0.15 and x > 0.15 respectively.

In this study, we precisely calculated the specific loss powers (SLPs) of magnetic nanoparticles (MNPs) based on dynamic hysteresis measurements. The advantage of this evaluation method is that the intensity and frequency of the applied magnetic field can be varied over a wide range for samples of various condition. The results show that the coercive field and SLP of Resovist® increase by orienting the magnetic easy axes of the nanoparticles. The magnetic field was applied either parallel or perpendicular to the nanoparticle orientation. The area enclosed by the dynamic hysteresis curve was larger when the AC field was applied parallel to the nanoparticle orientation, indicating a greater increase in the hyperthermia temperature. This characteristic originated from the magnetic anisotropy energy of the nanoparticles and is in good agreement with our simulational results. The SLP of a solid sample with an aligned easy axis measured under an AC field of 4 kA/m, which was applied parallel to the axis, was more than two times that of a liquid sample. We also evaluated the SLPs of superparamagnetic 4-nm-diameter γ-Fe2O3 and ferromagnetic 20–30-nm-diameter Fe3O4 MNPs and compared them to that of Resovist®.

Specific loss power has been measured on γ-Fe 2 O 3 nanoparticles dispersed in water by means of several techniques, i.e. heat flow in a calorimeter, hyperthermia, and static and dynamic hysteresis loops. Static hysteresis loops as a function of the maximum applied field underestimate the power losses as dynamic effects are not exploited, but turned out to be a valuable tool to prove the consistency of specific loss power measurements obtained by the other techniques over a wide range of applied magnetic field intensities. A temperature-dependence of the specific loss power has been taken into account in hyperthermia measurements performed with a fully modelled non adiabatic experimental setup. Simple mean-field theoretical models (interacting superparamagnetic, modified Stoner-Wohlfarth) have been exploited to reproduce the static energy losses of the particles. © 2018 The Authors This work was supported in part by Russian Science Foundation grant 18-19-00090 This work was funded in part by the EMPIR program co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation program, project 16NRM044 “MagNaStand”.

Finite element micromagnetics are used to simulate remanence, hysteresis and dynamic switching in crescent shaped permalloy caps, a geometry that corresponds to either normal or oblique deposition of films on nanosphere arrays. Oblique deposition breaks the symmetry and favours onion states rather than vortices. It introduces in-plane shape anisotropy analogous to that of an elongated island and increases the in-plane coercivity. In isolated caps, the critical diameter above which the vortex state is the minimum energy state, is D = 123 nm for angles below θ = 20 deg. It increases with θ up to a vlaue of D = 157 nm at θ = 45 deg. Even for sizes for which the onion state is the lowest energy state, vortex states can be stabilized in isolated caps but the interparticle magnetostatic interactions tend to destabilize them driving the system to its ground state. The switching field of onion states can be reduced by 36% using microwave resonance at frequencies approaching the resonant (Kittel mode) frequencies.

The magnetization of a magnetoactive elastomer (MAE) with microparticles of soft magnetic carbonyl iron embedded in a highly elastic matrix has been studied. It is shown that at high temperatures its magnetization curve has the form of a specific hysteresis loop. This hysteresis is attributed to the influence of displacement of magnetized particles in the elastically soft elastomer matrix under the effect of magnetic forces, leading to the change of magnetic interaction between the particles. In this case, there is a maximum in the field dependence of the magnetic susceptibility, the occurrence of which has been associated with the competition between re-arrangement of particles, when they are displaced in a magnetic field, and saturation of particles’ magnetization. When the MAE is cooled below approximately 225 K, both the magnetic hysteresis and the maximum in the field dependence of the magnetic susceptibility disappear. When the MAE material is cooled below the solidification temperature of the elastomer matrix, the displacements of the magnetic particles during magnetization are blocked by the rigid matrix. The magnetization reversal of the MAE is reversible. This means that the shape of subsequent magnetization loops remains constant and the sample returns into the initial non-magnetized state after the magnetic field is turned off.

The M-H hysteresis curves of field cooled CoFe/FeMn bilayers and CoFe/FeMn/CoFe trilayers were studied to understand the exchange bias phenomena in these systems. The measured data revealed that the values of the exchange bias corresponding to a bottom CoFe layer reduced by about 23.5% with an addition of another CoFe layer at the top of bilayer stack. It was also observed that, while this reduction in exchange bias of a bottom CoFe layer (calculated in %) depends on thicknesses of a top CoFe layer and an antiferromagnetic FeMn layer, it is independent of the thickness of bottom CoFe layer. As the strength of exchange bias depends on the presence of pinned uncompensated moments in an antiferromagnetic layer, our observations indicate that the FeMn layer consists comparatively lower amount of pinned uncompensated moments in trilayers. This reduction in pinned uncompensated moments of FeMn layer in trilayers is then co-related with the domain wall suppression in the FeMn layer in CoFe/FeMn/CoFe trilayers.

Applicability of the Maxwell relation (MR) to the magnetocaloric effect (MCE) of ferromagnets with the first order transition (FOT) is studied by comparing the MCEs obtained without and with the aid of the MR. For this purpose, we first introduce a phenomenological free energy which gives the FOT of the ferromagnetic system, on the basis of which temperature T- and magnetic field H-dependences of the magnetization, and the magnetic phase diagram in the T - H plane are described. This free energy is also used to derive the entropy change induced by H , Δ S ( H ) , without the aid of the MR. This entropy change Δ S ( H ) judges those obtained with the aid of the MR in the subsequent calculations. The a priori application of the MR to the MCE of ferromagnets with the FOT, where the MR is treated as done on ferromagnets with the second order transition, is simulated by substituting the calculated magnetization into the MR. The MCE obtained by this a priori application of the MR is shown to exhibit its insufficient agreement with the MCE without the aid of the MR. Especially, the steeple-like shape of the T-dependence of the entropy change and its maximum value going to 0 at H → 0 are ascribed to the a priori application of the MR. On the other hand, the straight application of the MR is confirmed to successfully produce Δ S ( H ) without the aid of the MR also in the case of the FOT ferromagnet. The MR is extensively applied to analyses of the MCEs of ferromagnets which exhibit hysteretic phenomena around the FOT. Even in the presence of the hysteresis in a narrow region around the FOT, the analyses by use of the MR are shown to produce the maximum value of the entropy change and the adiabatic transition temperature change which are close to those in the absence of the hysteresis. Finally, careful numerical calculations in using the MR are also described.

Co2W-type hexaferrite nanoparticles with composition of SrCo2−x(MnZnCa)x/3Fe16O27(x = 0–0.5) were synthesized by a co-precipitation method. The synthesized nanoparticles were decorated on the outer surface of multi-walled carbon nanotubes by chemical method. X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry, magnetic susceptometer and vector network analyzer were utilized to characterize the structural, magnetic, and reflection loss properties of the nanocomposites. The structural results showed a perfect diffusion of Mn, Zn and Ca ions into the crystal structure of Co2W hexaferrite without forming any secondary phases. The SEM images provide clear information about the size of nanoparticles (50–85 nm) through these samples. The hysteresis loops showed hard magnetic property with enhanced coercivity which reflects that the synthesized particles have almost high magnetic anisotropic field, well suitable for absorbing materials. The coercivity (Hc) increased from 1450 Oe at x = 0.0, to 1650 Oe at x = 0.3, and then decreases to 1320 Oe at x = 0.5. High reduction in the coercivity was detected consistent with the large particle sizes for these samples. Ferrite nanoparticles were decorated on the surface of carbon nanotubes in almost constant distance. The interacting mode was confirmed between magnetic nanoparticles by means of plotting real and imaginary parts of magnetic susceptibility versus temperature at various frequencies. Based on reflectivity measurement, the sample with x = 0.3 showed a maximum reflection loss of −37 dB at the frequency of 9.4 GHz. This sample revealed the best performance with low reflectivity and high absorption broadband (4 GHz) at X-band frequency range.

We discuss ways of an improvement of the analytic technique for characterization of magnetic nanoparticles and their chemical transformation to ferritin-like forms after their injection in a living organism by means of measuring and analyzing the Mossbauer spectra and magnetization curves. This is based first on the theoretical achievements in developing models of magnetic dynamics of antiferromagnetic nanoparticles for describing thermodynamic properties of ferritin and related proteins. Generalization of the approach for ferrimagnetic nanoparticles allows one to take directly into account the magnetic nature of nanoparticles in analyzing the corresponding experimental data. Another way is to extend this technique with measuring and analyzing non-equilibrium magnetization curves (hysteresis loops) which allows one to more reliably evaluate time changes in the residual nanoparticles and iron-containing proteins characteristics during biodegradation.

The magnetic properties of non-grain-oriented (NO) electrical steels are a direct product of their inherent material properties in combination with induced changes due to material processing and external operational conditions such as magnetization and frequency. Chemical composition, grain size and texture are elementary intrinsic factors which determine the magnetic properties. Focus of this study is to improve the understanding of grain size and texture as important factors that affect different loss-components. A strong focus is placed on the frequency dependence and concurrent loss component distribution over application relevant frequency ranges of electrical machines. Due to its impact on the eddy current losses as well as the hysteresis components, the final thickness is additional subject of this study. A total of seven materials are produced on an experimental production line from one alloy. By different production and processing steps, different grain structures, textures and final thickness are achieved. The changes in the materials are attributed to the process variations and magnetically characterized. A loss separation procedure as well as loss modeling is performed and discussed. This work is part of a research field which aims to improve parametric models with low additional computational effort for the numerical simulation of electrical machines. The goal is to improve the accuracy of models with a deeper understanding of the material science.

The regular shape of the magnetoresistance as a function of applied magnetic field, R(H), is important for numerous spin valves applications. Nevertheless, in many practical studies the shape of the R(H) curve is unpredictably complicated. We draw attention to the close connection between R(H) and magnetization hysteresis loop and propose a simple technique, which allows interpreting the R(H) features and calculating R(H) curves from known hysteresis loops of ferromagnetic layers, composing spin valves. And vice versa, the shape of the hysteresis loops of the composing ferromagnetic layers can be obtained from R(H) curves. The method is suitable for prompt selection of promising spin valve stacks.

Low dimensional artificially engineered spintronic materials can be used to increase the density of magnetic media using energy based magnetic recording. For this purpose, magnetic nanostructures such as patterned arrays with magnetic characteristics having high uniaxial magnetic anisotropy are the new contestants in the field of ultrahigh storage media. In this context, we focus on the synthesis of nano-dimensional magnetic media consisting of Dy and Fe bilayer structured arrays, fashioned in patterned magnetic nanostructures. The dimensional characteristics of these nanostructures were illustrated using field emission electron microscopy and energy dispersive elemental mapping. Room temperature magnetic properties of these nanostructures were first determined through atomistic spin model simulations which led us to configure the experimental hysteresis loop for DyFe bilayer. The deposition of crystalline Dy and Fe through DC and RF sputtering resulted in a soft magnetic behavior as revealed by the characteristic shape of the hysteresis loops exhibiting anisotropic features. Reflection spectra for these DyFe bilayers reveal a decrease in reflectance from ultraviolet to visible region demonstrating high absorption in visible region. The variation in reflectance spectra and squareness of the hysteresis loop reveals that these nanostructures as a viable candidate for magneto-optical devices.

Applying Monte Carlo simulation, the critical and compensation behaviors of a graphyne bilayer are explored in this study. The effects of the crystal field and exchange coupling on the magnetic behaviors and the phase diagrams are presented in detail. The results show that the critical temperature increases as the crystal field decreases or the exchange coupling increases. In addition, the double compensation points can also be found in this system. Furthermore, we give the hysteresis loops under different parameters, and the multi-loop hysteresis behaviors are observed.

The magnetism of layered NaxMnO2 with space group P63/mmc is investigated by first-principles calculation and magnetic measurement. Results indicate that NaMnO2 without any Na-vacancies posses the antiferromagnetic metal state. And along with Na-vacancies formed, the magnetism and electronic properties of NaxMnO2 show rich change, which undergo the change of AFM → FM → AFM and metal → semiconductor, respectively. Magnetic measurement of Na0.806MnO2−δ with space group P63/mmc also shows that have thin hysteresis and remanent under 5 K. Hence, Na0.806MnO2−δ presents the ferromagnetic metal state under low temperature rooting in the Mn3+-O2−-Mn4+ double exchange, which is agreement with theoretical results.

Non-oriented electrical steel is widely used in the manufacturing of motor stators. The magnetic property will be influenced by the residual stress induced from manufacturing processes. The classical Jile-Atherton hysteresis model with constant parameters is widely used to describe the magnetization characteristic of ferromagnetic materials. In the model, the parameter a represents the domain density, k is the pinning factor reflecting the strength of the pinning effect, α is the domain coupling parameter affecting the slope of the mid-segment of the hysteresis loop and C is the coefficient of reversibility. However, all the four parameters are influenced by residual stress. Furthermore, the influence of magnetic peak induction on parameters can’t be ignored according to our work. The classical Jile-Atherton hysteresis model cannot reflect the influence of residual stress and magnetic peak induction. In this paper, a modified residual stress dependent Jile-Atherton hysteresis model was proposed, whose parameters are extended to functions related to residual stress and magnetic peak induction. A novel device was designed to carry out magnetic property testing experiments under large stress. The parameters were identified by a MATLAB program and the influence of residual stress and magnetic peak induction was analyzed. The accuracy of parameters was validated by experiments, which showed that the modified model worked well in describing the magnetization characteristic under different stresses and magnetic peak inductions. This could provide some guidance for the manufacturing processes of motor stators.