Tailoring of Magnetic Properties of Magnetostatically-Coupled Glass-Covered Magnetic Microwires

We report on tailoring of magnetic properties of Fe- and Co-rich microwires through magnetostatic coupling among them. We studied hysteresis loops of the arrays containing different number of the Co₆₇Fe_3.9Ni_1.5B_11.5Si_14.5M_0.6 and Fe₇₄B₁₃Si₁₁C₂ amorphous microwires. Fe₇₄B₁₃Si₁₁C₂ microwires have rectangular hysteresis loop, while Co₆₇Fe_3.9Ni_1.5B1_1.5Si_14.5M_0.6 with vanishing magnetostriction constant posses inclined hysteresis loop with low coercivity. The presence of neighboring microwire (Fe either Co-based) significantly modifies hysteresis loop of whole microwire array. In a microwire array containing Fe-based microwires, we observed splitting of the initially rectangular hysteresis loop with a number of Barkhausen jumps correlated with number of Fe-rich microwires. In Co?CCo arrays, we observed a change of inclination of overall hysteresis loop, and consequently magnetic anisotropy field under influence of the additional of Co-based microwire. In the case of mixed arrays containing Fe and Co-rich microwires, we were able to obtain irregular hysteresis loops with unusual shape. In this case, considerable increase of harmonics has been observed. Magnetic field amplitude and frequency affect the behavior of all studied arrays. Increasing the amplitude the shape of hysteresis loop of microwire array containing Fe-based microwires transforms from multi-step to single above certain magnetic field amplitude. In the array with Co-based microwires, we observe a change of coercivity. Observed dependences have been attributed by us to the magnetostatic interaction between the microwires with different magnetic domain structure. Together with the conventional method, such as thermal treatment, designing of arrays containing different types of microwires can serve for tailoring of their magnetic properties.     

Role of Defects on Domain Wall Propagation in Magnetically Bistable Glass-Covered Microwires

We are trying to reveal the contribution of local defects on DW propagation in amorphous microwires. Consequently, we present a comparative study of single domain wall dynamics and local nucleation fields in Fe- and Co-rich amorphous glass-coated microwires. For this we modified experimental set-up based on the classical Sixtus?CTonks approach introducing additional pick-up coil in order evaluate defects contribution in domain wall propagation. Below some critical magnetic field, H _N , determined by the microwires inhomogeneities, an almost linear DW velocity,?v, dependence on magnetic field, H, is found. Quite fast DW propagation (v?till 3000?m/s at?H about 65?A/m) has been observed. When the applied magnetic field exceeds H _N , new reverse domains can be nucleated and consequently tandem remagnetization mechanism can be realized. The role of defects existing in magnetically bistable microwires is related with nucleation of new reversed domains.     

Magnetoelastic properties of an amorphous ferromagnetic alloy annealed by electric current

The magnetoelastic wave propagation velocity and the magnetic-field-induced change in the elastic modulus (ΔE effect) have been studied as functions of the magnetic field strength in thin stripes of an amorphous ferromagnetic alloy (Fe₆₄Co₂₁B₁₅) annealed by direct electric current of variable density. It is shown that such treatment is an effective method for obtaining amorphous ferromagnetic alloy ribbons with uniaxial anisotropy and high magnetoelastic characteristics.     

Remagnetization of a circularly anisotropic amorphous wire in an alternating magnetic field

Remagnetization of an amorphous ferromagnetic wire with circular anisotropy in an alternating longitudinal magnetic field was theoretically studied within the framework of a quasistationary approximation. A frequency spectrum of the emf generated in a probing coil wound on the wire was determined, and analytical expressions describing the dependence of the emf amplitude on the alternating magnetic field amplitude H ₀ and the constant magnetic bias field value H _e were derived. The results can be applied to the development of weak magnetic field sensors.     

Anisotropic effects in the magnetoelastic damping of electrolytic nickel in a direct magnetic field

In the present work a quantitative study of the dependence of the e.m.f. U_W induced in a search coil which surrounds a ferromagnetic sample performing torsional oscillations at a constant amplitude on the amplitude and the frequency of the oscillations is made. The dependence of U_W on the intensity of the longitudinal magnetic field H is also studied. On the basis of these studies experimental arguments are presented for the existence of magnetoelastic hysteresis and macro-currents. A supplementary mechanism through which the energy of the vibrating system can be dissipated is also presented.     

Small-Angle Neutron Scattering by the Magnetic Microstructure of Nanocrystalline Ferromagnets Near Saturation

The paper presents a theoretical analysis of elastic magnetic small-angle neutron scattering (SANS) due to the nonuniform magnetic microstructure in nanocrystalline ferromagnets. The reaction of the magnetization to the magnetocrystalline and magnetoelastic anisotropy fields is derived using the theory of micromagnetics. In the limit where the scattering volume is a single magnetic domain, and the magnetization is nearly aligned with the direction of the magnetic field, closed form solutions are given for the differential scattering cross-section as a function of the scattering vector and of the magnetic field. These expressions involve an anisotropy field scattering function, that depends only on the Fourier components of the anisotropy field microstructure, not on the applied field, and a micromagnetic response function for SANS, that can be computed from tabulated values of the materials parameters saturation magnetization and exchange stiffness constant or spin wave stiffness constant. Based on these results, it is suggested that the anisotropy field scattering function S_H can be extracted from experimental SANS data. A sum rule for S_H suggests measurement of the volumetric mean square anisotropy field. When magnetocrystalline anisotropy is dominant, then a mean grain size or the grain size distribution may be determined by analysis of S_H.     

Correlation Between Magnetoresistance and Magnetization Hysteresis in a Granular High-T C Superconductor: Impact of Flux Compression in the Intergrain Medium

The correlation between experimental magnetic field dependences of magnetoresistance and magnetization hysteresis in granular YBa₂Cu₃O₇ is established. Within the proposed approach, magnetoresistance is assumed to be determined by the effective field in the intergrain boundaries the ensemble of which is considered to be a Josephson medium. The effective field in the intergrain medium can be written in the form B _eff(H)=H?4πM(H)×α, where α is the parameter of averaged demagnetizing factors of grains and the degree of flux compression. A comparison of experimental magnetoresistance R(H) and magnetization M(H) hysteresis dependences obtained at different external magnetic field sweep rates yields the value α～10, which is caused by the flux compression between grains. The proposed model describes well most of the features of the magnetoresistance hysteresis in granular high-T _C superconductors.     

Magnetic, Electrical and Thermodynamic Properties of UCuT x Al11−x Alloys Where T = Mn, Fe and x=4 and 5

The structure, magnetic, electrical, and thermodynamic properties of UCuT _x Al_11?x alloys, where T = Mn or Fe and x=4 or 5 are presented. The behavior of the Fe alloys is ferromagnetic-like with the Curie points amounting to 180 and 230 K, and the saturation magnetic moments under magnetic field of 5 T equal to 4.75 and 6.02 μ_B/f.u., respectively, whereas under a magnetic field of about 34 T the magnetic moments amount to 6.9 and 9.0 μ_B/f.u. for the alloys with x=4 and 5, respectively. The Curie points are reflected in the temperature dependence of the specific heat in which the anomalies are found at 180–200 and 230 K for alloys with x=4 and 5, respectively, however, it shows no reflection in the temperature dependence of the electrical resistivity. The field dependence of the magnetization at T=1.9 K for both compounds exhibits considerable hysteresis. There is a pronounced difference between ZFC and FC magnetization in its temperature dependence below the Curie point for materials with x=4 and 5. The Mn alloys exhibit ferrimagnetic-like character for which, supposedly, the interplay of the uranium and manganize sublattices is responsible. Magnetic transitions are determined at T _N =300 (x=4) and 380 K (x=5). However, those anomalies do not find confirmation in the temperature dependence of the specific heat and the electrical resistivity. Magnetic moments determined at T=1.9 K and in a magnetic field of 5 T are very low and in both cases amount to about 0.35 μ_B/f.u. and these values are slightly higher in a magnetic field of 34 T reaching a value of about 1.5 μ_B/f.u. Also for the Mn alloys the clear difference between ZFC and FC magnetization in its temperature dependence below the Curie point is observed.     

Random Magnetic Anisotropy Studies in SmCo<Subscript>5</Subscript> Thin Films

SmCo₅ thin films with different thicknesses were prepared by electron beam evaporation on Kapton substrates. The out-of-plane hysteresis loops for different thicknesses reveal a maximum coercive field when the thickness is 15 nm. Using random magnetic anisotropy model, the thickness dependence of magnetic properties was studied in SmCo₅ nanocrystalline films and several fundamental magnetic parameters were extracted. We have determined the local magnetic anisotropy constant K ₁ which is found to increase with increasing film thickness except for t =?7 nm which is thought to arise from the structural imperfection of the SmCo₅ films.     

Epitaxial Orientation and Planar Hall Effect for MnAs Films Grown on GaAs(001)

We study the planar Hall effect in high quality thin ferromagnetic films of MnAs grown on GaAs(001) exhibiting hysteresis due to the hindered rotation of the magnetic moment in the plane. The saturation magnetic field H _s, which is necessary to align the magnetization along the hard axis, depends sensitively on the epitaxial orientation of the film. By using out-of-plane magnetic fields directions, we show that H _s is strongest along the direction of the c-axis of the MnAs crystal, thus demonstrating the importance of the crystal field anisotropy for the planar Hall effect.     

Effect of tensile stresses on the magnetoelasticity of Fe<Subscript>64</Subscript>Co<Subscript>21</Subscript>B<Subscript>15</Subscript> ferromagnetic ribbons

The effect of constant tensile elastic stresses on the field dependence of the magnetoelasticity (ΔE effect) of Fe₆₄Co₂₁B₁₅ amorphous ferromagnetic ribbons after thermomagnetic treatment in a temperature interval from 290 to 360°C has been studied. The maximum value of the negative ΔE effect increases upon application of a relatively small tensile stress and decreases under the action of large stresses. In addition, the application of tensile stresses decreases the magnetic field corresponding to a maximum negative ΔE effect. The results are explained based on notions about the influence of constant tensile stresses on the domain structure of ferromagnetic materials with positive magnetostriction and induced uniaxial anisotropy.     

Double Hard Axes of Hysteresis Loop in Wide-Angle Obliquely Sputtered CoFeB Amorphous Films

Soft magnetic Co₄₀Fe₄₀B₂₀ films with different tilt angle were successfully deposited on silicon substrates by using oblique sputtering technique. Different oblique angles are achieved by controlling the position of samples. The corresponding static magnetic properties of these samples were then systematically investigated. Interestingly, with the oblique angle increasing from 38° to 55°, the MOKE hysteresis loop of the thin films displays a unique and special performance with double hard axes. Meanwhile, despite of the measurement magnetic field along PR or AR direction, both of the hysteresis loops have two-stage magnetization reversal that means there are two comparably strong anisotropies in the CoFeB films. Moreover, rotating samples from in-plane to out-of-plane, the hysteresis loops demonstrate the perpendicular anisotropy exist in CoFeB films. The cross-section SEM characterizations further verify that the residual field from the magnetic cylinder will strongly impact the microstructures of thin film.     

Fe<Subscript>78</Subscript>Si<Subscript>9</Subscript>B<Subscript>13</Subscript> amorphous powder core with improved magnetic properties

The effects of pre-annealing treatments on the soft magnetic properties of the corresponding Fe₇₈Si₉B₁₃ amorphous powder cores were investigated. The amorphous powder cores prepared from pre-annealed powder have better soft magnetic properties compared with unpretreated powder core in the as-cast state. The result shows that the powder after pre-annealing in a magnetic field presents a regular domain structure and the soft magnetic properties of the corresponding powder cores are greatly improved. As the result, the magnetic-field annealed powder core has the highest effective permeability (μ _e) of 37, which is 23 % higher than the as-cast one and 7 % than only vacuum-annealed one. The total core loss (P _cv) for the core annealed in magnetic field is only 141 W/kg (100 kHz, 50 mT) and as low as 36 % of the P _cv for the powder core in the as-cast state. The one annealed in magnetic field also exhibits the best DC bias properties of 92 %. This work provides a novel approach to realizing low P _cv and high μ _e for Fe₇₈Si₉B₁₃ powder cores and also validates the application prospect of powder cores in the work condition of different ripple currents, different loads and a wide frequency (f) range (10 kHz–10 MHz).     

High-Field ESR and Magnetization Study of a Novel Macrocyclic Chelate Trinuclear Ni(II) Complex

We have investigated magnetic properties of a novel macrocyclic chelate Ni(II) complex [Ni₃(L)(OAc)₂], by means of the static magnetization M and high field frequency tunable electron spin resonance (HF-ESR). Magnetic field B dependencies of M reveal the magnetic ground state with a total spin S $^{\mathit{tot}}_{0}=1$ and a strong antiferromagnetic coupling between three Ni(II) ions. HF-ESR measurements at frequencies ν=80–350 GHz and B up to 15 T yield a magnetic anisotropy gap of the order of 60 GHz (2.9 K) and a g-factor of 2.2. In addition, the modelling reveals a positive single ion anisotropy (D>0) corresponding to an easy plane situation for the Ni₃ complex.     

Study of galvanomagnetic effects in Bi-Sr-Ca-Cu-O films

Galvanomagnetic effect has been studied at 77 K on Bi-Sr-Ca-Cu-O films as a function of d.c. bias current. These films were prepared by spray pyrolysis and screen-printing techniques, withT _c (R=0) 80 K and 100 K respectively. Magnetic field dependence ofI _c of sprayed-film showed very small hysteresis whereas screen-printed film showed greater hysteresis. Application of small magnetic field on these films destroyed the zero-resistance state and a finite resistance was developed. The slope of the resistance vs magnetic field curveΔR/ΔH depended on the current flowing through the sample. To increaseΔR/ΔH, meander-shape pattern was prepared on the sprayed film. In generalΔR/ΔH increased by a factor of 10³ after sample patterning. The possibility of using these films as a sensitive magnetic field sensor is discussed.     

High Field and Low Temperature Magnetization of ErCu2Si2 Single Crystal

The magnetic measurements have been performed for high fields up to 18 T and low temperatures down to 0.5 K on the single crystal compound ErCu₂Si₂. In the temperature dependence of magnetic susceptibility, two anomalies are seen at T _N =1.51 K and T _t =0.97 K which is corresponding to an antiferromagnetic ordering temperature and may come from a change of magnetic structure. Low temperature magnetization shows a metamagnetic transition around 0.4 T along the easy magnetization direction of [001]. The magnetization is almost saturated above 3 T and reaches 8.8μ _B /f.u. at 18 T. A metamagnetic transition appears around 0.5 T in the basal plane magnetization processes as well. The anisotropy within the basal plane is fairly large for high fields. These behaviors have been explained from crystalline electric field effects and magnetic interaction in terms of molecular field.     

Magnetic-field-induced non-linear effects of Josephson coupled superconductor Bi2Sr2CaCu2O8+δ

The dc current-voltage (I-V) relation along the c-axis of single crystalline Bi₂Sr₂CaCu₂O_8+δ has been measured in magnetic fields parallel and perpendicular to the c-axis. In zero field a clear and sharp jump with large hysteresis in theI-V curve was observed, indicative of the dc-Josephson effect. In magnetic field below a characteristic fieldB ^*≈0.4 T (at T=0 K) parallel to the c-axis the magnetic field suppresses the hysteresis and reduces the critical currentI _c drastically, whereas aboveB ^* theI-V curve becomes broad and featureless behavior. The characteristic field scaleB ^* can be interpreted as an energy scale of the Josephson coupling between superconducting layers in Bi₂Sr₂CaCu₂O_8+δ and is argued with emphasis on the correlation length of pancake vortices in this system.     

Magnetic Measurements on Single Crystal of Double Perovskite Ca2FeMoO6

We report the magnetism properties on single crystal of Ca₂FeMoO₆ double perovskite prepared by a floating zone technique. This high quality material has been studied by X-ray powder diffraction (XRD), and magnetic measurements. The field dependence of the magnetization at 5 K, 100 K, and 300 K suggest a ferrimagnetic behavior with a saturation magnetic moment of approximately 2.1 μ_B, 2.0 μ_B, and 1.4 μ_B per formula unit, respectively. From dc susceptibility, we observed two magnetic transitions at T _C1=380 K (paramagnetic–ferrimagnetic) and T _C1=336 K (orthorhombic–monoclinic phase).     

GMI磁传感器内部灵敏度与噪声特性研究

建立了非晶带GMI敏感元件的灵敏度和噪声理论模型,计算了其灵敏度和磁噪声在不同易轴方向和外磁场应用条件下的响应特性.通过改变易轴方向、外磁场及直流偏置场对非晶带敏感元件进行了优化,其内部磁噪声达到了fT/(√HZ)水平.分析了内部灵敏度、工作点和磁噪声水平对GMI磁传感器性能的影响,结果表明,在GMI磁传感器设计时,应...     

Coexistence of Low Damping and Strong Magnetoelastic Coupling in Epitaxial Spinel Ferrite Thin Films

Low‐loss magnetization dynamics and strong magnetoelastic coupling are generally mutually exclusive properties due to opposing dependencies on spin–orbit interactions. So far, the lack of low‐damping, magnetostrictive ferrite films has hindered the development of power‐efficient magnetoelectric and acoustic spintronic devices. Here, magnetically soft epitaxial spinel NiZnAl‐ferrite thin films with an unusually low Gilbert damping parameter (<3 × 10^?3), as well as strong magnetoelastic coupling evidenced by a giant strain‐induced anisotropy field (≈1 T) and a sizable magnetostriction coefficient (≈10 ppm), are reported. This exceptional combination of low intrinsic damping and substantial magnetostriction arises from the cation chemistry of NiZnAl‐ferrite. At the same time, the coherently strained film structure suppresses extrinsic damping, enables soft magnetic behavior, and generates large easy‐plane magnetoelastic anisotropy. These findings provide a foundation for a new class of low‐loss, magnetoelastic thin film materials that are promising for spin‐mechanical devices.