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1.
Magnetization and demagnetization behaviours of melt-spun Pr12Fe82B6 and Pr8Fe87B5 ribbons
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Nanocrystalline Pr_{12}Fe_{82}B_6 and nanocomposite Pr_8Fe_{87}B_5 ribbons have been prepared using a melt spinning technique. Recoil loops have been measured at 20, 200 and 300K. Demagnetization curves are analysed by dividing it into reversible and irreversible portions. High recoil loop susceptibility at low applied field and large reversible change in the demagnetization curve have been found in Pr_8Fe_{87}B_5 ribbons, showing that the reversible behaviours in nanocomposite permanent magnets originate primarily from the magnetically soft phase. The hysteresis in recoil loops found in Pr_8Fe_{87}B_5 ribbons originates from the soft phase α-Fe that suffers a stress. 相似文献
2.
研究了不同载荷作用下Tb0.3Dy0.7Fe2合金在压磁和磁弹性效应中磁畴偏转的滞回特性. 基于Stoner-Wolhfarth模型的能量极小原理, 采用绘制自由能-磁畴偏转角度关系曲线的求解方法, 研究了压磁和磁弹性效应中载荷作用下的磁畴角度偏转和磁化过程, 计算分析了不同载荷作用下磁畴偏转的滞回特性. 研究表明, 压磁和磁弹性效应中磁畴偏转均存在明显的滞回、跃迁效应, 其中磁化强度的滞回效应来源于磁畴偏转的角度跃迁; 压磁效应中预加磁场的施加将增大磁化强度的滞回, 同时使滞回曲线向大压应力方向偏移; 磁弹性效应中磁畴偏转的滞回存在两个临界磁场强度, 不同磁场强度下合金具有不同的磁畴偏转路径和磁化滞回曲线, 临界磁场强度的大小取决于预压应力的施加. 理论分析对类磁致伸缩材料磁畴偏转模型的完善和材料器件的设计应用非常有意义. 相似文献
3.
Jing PanYuan-chang Su Jing-guo Hu 《Journal of magnetism and magnetic materials》2012,324(8):1622-1626
The effect of noncollinearity between unidirectional and uniaxial anisotropies on asymmetric magnetization reversal of ferromagnet/antiferromagnet (FM/AFM) bilayer has been investigated. The results show the emergence of noncollinear anisotropies comes from the competition among applied magnetic field, magnetic anisotropy and exchange coupling in FM/AFM interface. The noncollinearity can lead to the asymmetry of hysteresis loop of FM/AFM bilayer. However, when the magnetic field is applied along the uniaxial anisotropy axis of FM layer, the hysteresis loop of FM/AFM bilayer is always symmetry independence of the noncollinear angle. Our results indicate that the asymmetry not only originates from the noncollinearity but also depends on the applied magnetic field orientation. Moreover, the asymmetry of hysteresis loop is always along with the appearance of unequivalence for magnetization reversal of FM/AFM bilayer, and there is a periodicity of π with orientation of applied field for its periodicity independence of the angle of the noncollinearity between the uniaxial and unidirectional anisotropies. The results can help us to open additional avenues to tailor the future advance magnetic device. 相似文献
4.
Using the principle of minimal energy and S-W model, the exchange bias for ferromagnetic/antiferromagnetic bilayers has been
investigated when the uniaxial anisotropy is misaligned with the exchange anisotropy. According to the relation between the
energy of the bilayer and the orientation of ferromagnetic magnetization, it is found that the bilayer will be in the monostable
state or bistable state when the external field is absent in the initial magnetization state. The monostable state or bistable
state of the bilayer, which determines the angular dependence of exchange bias directly, is controlled by the competition
between the exchange anisotropy and uniaxial anisotropy. When the applied field is parallel to the intrinsic easy axes and
intrinsic hard axes, one of the switching fields of the hysteresis loop shows an abrupt change, while the other keep continuous
by analyzing the magnetization reversal processes. Consequently, the exchange bias field and the coercivity will show a jump
phenomenon. The numerical calculations indicate that both the magnitude and direction of the exchange anisotropy will significantly
affect the angular dependence of exchange bias. The jump phenomenon of exchange bias is an intrinsic property of the bilayer,
which is dependent on the interfacial exchange-coupling constant, the orientation of the exchange anisotropy, the thickness
and uniaxial anisotropy constant of the ferromagnetic layer. 相似文献
5.
B. Fugiel 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):159-163
The parameters of the hysteresis loop in the ferroelectric Rochelle salt
were investigated using a sample with two pairs of electrodes: measurement
electrodes and the side ones. It has been shown that the difference between
the potentials of the measurement and the side electrodes (generating an
inhomogeneous electric field) leads to gradual decay in time t of the
remanent polarization Pr. The time required for the hysteresis loop to
disappear in the inhomogeneous electric field (not parallel to the
ferroelectric axis) decreases with temperature increase from 44±3 h
at – 9°C to 2.3±0.1 h at 21.9 °C. On the other hand, the
crystal placed for a sufficiently long time simultaneously in the measuring
electric field and in the constant inhomogeneous one may finally exhibit a
stationary hysteresis loop with a reduced remanent polarization and the
unchanged coercive field. It has been shown that the crystal as a whole does
not have to be polarized perpendicularly to the ferroelectric axis in order
for its hysteresis loop to be reduced. 相似文献
6.
采用能量极小原理及S-W模型研究了外应力对铁磁/反铁磁(FM/AFM)双层薄膜体系交换偏置的影响.不施加外磁场时,根据能量与铁磁层磁化强度方向之间的关系,指出体系存在单稳态和双稳态两种不同的状态,是由交换各向异性与单轴各向异性之间的竞争控制的.体系处于单稳态还是双稳态直接决定着交换偏置的角度依赖关系.分析磁化过程发现,外磁场沿内禀易轴及内禀难轴方向施加时,磁滞回线的一支转换场发生突变,而另一支转换场则保持不变,最终导致交换偏置场和矫顽场出现阶跃行为.数值计算表明,交换偏置场和矫顽场在阶跃点均具有较大的数值
关键词:
单稳态
双稳态
外应力 相似文献
7.
In this paper, we present the giant magneto-impedance (GMI) effect (real part of longitudinal impedance, Z, and of the off-diagonal impedance) and hysteretic magnetic properties of amorphous glass-coated microwires with different compositions possessing nearly zero, positive and negative magnetostriction constant and metallic nucleus diameter ranging between 6 and 16 μm. Enhanced soft magnetic properties (low coercivity of about 4 A/m) and high-GMI effect have been observed in Co-rich microwires with vanishing magnetostriction constant. The magnetic anisotropy field of these microwires depends on the ratio between metallic diameter, d and total microwires diameter, D. Stress-sensitive magnetic properties have been obtained in Fe-rich microwires after stress annealing: hysteresis loop stress-annealed (SA) microwires drastically changes under applied stress. A variety of hysteresis loops with different hysteresis loops can be obtained in Fe-rich microwires changing the conditions (time and/or temperature) of the stress annealing. The obtained results allow us to tailor the microwire magnetic properties for magnetic sensors applications through selection of their composition and/or geometry and by thermal treatment. 相似文献
8.
The decay of the hysteresis loop area of the system, which is obeying a site diluted kinetic Ising model, is considered by the disorder parameter using the effective field theory analysis. The exhibition focuses on the understanding of external field frequency, amplitude and the site concentration dependency of the hysteresis loop area for several powerful treatments. Important characteristics of the hysteretic response, such as frequency dispersion, effect of domain nucleation phenomenon on the dynamic process, etc., has been introduced together with well known other characteristics. An attempt has been made to explain the relations between the competing time scales (intrinsic microscopic relaxation time of the system and the time period of the external oscillatory field) and the shape of the response. As a result of the detailed investigations, existence of essentially three, particularly four types of dispersion curves have been propounded. 相似文献
9.
N. S. Kiselev I. E. Dragunov A. T. Onisan U. K. Rößler A. N. Bogdanov 《The European physical journal. Special topics》2008,158(1):119-124
The evolution of multivariant patterns in thin plates of magnetic shape memory materials with an applied magnetic field was
studied theoretically. A geometrical domain-model is considered composed of straight stripe-like martensite variants with
constant internal magnetization (high anisotropy limit) and magnetic domain wall orientation fixed by the twin boundaries.
Through integral transforms of the demagnetization energy, the micromagnetic energy is cast into a form convenient for direct
numerical evaluation and analytical calculations. The equilibrium geometrical parameters of multivariant patterns with straight
and oblique twin boundaries have been derived as functions of the applied field and the material parameters of a plate. It
is shown that the oblique multivariant states exist only in plates with thicknesses L larger than a certain critical value
L0. In samples with L<L0 a magnetic-field-driven transformation occurs directly between single variant states. 相似文献
10.
用自旋动力学方法系统地研究磁偶极相互作用表现的边界效应对小尺寸正方形铁磁薄膜的磁化翻转过程的影响.在确定的磁偶极相互作用强度下,针对不同的单轴各向异性强度和不同的磁化角(外磁场与易轴间的夹角),具体给出矫顽场与磁化角及单轴各向异性强度之间的依赖关系和-些有代表性的磁滞回线,并给出磁化翻转过程中-些有代表性的微观磁结构.模拟结果表明:磁偶极相互作用表现的边界钉扎作用与单轴各向异性场之间的竞争决定磁滞回线的形状和矫顽场的大小,从而在不同磁化角情况下会导致不同的矫顽场机理.本文提出可有效地描述正方形铁磁性薄膜复杂微观磁畴结构的形成与演变的五磁畴模型.这种五磁畴模型既能直接揭示单轴各向异性正方形铁磁薄膜的几何特性和物理特性,也方便于磁化翻转过程的分析. 相似文献
11.
L. I. Naumova M. A. Milyaev T. A. Chernyshova V. V. Proglyado I. Yu. Kamenskii V. V. Ustinov 《Physics of the Solid State》2014,56(6):1125-1130
A noncollinear configuration of magnetic anisotropy in spin valves with strong and weak interlayer couplings has been formed by annealing and cooling in a magnetic field. The dependence of the low-field magnetoresistance hysteresis loop width on the angle between the applied magnetic field and the principal axes of the magnetic anisotropy in a spin valve has been investigated. It has been found that, only in the case of a strong ferromagnetic interlayer coupling, the formation of a noncollinear configuration of the magnetic anisotropy provides a hysteresis-free character of the magnetization reversal of the free layer with retaining the maximum magnetoresistance and magnetoresistive sensitivity. 相似文献
12.
The hysteresis in Ni/Pb multilayers with layer thickness of 1.7, 5.5, 9.4 and 24.8 nm have been examined at low and room temperatures. The Stoner-Wohlfarth model, modified by the introduction of a constant internal field, well describes the shape of experimental hysteresis loops. The two components of internal field and anisotropy constant are fit to an individual loop. The transversal component of the internal field is related to a dispersion of local magnetization directions and determines a deviation of the rotation process from the Stoner-Wohlfarth model. At room temperature, the transversal component of the internal field for Ni/Pb multilayers is about 1000 Oe and is much greater than the effective anisotropy field and, as a result, the directions of magnetization rotate smoothly under the influence of resultant field. At low temperature, the longitudal component of the internal field is of the order of 1000 Oe and determines the incoherent rotations. 相似文献
13.
We observe a thermally induced spontaneous magnetization reversal of epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied magnetic field. Unlike any other magnetic system, the magnetization spontaneously reverses, aligning antiparallel to an applied field with decreasing temperature. We show that this unusual phenomenon is caused by the interfacial antiferromagnetic coupling overcoming the Zeeman energy of the ferromagnet. A significant temperature hysteresis exists, whose height and width can be tuned by the field applied during thermal cycling. The hysteresis originates from the intrinsic magnetic anisotropy in the system. The observation of this phenomenon leads to open questions in the general understanding of magnetic heterostructures. Moreover, this shows that in general heterogeneous nanostructured materials may exhibit unexpected phenomena absent in the bulk. 相似文献
14.
15.
A rigorous solution is given in the plane-wave approximation for the boundary problem of light reflection from the interface between an isotropic medium and a photorefractive crystal with drift-diffusion nonlinearity. The possibility of realizing hysteresis reflection or optical bistability in the system under certain conditions is shown. Analytical expressions are obtained that describe the hysteresis behavior of reflectivity as a function of the angle of incidence or the strength of a constant external electric field applied to the crystal. The results of the study are of interest for the development of devices controlling laser radiation. 相似文献
16.
Remanence curves have been measured of metal evaporated tape with a tilted easy magnetisation direction. A method to compensate for the demagnetising field was applied. The δm curve along the intrinsic easy direction shows combined positive and negative interactions, along the intrinsic hard direction only negative interactions. These results could be reproduced with a moving-Preisach Stoner-Wohlfarth hysteresis model. 相似文献
17.
N. V. Ershov V. A. Lukshina V. I. Fedorov N. V. Dmitrieva Yu. P. Chernenkov A. P. Potapov 《Physics of the Solid State》2013,55(3):508-519
The structural and magnetic states of ribbon samples of the soft magnetic alloy Fe-Si-Nb-B-Cu (6 at % Si) have been investigated after the nanocrystallization at a temperature of 550°C in a constant magnetic field (thermomagnetic treatment), in a field of mechanical tensile stresses (thermomechanical treatment), and without external effects. It has been shown that exposure to a constant magnetic field or a field of mechanical tensile stresses gives rise to a longitudinal anisotropy of magnetic properties. The mag- netic hysteresis loop transforms and becomes close to rectangular. This is accompanied by a significant increase in the residual magnetic induction, which approaches the saturation magnetic induction. While the time required to complete the processes of nanocrystallization is as short as 20 min and, under thermome- chanical treatment, the magnetic anisotropy is induced for 20 min, the time it takes to decrease significantly the coercive force of the alloys under thermomagnetic treatment is substantially longer (up to 60 min). After the thermomagnetic treatment, no lattice strains of α-FeSi nanocrystals have been found. Either they do not exist at all, or their values are within the error of the X-ray diffraction experiment. In the samples subjected to annealing under tensile loading, anisotropic lattice strains of nanocrystals with the values increasing pro- portionally to the applied stress have been revealed. The highest strains reaching 1% have been observed after the annealing under a stress of 860 MPa. 相似文献
18.
Lawrence Dresner 《Physica C: Superconductivity and its Applications》1998,310(1-4):213-217
At 77 K, the resistivity of ceramic, high-temperature superconductors grows gradually rather than sharply with increasing current. The critical-state theory of hysteresis losses therefore needs to be modified. This has been done for slab conductors whose resistivity can be taken proportional to a power of the current density. Simple formulas have been derived in the limiting cases of incomplete penetration and full penetration when the losses are driven either by a sinusoidal transport current or a sinusoidal external magnetic field. These formulas can be applied to multilayer transmission line cables once the current distribution within and among the layers has been determined. This distribution has been calculated (in the incomplete penetration limit) by solving Maxwell's field equations. A formula is presented for the dependence of the hysteresis loss on winding angle. The formula is used to determine the optimum winding angle. 相似文献
19.
Camarero J Sort J Hoffmann A García-Martín JM Dieny B Miranda R Nogués J 《Physical review letters》2005,95(5):057204
The magnetization reversal in exchange-biased ferromagnetic-antiferromagnetic (FM-AFM) bilayers is investigated. Different reversal pathways on each branch of the hysteresis loop, i.e., asymmetry, are obtained both experimentally and theoretically when the magnetic field is applied at certain angles from the anisotropy direction. The range of angles and the magnitude of this asymmetry are determined by the ratio between the FM anisotropy and the interfacial FM-AFM exchange anisotropy. The occurrence of asymmetry is linked with the appearance of irreversibility, i.e., finite coercivity, as well as with the maximum of exchange bias, increasing for larger anisotropy ratios. Our results indicate that asymmetric hysteresis loops are intrinsic to exchange-biased systems and the competition between anisotropies determines the asymmetric behavior of the magnetization reversal. 相似文献
20.
In the present work we use computational analysis based on the interacting hysteron model to address the question in how far intrinsic microscopic materials information can be retrieved from magnetic hysteresis loop data. Specifically, the goal is to understand whether it is possible to determine the intrinsic switching field distribution if exchange and magneto-static interactions of variable strength are simultaneously present in the material. We find that due to an existing degeneracy of hysteresis data sets, it is generally not possible to separately determine contributions from exchange and magneto-static interactions, even if the magnetization reversal is only partially correlated. However, the intrinsic switching field distribution could always be accurately determined, as long as the system remains in the uncorrelated or partially correlated magnetization reversal regime. 相似文献