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1.
何珂 《中国物理》2006,15(2):449-453
The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni0.8Fe0.2/Fe0.5Mn0.5 bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13.6 kA/4πms is high enough to bring about obvious changes in the hysteresis loops of the exchange bias bilayer. High sweep rate in the magnetization reversal stage enlarges the coercivity of the sample, while high sweep rate in the saturation state reduces the coercivity. The above phenomena were attributed to magnetic viscosity in the ferromagnetic layer enhanced by the interface exchange interaction and domain magnetization reversals assisted by thermal fluctuation in the antiferromagnetic layer respectively.  相似文献   

2.
Based on the Monte Carlo method, we simulate the magnetization curves with various magnetic field orientations for various single Co nanowires at room temperature. The simulated switching field as a function of angle between the field and the wire axis is consistent well with the experimental data. Correspondingly, the coercivity as a function of angle θ is presented, which together with the switching field plays an important role on explaining the magnetic reversal mechanism. It is found that the angular dependence of coercivity depends on the diameter of nanowires, and the coercivity and switching field versus θ deviate markedly from the prediction from the classical uniform rotation mode in the chain-of-sphere model. Furthermore, the magnetic reversal configurations display that magnetization reversal in the wires with small diameters is a nucleation-propagation process, and it is similar to the curling spread process in the larger wires.  相似文献   

3.
We synthesize the perovskite compound Sm Cr0.9Fe0.1O3 by the sol–gel method and investigate its exchange bias properties through thermomagnetic and isothermal magnetization measurements. The sign reversals of the exchange bias field are observed at the magnetization compensation temperatures 29.6 K and 96.2 K. It is demonstrated that the occurrence of the exchange bias originates from the antiferromagnetic coupling between the Cr-rich and Fe–Cr regions, of which the net magnetization is temperature-dependent. These results imply that there are potential applications in single systems with sign reversals of both magnetization and exchange bias.  相似文献   

4.
The training effect and the hysteresis behaviour of the angular dependence of exchange bias are extensively investigated upon the variation of the IrMn layer thickness tXrMn in a series of Co/IrMn bilayers. When tIrMn is very small, both of them are negligible. Then they increase very sharply with increasing tUMn and then reach maxima at almost the same value OftXrMn. Finally they both decrease when tIrMn is further increased. The similar variation trends suggest that these phenomena arise from irreversible change of antiferromagnet spin orientations, according to the thermal activation model.  相似文献   

5.
The influence of the interface exchange coupling on the magnetization reversal process for a FePt/α-Fe/FePt tri-layer structure has been studied through a micromagnetic approach.The analytical formula of the nucleation field has been derived.It is found that the nucleation field increases as the interface coupling constant rises.Especially when the thickness of the soft layer is small,the influence of the exchange coupling on the nucleation field is significant.The angular distributions of the magnetization for various exchange coupling constants have been obtained by numerical calculation.It is found that the angular distribution of the magnetization is discontinuous at the interface of the hard and soft layers.In the meantime,the pinning field decreases with the increase of the thickness of the soft layer and the exchange coupling constant.  相似文献   

6.
冯宏剑 《中国物理 B》2012,21(8):87103-087103
First-principals calculations show that magnetization reversal is accompanied by the opposite sense of rotation of the neighboring oxygen octahedra along the [1 1 1] direction which is called the antiferrodistortive displacement in BiCrO3. The coupling between magnetization and antiferrodistortive distortion is mainly caused by Dzyaloshinskii- Moriya interaction which is driven by the eg-eg states antiferromagnetic interaction in Cr-3d. A critical value of on-site Coulomb interaction prohibiting the Dzyaloshinskii-Moriya interaction and thus the magnetization reversal is found to be 1.3 eV.  相似文献   

7.
First-principals calculations show that magnetization reversal is accompanied by the opposite sense of rotation of the neighboring oxygen octahedra along the [1 1 1] direction which is called the antiferrodistortive displacement in BiCrO3.The coupling between magnetization and antiferrodistortive distortion is mainly caused by Dzyaloshinskii-Moriya interaction which is driven by the eg-eg states antiferromagnetic interaction in Cr-3d.A critical value of on-site Coulomb interaction prohibiting the Dzyaloshinskii-Moriya interaction and thus the magnetization reversal is found to be 1.3eV.  相似文献   

8.
The structure dependence of exchange bias in ferromagnetic/antiferromagnetic (FM/AF) bilayers has been investigated in detail by extending Slonczewski's 'proximity magnetism' idea. Here three important parameters are discussed for FM/AF bilayers, i.e. interracial bilinear exchange coupling J1, interracial biquadratic (spin-flop) exchange coupling J2 and antiferromagnetic layer thickness tAF. The results show that both the occurrence and the variety of the exchange bias strongly depend on the above parameters. More importantly, the small spin-flop exchange coupling may result in an exchange bias without the interracial bilinear exchange coupling. However, in general, the spin-flop exchange coupling cannot result in the exchange bias. The corresponding critical parameters in which the exchange bias will occur or approach saturation are also presented.  相似文献   

9.
Based on plasma kinetic theory, the instabilities of self-gravitation systems under perturbation with orbital angular momentum(OAM) are investigated, and the concept of twisted Jeans mode is introduced to describe the new phenomenon. The result shows that the growth rate of the Jeans instability is enhanced with the OAM parameter increased, while the critical wave number is consistent with the classical Jeans critical value. It is expected that the present results would give more insight into th...  相似文献   

10.
张开成  刘邦贵 《中国物理 B》2009,18(9):3960-3965
We have investigated the exchange bias and training effect in the ferromagnetic/antiferromagnetic(FM/AF) heterostructures using a unified Monte Carlo dynamical approach.The magnetization of the uncompensated AF layer is still open after the first field cycling is finished.Our simulated results show obvious shift of hysteresis loops(exchange bias) and cycling dependence of exchange bias(training effect) when the temperature is below 45 K.The exchange bias field decreases with decreasing cooling rate or increasing temperature and the number of the field cycling.Essentially,these two effects can be explained on the basis of the microscopical coexistence of both reversible and irreversible moment reversals of the AF domains.Our simulations are useful to understand the real magnetization dynamics of such magnetic heterostructures.  相似文献   

11.
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   

12.
白宇浩  云国宏  那日苏 《物理学报》2009,58(7):4962-4969
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   

13.
The angular dependence of the magnetization reversal in epitaxial Fe/IrMn bilayers with collinear and non-collinear cubic and unidirectional anisotropies is investigated. Multistep loops with different magnetization reversal processes are observed for either positive or negative angles with respect to the Fe easy axis. The angular dependence of the switching fields displays the broken symmetry of the induced non-collinearity. The experimental results are reproduced with a generalized domain wall nucleation model that includes the induced anisotropy configuration and the peculiar asymmetric magnetic switching behavior. These results highlight the importance of the relative angle between anisotropies in epitaxial exchange bias systems with incoherent rotation reversal mechanism, opening a new pathway for tailoring the magnetic properties of such systems.  相似文献   

14.
Experimentally an asymmetry of the reversal modes has been found in certain exchange bias systems. From a numerical investigation of the domain state model evidence is gained that this effect depends on the angle between the easy axis of the antiferromagnet and the applied magnetic field. Depending on this angle the ferromagnet reverses either symmetrically, e.g., by a coherent rotation on both sides of the loop, or the reversal is asymmetric with a nonuniform reversal mode for the ascending branch, which may even yield a zero perpendicular magnetization.  相似文献   

15.
徐东伟  高华  薛德胜 《物理学报》2007,56(12):7274-7279
依据实际的纳米线形貌,提出了描述磁性纳米线反磁化过程的截椭球链模型.基于此模型,推导了纳米线反磁化过程中不可逆磁化的临界场和矫顽力在一致转动和对称扇形模式下的表达式.同时,还研究了椭球间接触角、单轴磁晶各向异性、外场与链轴方向夹角、截椭球个数和椭球形状因子对临界场和矫顽力的影响.利用该模型解释了镍纳米线的反磁化过程可能是对称扇形的模式. 关键词: 截椭球链模型 反磁化 一致转动 对称扇形  相似文献   

16.
使用飞秒时间分辨抽运-探测磁光克尔光谱技术,研究了激光加热GdFeCo磁光薄膜跨越铁磁补偿温度时稀土-过渡金属(RE-TM)反铁磁交换耦合行为和超快磁化翻转动力学. 实验观察到由于跨越铁磁补偿温度、净磁矩携带者交换而引起的磁化翻转反常克尔磁滞回线以及在同向外磁场下,反常回线上大于和小于矫顽力部分的饱和磁化强度不同,显示出GdFeCo中RE与TM之间的非完全刚性反铁磁耦合. 在含有Al导热底层的GdFeCo薄膜上观测到饱和磁场下激光感应磁化态翻转及再恢复的完整超快动力学过程. 与剩磁态的激光感应超快退磁化过 关键词: 补偿温度 磁化翻转 反铁磁耦合 GdFeCo  相似文献   

17.
Submicron, circular, ferromagnetic-antiferromagnetic dots exhibit different magnetization reversal mechanisms depending on the direction of the magnetic applied field. Shifted, constricted hysteresis loops, typical for vortex formation, are observed for fields along the exchange bias direction. However, for fields applied close to perpendicular to the exchange bias direction, magnetization reversal occurs via coherent rotation. Magnetic force microscopy imaging together with micromagnetic simulations are used to further clarify the different magnetic switching behaviors.  相似文献   

18.
Magnetization reversal process and magnetoresistance (MR) hysteresis of single domain permalloy nanowires are numerically investigated by using OOMMF. It is shown that the abrupt jumps in the magnetoresistance are due to the domain formation and domain wall propagation so that a magnetic domain suddenly switches from one state into another. A nonmonotonic angular dependence of the jump (switching) field is found. Coherent rotation mode is responsible for the smooth variation of MR curves. The nucleation pattern of newly born domains depends on the tilted angle of external field.  相似文献   

19.
The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni80Fe20 antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni80Fe20 antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos θ| dependence. The angular dependence of out-of-plane coercivity of Ni80Fe20 antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane.  相似文献   

20.
A modified Monte Carlo Metropolis method is performed to simulate the hysteresis loops of a laterally oxidized Co nanopillar with an excised arc or an inclined circular plane. At low temperature after field cooling, an oscillatory exchange bias is observed with excised length or angle of inclination. However, the behaviors of coercivity exhibit a monotonous decrease with excision but an oscillation with tilt. The phenomena are intriguing and corroborated by means of the microscopic spin configurations and the magnetization reversal mechanisms. The occurrence of oscillatory exchange bias in such a Co/CoO composite nanopillar with direct exchange couplings is mainly because of the shape inducement in the nanopillar, which results in the energy fluctuations of interfacial coupling and the nonuniformity of domain distribution.  相似文献   

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