外应力对铁磁/反铁磁体系交换偏置的影响及阶跃现象

Effect of applied stress on exchange bias in ferromagnetic/antiferromagnetic bilayers and the phenomenon of the jump

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.外应力的大小及方向对交换偏置均有很大的影响,均可以使体系在单稳态与双稳态之间转变,导致角度依赖关系发生显著变化.研究表明,外应力可作为一种可行的方法来控制和调节FM/AFM体系的交换偏置.

Using the principle of minimal energy and S - W model, the effect of the applied stress on exchange bias in ferromagnetic （FM） / antiferromagnetic （AFM） bilayers has been investigated. When the applied field is absent, according to the relation between the energy of the system and the orientation of ferromagnetic magnetization, the system will be in monostable state or bistable state, which is controlled by the competition between the uniaxial anisotropy and the exchange anisotropy. Monostable state or bistable state of the system determine the angular dependence of exchange bias immediately. When the extemal field is applied along the intrinsic easy axes and intrinsic hard axes, it is found by analyzing the magnetization processes that one of the switching field of the hysteresis loop shows a an abrupt change, while the other is kept constant, and consequently the exchange bias field and the coercivity will appear a jump phenomenon. The numerical calculations indicate that both the exchange bias field and the coercivity are larger in the magnitude at the points of the jump. Both the magnitude and the orientation of the applied stress will significantly affect the exchange bias by making a transition between monostable state and bistable state in the system. This transition induces a significant change in angular dependence of the exchange bias. Our results demonstrate that the applied stress is a viable way to control and tune the exchange bias of the FM/AFM bilayers.