The Study Of Magnetic Anisotropy Of FeRh Thin Films And Related Heterostructure

The B2-type ordered binary FeRh alloy will transform from antiferromagnetic(AFM)state to ferromagnetic(FM)state as temperature rises in a certain range near room temperature,that is,the first-order phase transition of FeRh.This phase transition and related accompanying properties make it increasingly widely used in spintronic devices,so the study of the basic magnetic properties of FeRh alloy is particularly important.Among them,magnetic anisotropy is an important parameter when FeRh alloy is applied to devices in thin film form,and it is also the key property of this paper.In this work,epitaxial FeRh thin films and a CoFeB/FeRh heterostructure were grown by using magnetron sputtering system,respectively.In this paper,focusing on magnetic anisotropy,the magnetic properties of epitaxial FeRh films on different substrates and related heterostructure under exchange coupling were studied.First,we epitaxially grown epitaxial FeRh films on different(001)oriented single crystal substrates,including Sr Ti O₃(STO),Mg O,and La Al O₃(LAO).The changes of magnetic anisotropy and magnetic damping of FeRh thin films subjected to different epitaxial strain were studied.The results show that the epitaxial relationship of FeRh films on STO or Mg O substrate is FeRh[100](001)//substrate[110](001)while for LAO substrate is FeRh[100](001)//LAO[100](001).The films are subjected to in-plane compressive strain when grown on the former two substrates and to tensile strain on LAO substrate.FeRh thin films exhibit superposition of an in-plane fourfold anisotropy and an extra uniaxial anisotropy on all kinds of substrates and the easy axes of the fourfold anisotropy are along the FeRh <100>directions at FM state.The remanent magnetization in AFM state,phase transition temperature,magnetic anisotropy,and magnetic damping of FeRh films under different epitaxial strains display significant differences,indicating that the magnetic properties of FeRh film are very sensitive to epitaxial strain.Secondly,we fabricated amorphous CoFeB/epitaxial FeRh bilayer on STO(001)substrate and carried out studies of related magnetic properties.The results show that,as FeRh film transfers from AFM to FM state,the heterostructure changes from FM/AFM to the FM/FM system.The magnetic anisotropy of FeRh film can be imprinted to the CoFeB layer through the exchange bias coupling and exchange spring coupling during the phase transition,respectively.It can be known that the FeRh/STO film has an in-plane fourfold anisotropy along FeRh<100>directions in AFM state.In addition,the exchange coupling effect in heterostructure is also reflected in the change of the magnetic damping parameter during the phase transition.