Effect Of Strain On Magnetic And Transport Behaviors In Metamagnetic FeRh Thin Films

In recent years,the emergence of wearable device has led to the rapid development of flexible magnetic electronics.The development of flexible magnetic electronics needs to break through two problems: how to realize the flexibility of magnetic electronic materials and devices,how to control its physical property under different strain.In this thesis,we focus on the second problem to study the strain effect on the magnetic,antiferromagnetic and metamagnetic transition of FeRh thin film.First,we studied the epitaxial growth of FeRh films on different single crystals and the influence of epitaxial strain on the metamagnetic transition between AFM and FM phases.For FeRh films on STO and MgO substrates,the epitaxial growth shows a 45° in-plane structure rotation relationship.In contrast,FeRh on LAO displays a mixed epitaxial growth of both 45° in-plane structure rotation and cube-on-cube relationship.The critical temperature for the magnetic phase transition of FeRh can be changed between 405 and 360 K due to the different growth strains.Upon applying a magnetic field,these critical temperatures decrease at a rate of-8.5,-7.1 and-9.7 K/T for FeRh films grown on MgO,STO and LAO,respectively.The MR reaches a maximum value at 380,340,and 320 K for FeRh films grown on STO,MgO and LAO substrates,respectively.Secondly,we studied the mechanical strain effect on the flexible FeRh/PDMS thin film.The as-prepared samples have wrinkle structure,and then it can bear more bending stress/strain compared to flat films.It was found that the mechanical strain has no effect on the magenrtic properties in our wrinkled FeRh/PDMS thin film,and the metamagnetic transition temperature have no change.However,our investigations of the transport properties under different strain suggest that there are micro-cracks in the film.We have built up a model to investigate the effect of micro-cracks on the transport properties of FeRh film.Thirdly,we studied the electric field control of magnetic transition in FeRh/PMN-PT heterostructure.The as-prepared samples present a first-order transition from AFM to FM orders at a transition temperature around 360 K.It was found that the transition temperature typically shift down by ~ 15 K with 1 kV/cm electric field applied through PMN-PT substrate at 360 K.This kind of behavior is corresponding to that of isothermally convert of the FeRh from FM-dominated to AFM and FM consistent state.Moreover,stable and remarkable high/low magnetization states can be achieved by sweeping the positive and negative electric field.In addition,the relatively symmetric dependence of the magnetization on the electric field indicates that this giant magnetoelectric response is mainly driven by voltage-induced strain.Finally,we grew CoFeB thin film on the top of epitaxial FeRh films.There is exchange coupling eefect between CoFeB and FeRh films.When measuring the magnetic properties of CoFeB films,it was found that the magnetic anisotropy of CoFeB films can be affected by the magnetic anisotropy of FeRh films.Then we grew CoFeB/ FeRh films on PMN-PT substrate to study the strain effect on the antiferromagnetic of FeRh films at room temperature.We found that FeRh films are not epitaxially grown on PMN-PT substrate,so now the study is still in progress.