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Study the epitaxial Fe thin films on MgO substrate have attracted much attention in recent years,which is because of Fe/MgO/Fe structure having a very high tunneling magnetoresistance [1].The magnetic switching process is crucial when using such Fe films for spintronic applications.For(001)films,magnetocrystalline anisotropy have two hard axes.When the magnetic moment crosses “hard” axis in the plane and needs to overcome the domain pinning energy [2].So,these(001)films magnetic switching processes can be understood by the domain pinning energy and magnetic anisotropy constants.Angular dependence of anisotropic magnetoresistance(AMR)with different external magnetic fields was measured to investigate magnetic anisotropy and reversal process of Fe/MgO(001)system.The direction of current was designed to deviate a certain angle(α= 6.3°)from hard axis in resistance measurement.One reason is that two orientations of magnetization along the two easy axes can be distinguished by magnetoresistance,the other one is that the designed deviated angle can detect slight change of magnetization induced by coherence rotation.This makes high sensitive to investigate the reversal process.When the investigation was performed with external fields higher than saturation field,the magnetization process is basis on coherent magnetization reversal(Stoner-Wohlfarth-like).The magnitudes and orientations of various magnetic anisotropy constants,including intrinsic four-fold(K1)and uniaxial magnetic anisotropy(KU),derived from AMR curves,can be used to described this process.In low fields,nucleation of magnetic domains and rapid displacements 90° domain walls are dominated in the magnetic switching process,which is shown an abrupt transition between its maximum and minimum of low field AMR.Moreover,AMR measured in intermediate field has tilted plateau can be well interpreted by domains pinning and coherent magnetization discussed above.