High Frequency Dynamics Of Multilayer With Interface Exchange Coupling

Exchange interaction is widely found within magnetic materials and interface between different materials.Rotatable anisotropy,optical ferromagnetic resonance,giant magnetism resistance and exchange bias effect caused by interface exchange coupling provide a new way for the study of thin film materials.It has become a research hotspot to discover the new properties of interface exchange coupling and regulate high frequency magnetic properties of multilayers.This thesis focuses on the research of rotatable anisotropy,optical ferromagnetic resonance,and magnetic properties at low temperature based on the interface exchange coupled ferromagnetic multilayers.The main results are as follows:1.Unbiased rotatable anisotropy has achieved in Fe₂₀Ni₈₀/FeMn bilayer.In-plane omnidirectional permeability of the bilayer was detected by regulating interface exchange coupling.In experiment,we successfully stripping the rotatable anisotropy from ferro-antiferromagnetic exchange coupled bilayer,and verified the theory of Stiles et.al about the exchange bias systems that the exchange bias effect and the rotatable anisotropy originate from reversible and irreversible rotation of antiferromagnetic grains,respectively.2.The interface exchange coupling field of Fe₂₀Ni₈₀/Co bilayer was found to be inversely proportional to square of the layer thickness.Compared with the variation of acoustic mode,the optical resonance frequency decreases with the increase of Fe₂₀Ni₈₀layer thickness,which is mainly caused by the decrease of interface exchange coupling.By fitting f-H curve of acoustic and optical resonance,it was found that the variation of coupling field with layer thickness satisfy₀)^?2,where exchange constant=0.57×10^-6erg?cm.The interface exchange coupling can be regulated by doping Zirconium in Co layer,and thus the optical resonance frequency can be changed.3.We found that optical permeability of Fe₂₀Ni₈₀/Co bilayer increases with the increase of external magnetic field.We proposed a theoretical model for dynamical response of the magnetization of interface exchange coupled magnetic bilayer.The expressions for dispersive relation and permeability of the bilayer were derived.Combining with experimental results,we proved that the increase of optical permeability is originated from out-of-phase precession of the two layers'magnetic moments.The calculations based on the theoretical model show that the optical permeability increases firstly with the increase of external field and then decreases as the field continues to increase.The critical field where the permeability reaches extreme value is closely related to layer thickness and the directions of external field.4.In Fe₂₀Ni₈₀/Co bilayer,the relation between the exchange intensity_inter and temperaturegives<1.The variable frequency sweeping field ferromagnetic resonance at different temperature was obtained via PPMS measurements,proving that_inter??andsatisfy_inter??/_inter?0??1-.The fitting parameter=0.59,is much less than the value of 1.5 given by references.Such a difference might result from discrepancy between saturation magnetizations of the ferromagnetic layer.