The Interlayer Exchange Coupling And Optical Mode Resonance Enhancement In FeCo-based Sandwich Films With Magnetic Anisotropy

Radio-frequency and microwave devices based on ferromagnetic resonance(FMR)are widely used in the areas of communication,information,aerospace,military,etc.Higher and higher fr is in demand with the rapid development of technology.FMR frequency in soft magnetic films(SMFs)largely determines the maximum working frequency of magnetic devices.With the development of integrated circuit technology,high-frequency soft magnetic thin film materials without applied bias magnetic field(self-bias)become an urgently needed materials.In recent years,lots of research works have been carried out on self-biased high frequency SMFs materials for obtaining larger uniaxial magnetic anisotropy field,such as the using of oblique sputtering,composition gradient sputtering(CGS),ferromagnetic/antiferromagnetic interlayer coupling and magnetoelectric coupling etc.However,FMR frequency above 10 GHz is still difficult to obtain in self-biased SMFs.Recently,our research group found that in the ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM)sandwich films with strong interlayer exchange coupling,a pure optical-mode(OM)FMR with frequency up to 18 GHz was obtained by adjusting the relative orientation of the magnetic moment of ferromagnetic layers,which possess high magnetic permeability as well.The sandwich films are expected to become a kind of high-frequency soft magnetic material with practical value.Therefore,it has become an important research topic to study the mechanism of interlayer exchange coupling between FM/NM/FM multilayers and adjust the frequency and permeability of the optical-mode FMR.In this thesis,we investigated the formation and regulation mechanism of optical-mode FMR in FeCoB/Ru/FeCoB trilayers using different sample preparation method with different Ru thickness and researched the behavior of magnetoelectric coupling effect on magnetic properties in FeCoB/Ru/FeCoB/PMN-PT heterostructure.The main results were as follows:1.Different degrees of enhancement of ferromagnetic resonance were observed in both FeCoB/Ru/FeCoB(tRu=3.0 A)trilayers,which were prepared by oblique sputtering and component gradient sputtering method,respectively.The oblique sputtering trilayer show a well in-plane uniaxial anisotropy,and the anisotropy field increases greatly from 85 Oe to 417 Oe,while the corresponding resonance frequency was dramatically enhanced from 4.23 GHz to 8.36 GHz.Furthermore,the trilayer films also show a low damping of 0.012.In particular,an ultra-high frequency optical mode FMR was obtained from the trilayers prepared by component gradient sputtering.Due to strong antiferromagnetic coupling,the interlayer exchange coupling field JICE of the trilayers is up to 2534 Oe,with the OM resonance frequency fr0 enhance to 18.68 GHz and the initial permeability is maintained above 13,which reaches a practical level.It is also found that the FMR mode can switch nondestructively between ultra-high frequency optical mode resonance and low frequency acoustic mode resonance in a specific converted magnetic field,which provides a new possibility for the design of frequency-reconfigurable microwave devices.2.The effects of Ru thickness in FeCoB/Ru/FeCoB sandwich layers on the ferromagnetic coupling mode and resonance properties were investigated.We found that the coupling mode oscillates between ferromagnetic and antiferromagnetic as a function of Ru thickness,with rapidly decrement of coupling constant J.In the range of 2.1 A ?tRu ?15.0 A,both acoustic-and optical-mode resonance can be observed simultaneously.Particularly,in the biquadratic coupled trilayers with tRu=3.0 A,a pure OM resonance at zero bias field was found,possessing an ultrahigh resonance frequency of 19.55 GHz as J1 up to-4.41 erg/cm2 and maintaining considerable permeability.3.A FeCoB/Ru/FeCoB trilayer with pure optical-mode resonance was prepared on the(011)-cut PMN-PT single crystal substrates and the influence of magnetoelectric coupling stress on optical-mode resonance performance was investigated.The real easy axis direction of the OM trilayer films rotates anticlockwise with the increase of the bias electric field,through magnetoelectric coupling effect.The angle can be continually controlled by adjusting the electric field.The easy axis rotates 90 degrees exactly when the external electric field reaches 10 kV/cm and the microwave performances keep unchanged.The reciprocity of EA and HA is achieved,which provides a new entry point of OM resonance engineering.4.A series of superlattice multilayers as(FeCoB/Ru)n,[(FeCoB/Ru/FeCoB)/MgO]n and[(FeCoB/Ru/FeCoB)/ZnO]n were fabricated.The magnetic density was successfully increased in the[(FeCoB/Ru/FeCoB)/ZnO]n superlattice multilayers with a 250-nm effective ferromagnetic layer thickness.The multilayers exhibit good high-frequency performances with frO around 13.6 GHz and?i above 15.In particular,the switching of dual-mode ferromagnetic resonance under the control of the magnetic field was realized:high-frequency optical mode resonance around 13.6 GHz in low field(0-114 Oe)and low-frequency acoustic mode resonance about 4.5 GHz in the high field(>114 Oe).The superlattice structure provides a promising way to fabricate thick OM resonance films and provides greater freedom in designing and manufacturing multifunctional integrated circuit devices.