Spin-Wave Studies In Patterned Magnetic Thin Films

Spin waves are the collective precession form of electron spins,which carry rich amplitude and phase information in the motion,and abandon the heat loss of traditional electron transport,thus becoming an ideal carrier for a new generation of low-energy storage devices.From GHz to THz,4 to 5 orders of magnitude smaller than microwaves of the same frequency,which makes them compatible with modern nanoscale electronic devices and circuits.With the miniaturization and high frequency of electronic devices,micro-and nano-scale electronic devices need to be prepared.Therefore,it is very important to study and manipulate the basic physical mechanism of micro-and nano-scale patterned thin film spin waves.In this paper,the patterning technique is used to study the resonance characteristics of soft magnetic thin films.The main contents are as follows:(1)First,patterns of different shapes were prepared on a single-layer Py film by photolithography,and its static and dynamic magnetic properties were studied.In the strip structure,different kinds of spin waves were excited and detected by means of detection methods such as CPW,ESR,PPMS,and BLS.The experimental results show that the in-plane rotation angle test is performed using CPW.When the applied field is parallel to the long axis of the strip and the microwave field is arranged perpendicular to the direction of the applied field,five different types of resonance modes are detected.The resonances at low frequencies are ferromagnetic resonance modes,and the resonances at high frequencies are in-plane spin standing wave modes of different orders.When the angle between the long axis of the strip and the direction of the applied field is changed,the number of in-plane spin standing waves gradually decreases with the increase of the angle,and there seems to be a certain coupling between the in-plane spin standing waves and the ferromagnetic resonance mode below a certain angle.When the applied field is perpendicular to the stripe direction,quantized spin-wave modes and consistent precession modes arising from the unsaturated region are detected.Out-of-plane rotation tests were performed with ESR,and multi-order vertical spin standing wave and forward bulk wave modes were observed.The wave numbers and peak intensities of the in-plane spin standing wave and perpendicular spin standing wave modes both satisfy the bulk inhomogeneity model.Using PPMS to conduct constant-frequency sweep field and low-temperature tests,it is observed that the in-plane spin standing wave moves to the lower field as the temperature decreases,while the perpendicular spin standing wave moves to the high field.This is because the in-plane direction is the easy axis direction,while the out-of-plane direction is the hard axis,and the magnetic moment precession is more inclined to the easy axis direction at low temperature.As the temperature decreases,the in-plane spin standing wave mode and the perpendicular spin standing wave mode gradually decrease,which is because there is a certain two-magnon scattering in the sample,and the consistent precessing ferromagnetic resonance during the two-magnon scattering process the mode(k=0)degenerates into a non-uniform precession mode(k≠0),and at low temperatures,the energy gap prevents the excitation of magnons below the gap energy.Using the BLS technique,the wave vector k=3.7 rad/μm was taken,and the surface wave and the backward body wave were excited and detected.Secondly,structures with different etching depths and disc sizes were prepared by photolithography and etching,and their static and dynamic magnetic properties were studied.The experimental results showed that the vortex structure disappeared when the etching was not complete,showing the same magnetic properties as continuous films.The perpendicular spin standing wave mode was detected by ESR excitation when the etch depth was 100 nm and the disk size was 10μm.Finally,nano-scale elliptical disks with different aspect ratios were prepared by electron beam exposure,and their related magnetic properties were studied.The results show that the change of the ratio of the major and minor axes of the elliptical disk has little effect on the spin wave modulus.(2)The static magnetic properties and dynamic magnetic properties of Py/Cu/Co and Py/Cu/Py trilayer film structures were firstly studied by VSM and VNA.By comparing the eigenfrequencies of the Py/Cu/Co trilayers,Py monolayers and Co monolayers,the resonant frequencies of the trilayers are between the resonant frequencies of the monolayers,indicating that optical branching and acoustic branching mode occurs in the trilayers.Using the CPW technique test,the results show that the trilayer film structure excites two resonance modes:the optical branch mode and the acoustic branch mode.With the increase of the thickness of the intermediate layer,the frequency of the optical branch mode gradually decreases.For ferromagnetic coupling,the interlayer coupling effect will increase the exchange coupling equivalent field effect,and the optical branch mode is derived from the interlayer coupling effect.The greater the thickness of the intermediate layer,the weaker the interlayer coupling,and the smaller the exchange coupling equivalent field effect,the lower the frequency of the optical branch mode.By comparing different upper layer materials,it is found that the onset frequencies of the optical branch modes are different,which is because the different saturation magnetizations of the upper layer materials lead to different interlayer coupling strengths.Secondly,a three-layer stripe structure was prepared by photolithography and etching,and the characteristics of angular resonance were studied by ESR.The results showed that the results of the trilayer film were similar to those of the single-layer film.The type and evolution of spin waves in the three-layer strip structure are very complicated because of boundary conditions and coupling effects.(3)Exploring the preparation of suitable coplanar waveguide electrodes to excite the spin wave conditions in permers provides an important basis for the subsequent use of coplanar waveguide electrodes to study spin waves in patterning.