| Surface Acoustic Wave（SAW）is a strain wave that propagates on the surface of a piezoelectric substrate,and it can be generated by applying RF electrical signals on the interdigital transducers（IDTs）made of metal fingers.Because the propagation velocity of SAWs is five orders of magnitude lower than that of electromagnetic waves,the wavelength excited at the same frequency is significantly shorter.Therefore,this strain wave component is more advantageous for miniaturization.With the miniaturization of devices,magnetic particles used for recording information have become difficult to flip with only an external magnetic field,while the frequencies of SAW devices can reach the GHz range（close to the ferromagnetic resonance frequency）.Since magnetic materials can interact with external stress,using the magnetoelastic properties of magnetic materials to manipulate magnetic moments has become an interesting way,where magnon-phonon coupling has received extensive attention.In this thesis,we mainly studied acoustically-driven magnetic resonance and non-reciprocal transmission of magnetoacoustic waves by varying the type and anisotropy of magnetic materials or the polarization state of SAWs.In addition,we also conducted some research on the phase transitions,static and dynamic magnetic properties,and magneto-acoustic control of magnetic thin films.The following is an abstract of the main research content of this work:（1）In Chapter 4,we first studied the definition,excitation and detection of SAW,as well as the signal characterization of SAW devices.Then,we systematically studied the influence of magnetic anisotropy on the magnetoacoustic resonance.In the experiment,we introduced magnetic anisotropy into magnetic materials using different methods.After analyzing the source of anisotropy,it was found that the origin of anisotropy in obliquely deposited Ni films is stress,the origin of anisotropy in patterned Ni films is shape anisotropy,the origin of anisotropy in an obliquely deposited Ni Fe film is shape anisotropy,and annealing can change the shape anisotropy of the grains in the obliquely deposited Ni Fe film.Based on this,we studied the influence of uniaxial magnetic anisotropy at different angles with SAW wavevector on the magnetic resonance spectrum.The results showed that the use of equivalent anisotropy fields can optimize the field configuration used in the experiment,and even directly excite magnetic resonance using SAW without external fields by setting the magnitude and direction reasonably.（2）In Chapter 5,we first studied the resonance coupling between SAWs transmitted along different crystal orientations on the Li Nb O3 substrate and Ni films.By comparing the magnetoacoustic resonance spectra of devices with and without the beam steering effect,different resonance results were found.Simultaneously observing SAW attenuation and non-reciprocity changes with quadrant in the devices with the beam steering effect.The theoretical model based on the LLG method described well the variation of SAW transmission with the external magnetic field and fitted the unique dynamic strain components in those devices with the beam steering effect.These SAW devices enrich the types of magnetoacoustic devices and have the potential for further optimization of performance.Secondly,the coexistence of acoustic transmission enhancement and attenuation caused by magnetoacoustic resonance is studied.Through SAW at 1048 MHz in Li Nb O3（Sub）/Co（10 nm）/Ni（10 nm）structure,a non-reciprocal device with an acoustic enhancement of more than 1.1 d B/mm is found.And it can be concluded that the acoustic enhancement is closely related to frequency and material properties.These results help to deepen the understanding of the physical mechanism of magnetoacoustic resonance and also contribute to the application of SAW devices in information processing,energy transmission,and other fields.（3）In Chapter 6,we do some research on the phenomenon of magnetically controlled acoustics.On the one hand,we studied the influence of different magnetization hysteresis processes in a Ni thin film on magnetoacoustic resonance and found that the magnetization state affects both the intensity and peak position of resonance absorption.On the other hand,to enhance the sensitivity of the magnetoelastic SAW device,we replaced the previous Ni thin film with a Ni Fe Ga thin film,and studied the preparation,static and dynamic magnetism of the film.Below the critical thickness,the Ni Fe Ga thin film exhibits better soft magnetic property than Ni,and stripe magnetic domain structure is observed in the Ni Fe Ga thin film above the critical thickness.On this basis,the magnetoacoustic resonance spectra were studied,and a low-damping acoustic-driven magnetic resonance is obtained in the Li Nb O3/Ni Fe Ga heterostructure. |
