Modulating Magnetic Anisotropy And High-Frequency Properties Of Magnetic Thin Films Deposited On Pre-patterned Substrates

With the development of magnetic electronic devices towards thin film,high frequency and high speed,and low power consumption,modulating the magnetic anisotropy of magnetic thin films is a key problem in the development of integrated microwave magnetic devices,magnetic sensors and spintronics devices,etc.This dissertation focuses on the“Modulating magnetic anisotropy of magnetic thin films deposited on pre-patterned substrates”and a significant modulation of the magnetic anisotropy of films is achieved by depositing Ni₈₀Fe₂₀（Ni Fe）film on the sapphire substrate with nano-rippled patterns formed by annealing.This dissertation focuses on the preparation of nano-rippled pattern substrates,the optimization of substrate geometric parameters and the characterization and modulation of geometric correlation magnetic anisotropy of patterned magnetic films.In addition,the ferromagnetic resonance frequency,ferromagnetic resonance linewidth（damping）and the splitting phenomenon of FMR spectra for magnetic films on rippled substrates and other high-frequency properties are further studied.Finally,based on the fabricated rippled magnetic films,two types of magnetic devices,tunable broadband bandstop filter and planar Hall sensors,were designed,and a complete research chain of“process parameter-geometric parameter-magnetic anisotropy-application”was established.The main results of this dissertation are as followings:1.With the help of atomic force microscopy and transmission electron microscopy,in-depth research has been conducted on the rippled substrate formed by the thermal annealing process of m-plane sapphire,establishing the relationship between“process parameters-geometric parameters”,laying a foundation for subsequent research on magnetic anisotropy regulation and high-frequency characteristics.The study shows that changing the annealing time and temperature of the substrate can effectively modulate the morphology（wavelength and height）of the rippled sapphire substrate;The wavelength and height of substrate ripples are non-monotonically dependent on annealing time,and the height of ripples is positively correlated with annealing temperature.The morphology of the film sputtered on a rippled sapphire substrate is of a given dual ripple morphology.2.The in-plane uniaxial magnetic anisotropy of the Ni Fe film deposited on the rippled sapphire substrate was measured from multiple perspectives by Magneto-optical Kerr Effect tester,Ferromagnetic Resonance tester,Vibrating Sample Magnetometer and permeability spectra,and the corresponding relationship between the in-plane uniaxial magnetic anisotropy of the film and the rippled structure of the substrate was established.The magnetic field angle-dependent splitting phenomenon of ferromagnetic resonance spectra of magnetic films on rippled sapphire substrates was found.The mechanism was revealed to be related to the local ferromagnetic resonance caused by the inhomogeneous effective internal field of rippled films.3.The in-plane ferromagnetic resonance linewidths of magnetic films on rippled sapphire substrates were characterized in detail by the ferromagnetic resonance technique,and the angular correlation of ferromagnetic resonance linewidths of Ni Fe films on rippled sapphire substrates was fitted and analyzed.The linear width（damping）composition of the Ni Fe films on the rippled sapphire substrates was quantitatively separated,and the relationship between various magnetization relaxation mechanisms and the ripple morphology was revealed.4.The rippled sapphire substrate prepared under the optimal annealing conditions was used for oblique sputtering Ni Fe film,and more significant modulation of the magnetic anisotropy of films on rippled substrates has been achieved.It is found that the magnetic anisotropy of films oblique-sputtered on rippled substrates is related to the direction of the plane of material flux with respect to the ripple.When the plane of material flux is perpendicular to the direction of the ripple,the maximum uniaxial magnetic anisotropy field of Ni Fe film deposited on rippled substrate by the oblique-sputtering method is close to 1000 Oe,which is almost 3.3 times that of the normal-sputtered film on rippled substrate with the same substrate morphology,and 7.7 times that of the reference film deposited on plane sapphire substrate with the same oblique angle.The enhancement of magnetic anisotropy is related to the weakening of dipole interaction between ripple structures and the enhancement of shape magnetic anisotropy caused by microscopic columnar morphology.5.A tunable broadband bandstop filter was designed and fabricated based on Ni Fe film deposited on a rippled sapphire substrate.Due to the splitting phenomenon of the ferromagnetic resonance spectra of rippled films,the filter has a larger bandwidth compared to filter composed of film deposited on plane sapphire substrate.The characterization results show that even at a low external field（600 Oe）,the filter frequency linewidth is 310%larger than that of the filter with film on plane substrate.A planar Hall sensor based on Ni Fe film on a rippled sapphire substrate was designed and fabricated.The characterization results show that the sensitivity of the sensor is 45.2/Oe and the maximum measured magnetic field is 366 Oe.Due to the uniaxial magnetic anisotropy of the films on rippled substrates,this planar Hall sensor does not require additional patterning etching steps to induce uniaxial magnetic anisotropy,which simplifies the manufacturing process.