Study On Spin Pumping Effect In Ni₈₀Fe₂₀/Ru System

As the new era of 5G coming,the seventh information revolution put forward higher requirements for magnetic materials in information transmission and storage.Compared with the traditional magnetic devices,spin electronics devices bring a new revolution to the information revolution which have high speed,low operation energy and non-volatile properties.In this thesis,the spin pumping effect in Ni₈₀Fe₂₀/Ru system is studied by changing the thickness of ferromagnetic layer or nonmagnetic layer.Firstly,the efficiency of producing spin current and the spin mixing conductance in the system are calculated using experimental data.Secondly,the maximum spin diffusion distance is obtained by gradually changing the thickness of the nonmagnetic layer in this system.Finally,the relationship among spin pumping,acoustic mode resonance,and optical mode resonance in the Ni₈₀Fe₂₀/Ru/Ni₈₀Fe₂₀trilayer system is studied using the long-range dynamic exchange coupling model.The major contents are divided into three parts,shown as follows.1.In order to study the damping of spin pumping and the spin mixed conductance in Ni₈₀Fe₂₀/Ru system,the samples with highly consistent properties were prepared by using mask shielding method,which is used to prepare the samples as the intrinsic control group.The deviation of the intrinsic coefficients of single-layer samples was reduced from 3.1×10^-3 to 0.24×10^-3.It was found that the damping factor of Ni₈₀Fe₂₀ which thickness is 12 nm,14 nm,16 nm and 18 nm is between1.131×10^-3 and 1.505×10^-3.These results show that the spin pumping effect of our samples is strong,and that the measurement error is small.According to the spin pumping result obtained from ferromagnetic resonance method at the maximum spin diffusion distance and the saturation magnetization data measured by the vibrating sample magnetometer,the spin mixing conductance of the studied system was calculated,which is in the range of 8.55 nm^-2 and 10.41 nm^-2.The large spin mixing conductance than other reported similar systems can be attributed to the rough surface.2.In order to study the maximum diffusion distance of spin pumping effect in Ni₈₀Fe₂₀/Ru bilayer system,a wedge Ru film with a gradual increase of Ru thickness was fabricated by shutter shift technology,while the thickness of Ni₈₀Fe₂₀ film keeps the same.By this way,the intrinsic damping of Ni₈₀Fe₂₀ film is consistent everywhere,moreover,a series of samples with gradual increased Ru thickness can be obtained in one time.It should be mentioned that the samples exhibit a little uniaxial magnetic anisotropy due to the oblique angle between the target and substrate.However,the measurement error,caused by the magnetic anisotropy,can be ruled out as long as reasonably setting the relative orientation between the wedge-like film thickness and the magnetic anisotropy.The maximum diffusion distance of 8 nm in Ni₈₀Fe₂₀/Ru system was obtained by detecting the spin pumping effect in the samples with wedge-like Ru layer.It is interesting to note that an abnormal increase of damping constant was discovered in the thinner Ru region.The phenomenon was explained based on the spin back flow theory.3.The relationship between ferromagnetic resonance modes and spin pumping effect was investigated in Ni₈₀Fe₂₀/Ru/Ni₈₀Fe₂₀ trilayer system with various Ru thickness.With the increase of the thickness of Ru,the optical mode resonance frequency decays rapidly from 7.42 GHz to 3.13 GHz,while the acoustic mode fluctuates in a narrow frequency range of 1.01 GHz to 2.13 GHz.However,the damping of acoustic mode resonance is sensitive to the Ru thickness,while that of optical mode resonance is insensitive to the Ru thickness.This phenomenon is explained by the long-range dynamic exchange coupling theory,which is helpful for the study of high-frequency soft magnetic films.