Investigation Of Spin-pumping In Ferromagnetic/non-magnetic Film

Spintronics has always attracted lots of interests as an important research direction in the field of magnetics.The basic research material in Spintronics is nanoscaled magnetic film.The relaxation speed of the magnetic film material,in the dynamic motion of magnetic moment movement is determined by its magnetic dynamic damping factor,which plays a crucial role in the reading speed of magnetic storage and spintronic devices.Spin pumping is an efficient method to regulate the magnetic dynamic damping of a magnetic film without destroying its magnetic properties,which is an interfacial effect usually occuring in a magnetic heterostructure consists of a ferromagnetic film and a non-magnetic film?FM/NM?.By designing the properties of the NM layer and the FM/NM interface,the magnetic dynamic damping of the FM layer can be indirectly tuned.In this thesis,the rare earth metal and the transition metal are mainly used as the non-magnetic layer of the FM/NM system.The magnetodynamic damping factor of the films is changed with the thickness of the non-magnetic layer because of the spin pumping effect.Different insertion layers are used to study the influence of the interface between ferromagnetic and non-magnetic layers,and the regulation of spin pumping effect is realized.The main research results are as follows:1.In the Py/Cu_1-x-x Tb_x film system,when Tb is used as the non-magnetic layer,the Py/Tb film exhibits a significant in-plane uniaxial magnetic anisotropy,and the saturation magnetization of Py decreases with increased Tb thickness.The reverse magnetic moment of Tb in the atomic layer near Py/Tb can be induced by Py layer because of the magnetic proximity effect,forming an antiferromagnetic coupling at the interface.The magnetic dynamic damping factor of Py is obtained from the frequency dependence of the ferromagnetic resonance linewidth.The relationship between the magnetic dynamic damping factor and the thickness of the Tb consists well with the theoretical prediction of spin pumping.Results show that the strong spin-orbit coupling of Tb contributes to the enhancement of magnetic dynamic damping of Py.When Tb is doped into the Cu film,and the magnetic dynamic damping factor of adjacent Py is changed with the thickness of Cu-Tb layer and the concentration of Tb.Doping of Tb can effectively enhances the spin-orbit coupling of Cu film,which is conducive to improve the magnetic dynamic damping of Py.The spin-mixed conductance of the Py/Cu-Tb interface and the spin-diffusion length of the Cu-Tb layer can be obtained from the theoretical fitting of the results.It shows that the spin diffusion length of Cu decreases after Tb doping,which enhances the spin pumping effect.2.The Cu layer was inserted into the Py/RE bilayer interface,and Py/Cu/Tb and Py/Cu/Nd were compared.For the two series of films,when the Cu layer was inserted,the saturation field in the difficult axis direction became smaller.The saturation magnetization increases,indicating that the insertion of the Cu layer inhibits the induced magnetic properties of the interface.The interface of antiferromagnetic coupling is destroyed,which hinders the influence of the strong magnetocrystalline anisotropy of Tb on Py.According to the linewidth information of ferromagnetic resonance,the magnetization dynamic damping factor varies with the thickness of the Cu layer and the thickness of the Nd layer as well as the Tb layer.The results show that the value of magnetic dynamic damping factor tends to the value in bare Py film when the thickness of Cu is 4 nm.It is indicated that the Cu layer acts as an intercalation layer between Py/RE can destroy the antiferromagnetic coupling of the Py/RE interface and further affect the magnetodynamic damping factor of Py film.It also demonstrates that the antiferromagnetic coupling of the Py/RE interface can contribute to the enhancement of the magnetic dynamic damping of Py.3.Comparing rare earth and heavy metals as NM layers,in the Ta/Py/Cu/Pd/Ta series,when there is no Cu intercalated,Py/Pd,the saturation magnetization is the smallest.As the thickness of the Cu layer increases,the saturation magnetization increases,and the maximum value is 750 emu/cm³which is obtained when the thickness of the Cu layer is 10 nm.The coercive force is relatively small,and it remains at about 2 Oe.This is because magnetic moments of Pd atom antiparallel to Py are induced at the Py/Pd interface due to the magnetic proximity effect,and the induced magnetic moment can cancel the saturation magnetization of Py.When an intercalation layer of Cu is presented,the antiferromagnetic interface is weakened,thus the saturation magnetization is increased.According to the frequency dependency of the ferromagnetic resonance linewidth,we obtain the variation of the magnetic dynamic damping factor with the thickness of Pd and Cu.It shows that with the increase of the thickness of the insertion layer,and the magnetic damping factor of Py in Py/Cu/Pd system decreases first and then tends to be stable when the thickness of the insertion layer is larger than 4 nm.However,for different thicknesses of Pd,the stable magnetic dynamic damping factor still changes.In the Ta/Py/Pd/Nd/Ta series samples,when there is no Pd,it is Py/Nd,the saturation magnetization has the smallest value of 580 emu/cm³,as the thickness of the Pd layer increases,the saturation magnetization also increases,and the maximum value is about 728 emu/cm³ which is obtained when the thickness of the Pd layer is 10 nm.The coercive force is also maintained at about 2 Oe.It is shown that although the Py/Pd interface also constitutes antiferromagnetic coupling,the intensity is significantly weaker than the Py/Nd interface.According to the information of the magnetic resonance linewidth,the variation of the magnetization dynamic damping factor with the thickness of Nd and Pd is obtained.The magnetic dynamic damping of Py in Py/Pd/Nd system decreases with the increase of the thickness of the insertion layer,and also tends to a stable value when the thickness of the insertion layer is larger than 4 nm.However,for different thicknesses of Nd,the stabilized magnetic dynamic damping factor tends to the intrinsic damping factor of Py.