Investigation Of Spin-pumping In Ferromagnetic/Rare Earth Bilayer Film

The study of magnetic thin films has always been a hot issue in the field of magnetics.Ferromagnetic films especially permalloy?NiFe,Py?with excellent soft magnetic performances such as high saturation magnetization and low coercive force have received tremendous attention in spintronics.Recently,spin pumping was discovered in a magnetically heterostructure with a ferromagnetic/nonmagnetic?FM/NM?interface,which can be utilize to modulate the magnetodynamic damping in FM layer and the effect was different for various NM materials.A large number of experiments indicate that heavy metals with large spin-orbit interactions such as Pt and Pd can arouse a huge spin pumping effect,thus they are considered to be excellent non-magnetic metal candidates in the FM/NM system.However,studies attempting to examine rare earth?RE?as a component of the NM layer are relatively few.Motivated by these considerations,we tried to investigate the spin pumping effect and the modulation of magnetodynamic damping in FM/RE and FM/RE-Cu systems.Nd is a light rare earth metal with a magnetic transition temperature of 7.5 K and a paramagnetic transition temperature of 19 K.It exhibits paramagnetism at temperatures above 20 K and its electrical conductivity comes from 4f electrons.Due to the influence of the crystal field is tiny,the spin-orbit coupling in Nd film is relatively large.Ho is a heavy rare earth metal that exhibits paramagnetism at temperatures above 20 K,has a larger atomic magnetic moment than Nd,and also has strong spin-orbit coupling.Cu is a non-magnetic metal with 3d itinerant electrons,and its spin-orbit coupling is weak,so the spin pumping effect in Py/Cu is almost invisible.In this dissertation,both light and heavy RE were respectively used as the NM layer in FM/NM systems.The modulation effect of the magnetodynamic damping factor and the spin pumping effect of the Py/Nd and Py/Ho double-layer films along with the spin-orbit coupling of the rare earth nonmagnetic layer were studied by changing the thickness of the NM layer.Furthermore,the spin-orbit coupling of the NM layer is manipulated by Cu dopping in RE films.The main results are as follows:1.For Py/Nd_1-xCu_x series samples,when the Py thin film was adjacent by rare earth Nd,a uniaxial in-plane magnetic anisotropy with anisotropy field of about 18 Oe was observed;and saturation magnetization of Py decreased from 860 emu/cm³ to 630 emu/cm³,indicating that the antiparallel magnetic moment are induced in Nd because of the magnetic proximity effect in Py/Nd interface,which cancels the saturation magnetization of part of Py.While doping with Cu in Nd,the in-plane uniaxial anisotropy decreases with the increase of Cu content,implying that the amorphous Nd-Cu layer coverage may inhibit the magnetic anisotropy of the Py/Nd-Cu film;the saturation magnetization of the Py layer displays an increase tendency,suggesting that Cu doping may weaken the magnetic proximity effect between the Py layer and the Nd-Cu layer.For the Py/Ho_1-xCu_x sample,there is also a magnetic proximity effect at the interface,and the variatrion trend of the saturation magnetization of Py is basically the same as in Py/Nd_1-x-x Cu_x;however,its magnetic proximity effect at the interface is weaker than that of Nd,and the effect of doping Cu on the neighboring effect is also weaker than that of Nd;2.For both Py/Nd-Cu and Py/Ho-Cu,the ferromagnetic resonance linewidth increase linely with the frequency,and the non-uniform widening is very low,which indicates that the double-scattering in our sample is negligible.By fitting the frequency dependence of ferromagnetic resonance linewidth,the variation of the effective magnetization and magnetization damping factor with the thickness of non-magnetic layer Nd?Ho?-Cu and the concentration of Cu was obtained.Results show that the growth of the magnetization dynamic damping factor of Py/Nd?Ho?-Cu satisfies the trend of the spin pump.When the thickness of the non-magnetic layer is thin,the Nd-based non-magnetic layer contributes less to the Py magnetization dynamic damping factor than the Ho-based non-magnetic layer;when the thickness of the non-magnetic layer is relatively thick,the Nd-based non-magnetic layer contributes more to the Py magnetization dynamic damping factor than the Ho-based non-magnetic layer.With the increase of Cu content,the damping factor of magnetization dynamics decreases for both Py/Nd-Cu and Py/Ho-Cu,which indicates that the incorporation of Cu weakens the spin-orbit coupling of the non-magnetic layer;3.By theoretical caculation,the spin-mixing conductance at the equivalent interface of the Py/Nd?Ho?-Cu thin film and the spin diffusion length of the Nd?Ho?-Cu layer were obtained.Results show that the spin diffusion length in Nd?11.6 nm?is similar to Ho?10.9nm?;with the increase of Cu content,spin diffusion length in RE increases significantly,and the effective spin-mixing conductance decreases obviously,which further confirms that Cu incorporation weakens the spin-orbit coupling of the non-magnetic layer and modulates the spin pumping effect.