垂直各向异性Ho3Fe5O12薄膜的外延生长与其异质结构的自旋输运

垂直磁各向异性稀土-铁-石榴石纳米薄膜在自旋电子学中具有重要应用前景.本文使用溅射方法在(111)取向掺杂钇钪的钆镓石榴石(Gd_0.63Y_2.37Sc₂Ga₃O₁₂,GYSGG)单晶衬底上外延生长了2—100 nm厚的钬铁石榴石(Ho₃Fe₅O₁₂,HoIG)薄膜,并进一步在HoIG上沉积了3 nm Pt薄膜.测量了室温下HoIG的磁各向异性和HoIG/Pt异质结构的自旋相关输运性质.结果显示,厚度薄至2 nm的HoIG薄膜(小于2个单胞层)在室温仍具有铁磁性,且由于外延应变,2—60 nm厚HoIG薄膜都具有很强的垂直磁各向异性,有效垂直各向异性场最大达350 mT;异质结构样品表现出非常可观的反常霍尔效应和“自旋霍尔/各向异性”磁电阻效应,前者在HoIG厚度小于4 nm时开始缓慢下降,而后者当HoIG厚度小于7 nm时急剧减小,说明相较于反常霍尔效应,磁电阻效应对HoIG的体磁性相对更加敏感;此外,自旋相关热电压随HoIG厚度减薄在整个厚度范围以指数方式下降,说明遵从热激化磁振子运动规律的自旋塞贝克效应是其主要贡献者.本文结果表明HoIG纳米薄膜具有可调控的垂直磁各向异性,厚度大于4 nm的HoIG/Pt异质结构具有高效的自旋界面交换作用,是自旋电子学应用发展的一个重要候选材料.

Epitaxial growth of Ho3Fe5O12 films with perpendicular magnetic anisotropy and spin transport properties in Ho3Fe5O12/Pt heterostructures

Rare-earth iron garnet films with perpendicular magnetic anisotropy could open new perspectives for spintronics.Holmium iron garnet(Ho₃Fe₅O₁₂,HoIG)films with thickness ranging from 2 to 100 nm are epitaxially grown on(111)orientated gadolinium gallium garnet single crystal substrate doped with yttrium and scandium(Gd_0.63Y_2.37Sc₂Ga₃O₁₂,GYSGG)by ultra-high vacuum magnetron sputtering.A 3-nm Pt film is further deposited on each of the HoIG films.The magnetic anisotropy and magneto-transport properties of heterostructures at room temperature are investigated.It is shown that the HoIG film as thin as 2 nm(less than two unit cells in thickness)exhibits the ferromagnetic properties at room temperature,and perpendicular magnetic anisotropy is achieved in the 2-60 nm thick films,and a maximum effective perpendicular anisotropy field reaches 350 mT due to the strain induced magnetoelastic anisotropy.The HoIG/Pt heterostructure shows significant anomalous Hall effect(AHE)and appreciable spin-Hall magnetoresistance(SMR)and/or anisotropic magnetoresistance(AMR).Remarkably,the AHE starts to decline gradually when the HoIG thickness is less than 4 nm,but the magnetoresistance decreases rapidly with the HoIG layer becoming less than 7 nm in thickness.The fact that the AHE in the heterostructure is less sensitive to the HoIG thickness suggests that the interface effect is more dominant in the AHE mechanism,whereas the bulk magnetic properties of the HoIG plays a more important role for the observed magnetoresistance.In addition,the spin Seebeck effect decreases exponentially with the decrease of HoIG thickness till the ultrathin limit,which was previously validated in the micrometer-thick YIG/Pt stacks in the frame of thermally excited magnon accumulation and propagation.The present results show that the nanometer HoIG/Pt heterostructure with tunable perpendicular magnetic anisotropy and efficient interfacial spin exchange interaction could be a promising candidate for insulating magnet based spintronic devices.