论文标题
垂直磁化ni $ _ {1-x} $ co $ _ {2+y} $ o $ $ _ {4-z} $外延薄膜的旋转和轨道磁矩
Spin and orbital magnetic moments in perpendicularly magnetized Ni$_{1-x}$Co$_{2+y}$O$_{4-z}$ epitaxial thin films: Effects of site-dependent cation valence states
论文作者
论文摘要
我们进行了X射线吸收光谱（XAS）和X射线磁圆二色性（XMCD）光谱，并研究了阳离子态状态和旋转和轨道磁矩在逆螺旋铁素铁的Ni $ _ {1- x} $ _ {1- x} $ _ {2+y} $ $ o $ $ o $ o $ $ o} $ o $ _ {4- {4- {4-垂直磁各向异性。我们表明，脉冲激光沉积在膜增长过程中的氧气压力p $ _ {O2} $不仅会影响阳离子化学计量（位点占领），还会影响阳离子价状态。我们的XAS结果表明，o $ _ {h} $ - 站点中的Ni位于+2至+3之间的中间价状态，Ni $^{（2 +δ） +} $（0 <$δ$ <1），其标称价值状态（$δ$值）在p $ _ {o2} $ {o2} $ {o2} $方面变化。另一方面，八面体（o $ _ {h} $）和四面体（t $ _ {d} $）站点的CO分别具有接近+3和+2的价状态。我们还发现，XMCD信号主要来自t $ _ {d} $ - 网站co $^{2+} $（co $ $ _ {td} $）和o $ _ {h} $ - site ni $^{（2+Δ） NCO电影。有趣的是，引起XMCD信号的Ni $^{（2+δ）+} $的价状态保持不变，独立于P $ _ {O2} $。负责磁矩和电导的Ni $^{（2+δ）+} $的电子结构与Ni $^{2+} $和Ni $^{3+} $的电子结构不同。此外，源自Co $ _ {td} $的轨道磁矩高达0.14 $μ__{b}/co_ {td} $，并平行于磁化，而ni $ _ {oh} $ orbital moment arbital moment Moment Moment Moment as Moment as as at Ni $ _ {b} 0.07 $μ__{b}/ni ni _ _ iS} $ 0.07 $ ______________}因此，Co $ _ {TD} $在膜的垂直磁各向异性中起关键作用。我们的结果证明了位点依赖性阳离子态对NCO膜的磁性和运输特性的重要性。
We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and investigated cation valence states and spin and orbital magnetic moments in the inverse-spinel ferrimagnet Ni$_{1-x}$Co$_{2+y}$O$_{4-z}$ (NCO) epitaxial films with the perpendicular magnetic anisotropy. We show that the oxygen pressure P$_{O2}$ during the film growth by pulsed laser deposition influences not only the cation stoichiometry (site-occupation) but also the cation valence state. Our XAS results show that the Ni in the O$_{h}$-site is in the intermediate valence state between +2 and +3, Ni$^{(2+δ)+}$ (0<$δ$<1), whose nominal valence state (the $δ$ value) varies depending on P$_{O2}$. On the other hand, the Co in the octahedral (O$_{h}$) and tetrahedral (T$_{d}$) sites respectively have the valence state close to +3 and +2. We also find that the XMCD signals originate mainly from the T$_{d}$-site Co$^{2+}$ (Co$_{Td}$) and O$_{h}$-site Ni$^{(2+δ)+}$ (Ni$_{Oh}$), indicating that these cation valence states are the key in determining the magnetic and transport properties of NCO films. Interestingly, the valence state of Ni$^{(2+δ)+}$ that gives rise to the XMCD signal remains unchanged independent of P$_{O2}$. The electronic structure of Ni$^{(2+δ)+}$ that is responsible for the magnetic moment and electrical conduction differs from those of Ni$^{2+}$ and Ni$^{3+}$. In addition, the orbital magnetic moment originating from Co$_{Td}$ is as large as 0.14 $μ_{B}/Co_{Td}$ and parallel to the magnetization while the Ni$_{Oh}$ orbital moment is as small as 0.07 $μ_{B}/Ni_{Oh}$ and is rather isotropic. The Co$_{Td}$ therefore plays the key role in the perpendicular magnetic anisotropy of the films. Our results demonstrate the significance of the site-dependent cations valence states for the magnetic and transport properties of NCO films.
