Enhancement in Thermally Generated Spin Voltage at the Interfaces between Pd and NiFe2O4 Films Grown on Lattice-Matched Substrates
Enhancement in Thermally Generated Spin Voltage at the Interfaces between Pd and NiFe2O4 Films Grown on Lattice-Matched Substrates
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DOI：
10.1103/physrevapplied.14.014014
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发表时间：
2020-06
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通讯作者：
A. Rastogi;Z. Li;Anuradha Singh;S. Regmi;T. Peters;P. Bougiatioti;D. Carsten né Meier;J. Mohammadi;B. Khodadadi;T. Mewes;R. Mishra;J. Gázquez;A. Borisevich;Z. Galazka;R. Uecker;G. Reiss;T. Kuschel;A. Gupta
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作者：
A. Rastogi;Z. Li;Anuradha Singh;S. Regmi;T. Peters;P. Bougiatioti;D. Carsten né Meier;J. Mohammadi;B. Khodadadi;T. Mewes;R. Mishra;J. Gázquez;A. Borisevich;Z. Galazka;R. Uecker;G. Reiss;T. Kuschel;A. Gupta
通过纵向几何形状的自旋塞贝克效应测量，证明了从外延亚铁磁 NiFe$_2$O$_4$ 薄膜到 Pd 层的有效自旋注入。 NiFe$_2$O$_4$ 薄膜（60 nm 至 1 $\mu$m）通过脉冲激光沉积在同结构尖晶石 MgAl$_2$O$_4$、MgGa$_2$O$_4$ 和 CoGa$_2$O$_4$ 基板上生长，晶格失配在 3.2% 至 0.2% 之间变化。对于较薄的薄膜（$\leq$ 330 nm），随着晶格失配的减少，观察到自旋塞贝克电压的增加，这与铁磁共振测量确定的吉尔伯特阻尼参数的减少密切相关。高分辨率透射电子显微镜研究表明，随着晶格失配的减少，导致薄膜中应变弛豫（即失配位错）的反相边界和界面缺陷显着减少。这凸显了减少尖晶石铁氧体结构缺陷对于高效自旋注入的重要性。进一步表明，角度相关的自旋塞贝克效应测量提供了一种定性方法来探测薄膜中存在的面内磁各向异性。
Efficient spin injection from epitaxial ferrimagnetic NiFe$_2$O$_4$ thin films into a Pd layer is demonstrated via spin Seebeck effect measurements in the longitudinal geometry. The NiFe$_2$O$_4$ films (60 nm to 1 $\mu$m) are grown by pulsed laser deposition on isostructural spinel MgAl$_2$O$_4$, MgGa$_2$O$_4$, and CoGa$_2$O$_4$ substrates with lattice mismatch varying between 3.2% and 0.2%. For the thinner films ($\leq$ 330 nm), an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch, which correlates well with a decrease in the Gilbert damping parameter as determined from ferromagnetic resonance measurements. High resolution transmission electron microscopy studies indicate substantial decrease of antiphase boundary and interface defects that cause strain-relaxation, i.e., misfit dislocations, in the films with decreasing lattice mismatch. This highlights the importance of reducing structural defects in spinel ferrites for efficient spin injection. It is further shown that angle-dependent spin Seebeck effect measurements provide a qualitative method to probe for in-plane magnetic anisotropies present in the films.