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arXiv · 2006.00777

Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates

A. Rastogi·Z. Li·A. V. Singh·S. Regmi·T. Peters·P. Bougiatioti·D. Carsten né Meier·J. B. Mohammadi·B. Khodadadi·T. Mewes·R. Mishra·J. Gazquez·A. Y. Borisevich·Z. Galazka·R. Uecker·G. Reiss·T. Kuschel·A. Gupta
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Abstract

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.

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A. Rastogi, Z. Li, A. V. Singh, S. Regmi, T. Peters, P. Bougiatioti, D. Carsten né Meier, J. B. Mohammadi, B. Khodadadi, T. Mewes, R. Mishra, J. Gazquez, A. Y. Borisevich, Z. Galazka, R. Uecker, G. Reiss, T. Kuschel, A. Gupta. 2020-06-01. Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates. https://doi.org/10.1103/physrevapplied.14.014014

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