Temperature Dependence of the Spin Seebeck Effect in a Mixed Valent Manganite

We report on temperature dependent measurements of the longitudinal spin Seebeck effect (LSSE) in the mixed valent manganite ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$. By disentangling the contribution arising due to the anisotropic Nernst effect, we observe that in the low temperature regime, the LSSE exhibits a $T^{0.5}$ dependence, which matches well with that predicted by the magnon-driven spin current model. Across the double exchange driven paramagnetic-ferromagnetic transition, the LSSE exponent is significantly higher than the magnetization one, and also depends on the thickness of the spin-to-charge conversion layer. These observations highlight the importance of individually ascertaining the temperature evolution of different mechanisms—especially the spin mixing conductance—which contribute to the measured spin Seebeck signal.

Figure 1

(a) and (b) Schematic illustrations of the device for measuring the ANE and the total signal ($\mathrm{LSSE}+\mathrm{ANE}$), respectively. (c) and (d) The $H$ and $\nabla T$ dependence of these signals with a 10 nm Pt and a 13 nm W overlayer. The linearity as a function of $\nabla T$ and the reversal of the sign of the LSSE between the Pt and W layers confirms the intrinsic nature of the measured spin Seebeck signal.

Figure 2

(a) The temperature dependence of the magnetization and the resistivity of the bare LCMO film. (b) and (c) The temperature dependence of the total, ANE and LSSE signals as measured on devices with Pt thickness of 5 and 10 nm, respectively.

Figure 3

The temperature dependence of $V_{\mathrm{LSSE}}$ at temperatures below 60 K. In the region where $\mathrm{\Delta }{T}_{\mathrm{eff}}$ remains invariant, the LSSE signal varies as $0.47\pm 0.01$ and $0.53\pm 0.02$ in LAO/LCMO/Pt devices with Pt thickness of 10 and 5 nm, respectively.

Figure 4

The $T_C-T$ dependence of the magnetization and the LSSE signals are depicted in (a) and (b), respectively. The critical exponent of $V_{\mathrm{LSSE}}$ is seen to be much larger than that of the magnetization, and also varies with the thickness of the Pt spin-to-charge conversion layer.