Temperature dependence of current polarization in Ni$_{80}$Fe$_{20}$ by spin wave Doppler measurements*

The temperature dependence of current polarization in ferromagnetic metals will be important for operation of spin-torque switched memories and domain wall devices in a wide temperature range. Here, we use the spin wave Doppler technique[1] to measure the temperature dependence of both the magnetization drift velocity $v(T)$ and the current polarization $P(T)$ in Ni$_{80}$Fe$_{20}$. We obtain these values from current-dependent shifts of the spin wave transmission resonance frequency for fixed-wavelength spin waves in current-carrying wires. For current densities of $10^{11}$ A/m$^2$, we obtain $v(T)$ decreasing from $4.8 \pm 0.3$ m/s to $4.1 \pm 0.1$ m/s and $P(T)$ dropping from 0.75$\pm$0.05 to 0.58$\pm$0.02 over a temperature range from 80 K to 340 K. [1] V. Vlaminck et al. Science 322, 410 (2008);