TEMPERATURE DEPENDENCE OF CURRENT POLARIZATION IN Ni₈₀Fe₂₀ BY SPIN WAVE DOPPLER MEASUREMENTS

Meng Zhu^1,2, Cindi. L. Dennis³, R. D. McMichael¹

¹ Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899

² Maryland NanoCenter, University of Maryland, College Park, MD 20742

³ Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, MD 20899

The current polarization P in ferromagnetic metals describes the difference between currents carried by spin-up and spin-down electrons.  P is an important quantity for development of spin-torque switched memories and devices based on the control of current-induced domain wall motion.   The temperature dependence of P will be important for successful application of these technologies 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 current-carrying Ni₈₀Fe₂₀ wires.  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 10¹¹A/m², we obtain v(T) decreasing from 4.8 ± 0.3 m/s to 4.1 ± 0.1 m/s and P(T) dropping from 0.75 ± 0.05 to 0.58 ± 0.02 over a temperature range from 80 K to 340 K. This work has been supported in part by the NIST-CNST/UMD-NanoCenter Cooperative Agreement.

[1] V. Vlaminck et al. Science 322, 410 (2008);