Temperature dependence of the switching field in all-perpendicular spin-valve nanopillars

We present temperature dependent switching measurements of the Co/Ni multilayered free element of 75-nm-diameter spin-valve nanopillars. Angular dependent hysteresis measurements as well as switching field measurements taken at low temperature are in agreement with a model of thermal activation over a perpendicular anisotropy barrier. However, the statistics of switching (i.e. the mean switching field and the variance of the switching field distribution) from 20 up to 400 K are in disagreement with a Neel-Brown model that assumes a temperature independent barrier height and anisotropy field. We introduce a modified Neel-Brown model that fits the experimental data in which we attribute a T-3/2 dependence to the barrier height and the anisotropy field due to the temperature dependent magnetization and anisotropy energy.