Spin Transfer Precessional Dynamics in Co60Fe20B20 Nanocontacts
William H. Rippard, Matthew R. Pufall, Michael L. Schneider, Kevin Garello, Stephen E. Russek
We report on the precessional dynamics in spin transfer oscillators having Co60Fe20B20 free layers as a function of annealing time at 225 °C. Repeated annealing reduces the critical current Ic by roughly a factor of 3 and increases the tunability of the oscillation frequency with current df/dI. The decrease in Ic correlates with an increasing giant magnetoresistance (GMR) during the first 3 h of annealing. For longer times, df/dI continues to increase, although the GMR does not. The variations in the macroscopic Co60Fe20B20 magnetization parameters and contact dimensions with annealing are not sufficient to account for the later changes.