Influence of thermal fluctuations on the emission linewidth in MgO-based spin transfer oscillators

The temperature dependence of the microwave emission linewidth Delta f, the amplitude-phase coupling parameter nu, and the amplitude relaxation rate Gamma(p) were investigated experimentally for tunnel junction spin-transfer-oscillators. A linear increase of Delta f and unexpectedly of Gamma(p) with temperature is observed, giving a ratio 2 pi Delta f/Gamma(p), close to one. Analytical evaluation of the phase variance confirms that for this ratio the temperature dependence of Delta f is linear and that in this temperature range Delta f is enhanced by the amplitude-phase coupling. This is not changed when taking the temperature dependence of Gamma(p) into account, the origin of which remains to be elucidated. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4744924]