Temperature Dependence of Thermally Activated Ferromagnetic Resonance in Tunneling Magnetoresistive Heads

Temperature dependence of thermally activated ferromagnetic resonance (FMR) has been studied for two kinds of tunneling magnetoresistive (TMR) heads with a track width of about 100 nm. It is found that the power spectral density (PSD) is composed of a FMR peak and a resonance kink at slightly lower frequency. For the TMR head with a well-defined magnetization state (single domain) of the free layer, the kink is much smaller than the peak in amplitude, and the FMR peak increases in its amplitude and shifts to lower frequency as temperature increases. However, for the TMR head with a hysteretic magnetization behavior, the FMR peak is blurred by the kink and no discernible shift of its position can be detected as temperature increases. It is observed that the noise power can be redistributed among different resonance modes at different temperatures and fields