Frequency and temperature dependence of ferromagnetic linewidth in exchange biased Permalloy

Ferromagnetic resonance linewidths were measured at 9.5 and 35 GHz and in t he temperature range from 77 to 350 K for thin Permalloy (Py) films exchang e biased by adjacent layers of NiO, CoO, or IrMn. Compared to unoxidized Py alone, for which the linewidth is nearly temperature independent in this r ange and scales linearly with frequency, exchange biased Py has broader lin es with distinctive temperature dependences for each bias material at 9.5 G Hz. Different temperature dependences were observed at 35 GHz. Our results are consistent with relaxation related to thermally driven reversal of the antiferromagnetic grains. Intrinsic damping and inhomogeneities also add to the widths. The qualitative features of the temperature and frequency depe ndences of the linewidths can be described with the usual expression for th e slow relaxation linewidth mechanism. The temperature dependence of the re laxation time is taken from Neel's expression for the reversal time using a ppropriate rate prefactors and activation energies. (C) 2001 American Insti tute of Physics.