Temperature dependence of ferromagnetic resonance as induced by NiO pinning layers

Ferromagnetic resonance (FMR) experiments have been conducted near 9.5 GHz on permalloy (Py) thin films which are components of spin valves and relate d structures. These so-called giant magnetoresistance structures often use antiferromagnetic NiO to achieve pinning of one magnetic layer. Magnetic an isotropies acting on these pinned layers were deduced by observing their re sonances for fields perpendicular to and in the sample plane. We used data taken from 4 to 600 K to identify potential mechanisms of pinning, anisotro py, and linewidth. The anisotropic exchange pinning and an isotropic downwa rd FMR shift vanish at a blocking temperature well below the bulk Neel temp erature of NiO. The strong temperature dependencies of the isotropic shift and linewidth may reflect the presence of different spin pinning subsystems and the different time scales of the FMR and low frequency or static measu rements.