One of the puzzles of the recent investigations on the exchange anisotropy in ferromagnetic (FM)/antiferromagnetic (AF) bilayers is the fact that different techniques yield different values for the exchange field (HE) between the layers. We report an investigation on sputtered NiFe/NiO carried out with three different techniques, namely, magneto-optical Kerr effect magnetometry (MOKE), Brillouin light scattering (BLS), and ferromagnetic resonance (FMR). In an attempt to reconcile the measurements obtained with the various techniques, we interpret the data with a model that includes the formation of a planar domain wall in the AF layer, giving rise to a torque on the FM moment represented by an effective domain wall field (HW). We find out that while the same pair of values of HE and HW provide equally good fits to the reversible FMR and BLS measurements, different pairs are necessary to fit the irreversible magnetometry data.

In-plane ferromagnetic resonance (FMR) has been used to study the room-temperature linewidth ΔH of single crystal Fe films grown by dc magnetron sputtering onto MgO(100) substrates. Several samples were grown with the film thickness in the range 70 Å<tFe<250 Å. The measurements were carried out in the frequency range from 7.0 to 12.3 GHz. A phenomenological model for the FMR linewidth was developed that includes simultaneous effects due to intrinsic damping and angular dispersions of the cubic and uniaxial axes of anisotropy. These angular dispersions are found to be responsible for the relatively larger linewidths observed as a function of the in-plane field direction with fixed frequency, and as a function of frequency for the easy and hard directions as well. The behavior of the linewidth with the film thickness can be described by a sum of a constant volume term plus a term proportional to 1/tFe, representing the relaxation due to the misfit dislocations.

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Exchange bias of NiO/NiFe: Linewidth broadening and anomalous spin-wave damping J. Appl. Phys. 93, 7723 (2003); 10.1063/1.1557964 Kerr observations of asymmetric magnetization reversal processes in CoFe/IrMn bilayer systems

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