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The exchange bias anisotropy field in CoFe/IrMn ferromagnetic/antiferromagnetic bilayers has been investigated by two different experimental probes. One was the traditional hysteresis loop shift technique and the other was a recently developed technique which monitors small reversible rotations of the magnetization with the anisotropic magnetoresistance (AMR). All the samples show approximately twice the exchange bias anisotropy field measured with the AMR technique compared to that measured with the traditional hysteresis loop method. Based on similar experiments in other materials, there is a portion of the exchange bias uniaxial anisotropy which rotates in a hysteresis loop measurement. It is surmised it is this energy which the hysteresis loop technique neglects and that the AMR technique is a better measure of the exchange bias anisotropy energy.

We have investigated a nonsymmetric bottom giant magnetoresistance spin valve with the structure Si/NiO/Co/Cu/Co/Ta, as well as single ferromagnetic Co layers on antiferromagnetic NiO, with or without a nonmagnetic Cu spacer. Magnetic hysteresis loops have been measured by SQUID magnetometry, and magnetic domain structures have been imaged using an advanced magneto-optical indicator film (MOIF) technique. The MOIF technique demonstrated that the first stage of magnetization reversal is characterized by nucleation of many microdomains. With increasing reversed field, the domain walls move over small distances (5–20 μm) until annihilation. The domain size was observed to increase with the thickness of the Co layer. When an alternating magnetic field was applied, the domain structure was dramatically changed.

We report on a combined theoretical and experimental study of the magnetic microstructure of a single component, single phase, Pore-free nanocrystalline ferromagnetic material. From the equations of micro-magnetics we conclude that the magnetic microstructure is the convolution product of an anisotropy field microstructure and of a response function with a correlation length lH that depends on the applied field Ha. We derive equations for small angle neutron scattering by such structures, and present experimental scattering data for electrodeposited nanocrystalline Ni, the first where for a wide range of Ha the dominant scattering contribution is from the purely magnetic microstructure, not from nuclear or magnetic contrast at pores or second phases. The variation of the scattering cross section with Ha is in excellent agreement with the theory, indicating that the underlying changes in the magnetic microstructure with Ha are not displacements of domain walls, but changes in lH and hence in the magnetic response to an entirely stationary anisotropy field microstructure. At 20K the anisotropy fields are dominated by magnetocrystalline anisotropy, but at 300K the perturbation is from a much stronger interaction which maintains some moments aligned antiparallel to the field direction at Ha as high as 1.4MA/m (18kOe).

The magnetic behavior of giant magnetostrictive TbFe/FeCo multilayers show that individual layers of as-deposited multilayers in their demagnetized state are single domain due to stray-field coupling between adjacent layers. Such multilayers do not show a collective behavior during magnetization reversal. In contrast, stress-free films obtained by annealing at 543 K for 1 h subdivide themselves into multiple domains to lower their overall energy, and show a collective magnetization behavior. An interesting observation is the dynamic formation and collapse of magnetoelastically induced domains in TbFe layers in annealed multilayers during reversal.

Experimental measurements of the aftereffect along a magnetization reversal curve are compared with the predictions of a Preisach-Arrhenius model for a high density particulate recording medium. The Preisach parameters are determined from the measurement of the major hysteresis loop and the remanence loop. The Arrhenius parameters were determined from a single aftereffect curve. It was then found that the model gives good qualitative agreement with both the initial slope and, for the case in which the aftereffect is not monotonic, the peak value of the aftereffect.