Observation of the ferromagnetic domain structure in exchange-coupled antiferromagnetic/ferromagnetic thin films (abstract)

Abstract

Exchange-coupled antiferromagnetic/ferromagnetic (AFM/FM) thin films are known to exhibit many interesting and potentially useful properties, including a unidirectional anisotropy.1 Despite nearly three decades of research, the nature of the AFM/FM interface exchange interaction is still not well understood, particularly in polycrystalline thin films. Simple predictions suggest an exchange-coupling strength 10–100 times stronger than generally observed. The models of Mauri et al.2 and Malozemoff3 resolve this inconsistency by considering domains and reversal within the AFM layer. Clearly, to understand this phenomena we need an accurate description of the AFM’s bulk and interface spin structure and its action under the influence of a coupled FM film. In an effort to better understand the AFM/FM system, we have been studying NiO/NiFe. In this report, we examine the magnetic domain structure and reversal process in the NiO/NiFe system by imaging of the NiFe magnetic domain structure. This is accomplished using our newly developed Kerr microscope. This microscope uses a phase detection method that allows high spatial resolution (0.5 μm) and good magneto-optic contrast. In addition, we can discriminate the magnetization vector components in the sample plane to develop a vector map of the magnetization. Kerr images indicate that the magnetic domain structure in the NiFe is complicated by the NiO interaction. The magnetization assumes a large scale “ripplelike” structure with domains walls perpendicular to the easy direction. This surprising result may result from a local dispersion in the NiO pinning direction. We will present a simple model of this interaction and relate it to the other current standard models.