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Experimental Methods

NiO (50 nm)/NiFe (10 nm) bilayers were grown by ion beam sputtering onto single crystal (001) MgO and onto polycrystalline Si substrates.[7] NiFe (50 nm) films grown onto (001) MgO or onto Si without NiO buffers were also prepared. Both uniaxial (in NiFe films) and unidirectional (in NiO/NiFe films) anisotropy was induced during deposition by means of permanent magnets producing a uniform bias field, µ0H = 30 mT in the plane of the substrate. In this paper we will examine films where this bias field was along either the <110> or <100> sample direction.

Macroscopic hysteresis loops of the films were measured at room temperature with a vibrating sample magnetometer (Figure 1). Optical reflecting microscopy and a photoelasticity method[8] were used to reveal the crystal lattice defects in the films. The magnetization reversal processes in the samples were studied using the magneto-optical indicator film (MOIF) technique.[9] This latter technique utilizes a Bi-substituted iron garnet film with in-plane anisotropy, which is placed on the sample. Polarized light passes through the indicator film and is reflected back by an Al underlayer covering the bottom surface of the film. The polarization of the passed light experiences a Faraday rotation through an angle proportional to the component of the local magnetic field parallel to the light propagation direction. When the polarizing prisms in the microscope are slightly uncrossed the bright or dark variations of the image represent the variations of the stray field component pointed up or down. The resulting Faraday portrait contains information about the domain structure as well as about defects in the crystal structure which affect the spin distribution in the sample.


alchaiken@gmail.com (Alison Chaiken)
Sat Feb 7 13:25:48 PST 1998