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.