Experimental study of magnetization reversal processes in nonsymmetric spin valve

Abstract

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.

Asymmetry of domain nucleation and enhanced coercivity in exchange-biased epitaxial NiO/NiFe bilayers

“…16 A transparent Bi-substituted iron garnet indicator film with in-plane anisotropy is placed on top of the sample. Polarized light is passed through the indicator film and reflected by an Al underlayer.…”

Direct experimental study of the magnetization reversal process in epitaxial and polycrystalline films with unidirectional anisotropy

“…13 The MOIF technique is based on the Faraday rotation of linearly polarized light in an indicator film, a Bi-substituted iron garnet film with in-plane anisotropy, which is placed on the sample. The polarized light passes through the indicator film and is reflected back by an Al underlayer covering the bottom surface of the film, which is adjacent to the sample surface.…”

Real-time MOKE microscopy made simple

“…[9][10][11] However, this method generally suffers from a weak signal (defined as the imaging contrast between spin orientations), especially if time-resolved imaging is needed, which limits the use time-averaging or scanning-type setups for signal-to-noise ratio improvement purposes. The most common MOKE microscopy setups either employ MOKE in the polar geometry, giving larger sensitivity compared to the longitudinal or transverse geometries, or use the help of Magneto-Optic Imaging Films (MOIF) for signal enhancement [12]. However, the polar MOKE geometry can only record the magnetization component orthogonal to the film surface [13], while imaging the more common in-plane magnetization with MOIF [14,15] requires a magneto-optical transducer placed directly on top of the film surface, thus causing undesirable interference with the sample.…”