• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.176-181
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• 2003

The magnetic domain walls at the edges of a large patterned and exchanged-biased NiO(10-60 nm)/NiFe(10 nm) bilayers and their motions with applied field were investigated by magnetic force microscopy. Three kinds of domain walls, namely, head-to-head zig-zag and tail-to-tail zig-zag Bloch walls and straight Neel walls were found at specific edges of the unidirectional biased NiO(30 nm)/NiFe(10 nm) bilayer having the exchange biasing field (H$\sub$ex/) of 21 Oe. No walls were observed for the strong exchange-biased bilayer (60 nm NiO, H$\sub$ex/ = 75 Oe), while the amplitude of the zig-zag domain increased with decreasing exchange biasing. This may be explained by mutual restraint between H$\sub$ex/ and the demagnetization field of edge. We similarly investigated the magnetization reversal process, the subsequent motion of the walls and identified the pinning and nucleation sites during reversal.

• Journal of Magnetics
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• v.14 no.1
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• pp.36-41
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• 2009

Magneto-optical Kerr effect (MOKE) magnetometry was used to investigate magnetization reversal dynamics in 30-nm NiFe/15-nm FeMn, 15-nm FeMn/30-nm CoFe bilayers, and 30-nm NiFe/(2,10)-nm FeMn/30-nm CoFe trilayers. The in-plane magnetization components of each ferromagnetic layer, both parallel and perpendicular to the applied field, were separately determined by measuring the longitudinal and transverse MOKE hysteresis loops from both the front and back sides of the film for an oblique incident s-polarized beam. The magnetization of the FeMn/CoFe bilayer was reversed abruptly and symmetrically through nucleation and domain wall propagation, while that of the NiFe/FeMn bilayer was reversed asymmetrically with a dominant rotation. In the NiFe/FeMn/CoFe trilayers, the magnetic reversal of the two ferromagnetic layers proceeded via nucleation and domain wall propagation for 2-nm FeMn, but via asymmetric rotation for 10-nm FeMn. The exchange-biased ferromagnetic layers showed the magnetization reversal along the same path in the film plane for the decreasing and increasing field branches from transverse MOKE hysteresis loops, which can be qualitatively explained by the theoretical model of the exchange-biased ferromagnetic/antiferromagnetic systems.

• Journal of Magnetics
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• v.7 no.3
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• pp.94-97
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• 2002

The dependence on nickel oxide thickness and a ferromagnetic layer thickness in unidirectional and isotropic exchange-coupled NiO/NiFe(Fe) bilayer films was investigated by magnetic force microscopy to better understand the relation between magnetic domain structure and exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a cross type domain with out-of plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle.

• Journal of Magnetics
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• v.10 no.3
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• pp.113-117
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• 2005

Some polycrystalline ferromagnetic mms are composed of continuously connected nanometer scale islands with random crystallite orientations. The nanometer perturbations of the mm introduce a large number of nearly degenerate local field configurations that are indistiguishable on a macroscopic scale. As a first step, this situation is modelled as a thin ferromagnetic disc coupled by exchange and dipole interactions to a homogeneous ferromagnetic plane, where the disc and plane have different easy axes. The model is solved to find the partial $N\acute{e}el$ domain walls that minimize the magnetic energy. The two solutions give a bistable configuration that, for appropriate geometries, provides an important microsopic ferromagnetic degree of freedom for the mm. These results are used to interpret recent measurements of exchange biased bilayer films.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.224-227
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• 2004

We have studied local magnetization reversal by laser annealing in exchange biased NiFe/FeMn bilayer. Local magnetization reversal was performed by using the DPSS laser under external magnetic field of 600G. When the laser illuminated the patterned film with the power of above 300 mW during 15 min, a magnetoresistance (MR) curve with symmetric peaks at the opposite field was obtained due to the local reversal of exchange biasing. The direction of exchange anisotropy in the locally reversed region can be restored by local laser annealing under alternating magnetic field, even if its MR peak was reduced by the damage and interdiffusion. The magnetic domain structure of the locally reversed region was measured by MFM. The new domains were generated by laser annealing near the exposed area.