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Magnetization Process in Vortex-imprinted Ni80Fe20/Ir20Mn80 Square Elements

Journal of Magnetics, Volume 16, Number 2, 30 Jun 2011, Pages 83-87
H. Xu (Dept. of Physics and Astronomy, University of Victoria), J. Kolthammer (Dept. of Physics and Astronomy, University of Victoria), J. Rudge (Dept. of Physics and Astronomy, University of Victoria), E. Girgis (Dept. of Physics and Astronomy, University of Victoria), B. C. Choi * (Dept. of Physics and Astronomy, University of Victoria), Y. K. Hong (Dept. of Electrical and Computer Engineering, The University of Alabama), G. Abo (Dept. of Electrical and Computer Engineering, The University of Alabama), Th. Speliotis (Institute of Materials Science, NCSR “Demokritos,”), D. Niarchos (Institute of Materials Science, NCSR “Demokritos,”)
Abstract
The vortex-driven magnetization process of micron-sized, exchange-coupled square elements with composition of Ni80Fe20 (12 nm)/Ir20Mn80 (5 nm) is investigated. The exchange-bias is introduced by field-cooling through the blocking temperature (TB) of the system, whereby Landau-shaped vortex states of the Ni80Fe20 layer are imprinted into the Ir20Mn80. In the case of zero-field cooling, the exchange-coupling at the ferromagnetic/antiferromagnetic interface significantly enhances the vortex stability by increasing the nucleation and annihilation fields, while reducing coercivity and remanence. For the field-cooled elements, the hysteresis loops are shifted along the cooling field axis. The loop shift is attributed to the imprinting of displaced vortex state of Ni80Fe20 into Ir20Mn80, which leads to asymmetric effective local pinning fields at the interface. The asymmetry of the hysteresis loop and the strength of the exchange-bias field can be tuned by varying the strength of cooling field. Micromagnetic modeling reproduces the experimentally observed vortex-driven magnetization process if the local pinning fields induced by exchange-coupling of the ferromagnetic and antiferromagnetic layers are taken into account.
Keywords: exchange bias; vortex magnetization; magneto-optics; micromagnetic modeling
DOI: 10.4283/JMAG.2011.16.2.083
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