Browsing by Author "Freeland, JW"

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    Exchange bias in a columnar nanocrystalline Ni80Fe20/CoO thin film
    (The American Physical Society, 2007-12-28) van Lierop, J; Southern, BW; Lin, KW; Guo, ZY; Harland, CL; Rosenberg, RA; Freeland, JW
    The effects of interfacial coupling at the boundary of ferromagnetic and antiferromagnetic components in a nanoscale columnar-structured thin film of Ni80Fe20/CoO have been examined. Field-cooling the film results in very different temperature dependences of the enhanced coercivity and exchange-bias shift of the hysteresis loop. The exchange-bias temperature dependence is well described by thermal fluctuations of the interfacial spins while the coercivity temperature dependence indicates that single-domain-like columns are being coherently rotated by the thermal fluctuations of the interface spins. Furthermore, only a portion of the spins in the antiferromagnetic layer seem to be associated with the spin coupling that results in exchange bias. X-ray magnetic resonant scattering measurements show clearly the presence of canted Co interfacial moments that provide a local field which enables exchange bias at a significantly higher temperature than the onset of an enhanced coercivity. © 2007, American Physical Society
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    Spatial fluctuations of loose spin coupling in CuMn/Co multilayers
    (American Physical Society, 2011-09-12) Saerbeck, T; Loh, NA; Lott, D; Toperverg, BP; Mulders, AM; Rodriguez, AF; Freeland, JW; Ali, M; Hickey, BJ; Stampfl, APJ; Klose, F; Stamps, RL
    A detailed investigation of magnetic impurity-mediated interlayer exchange coupling observed in Cu(0.94)Mn(0.06)/Co multilayers using polarized neutron reflectometry and magnetic x-ray techniques is reported. Excellent descriptions of temperature and magnetic field dependent biquadratic coupling are obtained using a variant of the loose spin model that takes into account the distribution of the impurity Mn ions in three dimensions. Positional disorder of the magnetic impurities is shown to enhance biquadratic coupling via a new contribution J(2)(fluct), leading to a temperature dependent canting of magnetic domains in the multilayer. These results provide measurable effects on RKKY coupling associated with the distribution of impurities within planes parallel to the interfaces.© 2011, American Physical Society