Browsing by Author "van Lierop, J"

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    Correlating uncompensated antiferromagnetic moments and exchange coupling interactions in interface ion-beam bombarded Co90Fe10/CoFe-oxide bilayers
    (IOP Publishing LTD, 2012-11-01) Shueh, C; Chen, PS; Cortie, DL; Klose, F; Chen, WC; Wu, TH; van Lierop, J; Lin, KW
    The coercivity and exchange bias field of ferro-/antiferromagnetic Co(90)Fe(10)/CoFe-oxide bilayers were studied as function of the surface morphology of the bottom CoFe-oxide layer. The CoFe-oxide surface structure was varied systematically by low energy (0-70 V) Argon ion-beam bombardment before subsequent deposition of the Co(90)Fe(10) layer. Transmission electron microscopy results showed that the bilayer consisted of hcp Co(90)Fe(10) and rock-salt CoFe-oxide. At low temperatures, enhanced coercivities and exchange bias fields with increasing ion-beam bombardment energy were observed, which are attributed to defects and uncompensated moments created near the CoFe-oxide surface in increasing amounts with larger ion-beam bombardment energies. Magnetometry results also showed an increasing divergence of the low field temperature dependent magnetization [Delta M(T)] between field-cooling and zero-field-cooling processes, and an increasing blocking temperature with increasing ion-beam bombardment energy. © 2012 IOP Publishing LTD.
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    The effect of single crystalline substrates and ion-beam bombardment on exchange bias in nanocrystalline NiO/Ni80Fe20 bilayers
    (Institute of Electrical and Electronics Engineers (IEEE), 2013-12-23) Cortie, DL; Shueh, C; Lai, BC; Pong, PWT; van Lierop, J; Klose, F; Lin, KW
    Methods to modify the magnetic coercivity and exchange bias field of nanocrystalline antiferromagnetic/ferromagnetic NiO/Ni 80 Fe 20 thin films were investigated for bilayers grown using ion-assisted deposition onto different single crystalline substrates. An enhanced coercivity was found at 298 K for the films deposited on single crystalline MgO (100) and Al 2 O 3 (11-20) substrates. After field cooling the films to 50 K, the NiO/NiFe bilayer grown on Al 2 O 3 (11-20) exhibited the largest exchange bias ( - 25 Oe). The second part of the study investigated ion-beam modification of the ferromagnetic surface prior to the deposition of the NiO layer. A range of ion-beam bombardment energies (V EH ) were used to modify in situ the NiFe surface during the deposition of NiO/NiFe/SiO 2 films. Cross-sectional transmission electron microscopy showed a systematic reduction in the thickness of the NiFe layers with increasing Ar + bombardment energies attributed to etching of the surface. In addition, the bombardment procedure modified the magnetic exchange bias of the composite structure in both the as-prepared and field-cooled state. © 2013 IEEE
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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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    The magnetic interfacial properties of an exchange biased nanocrystalline Ni80Fe20/α-Fe2O3 bilayer studied by polarized neutron reflectometry and Monte Carlo simulation
    (Institute of Physics, 2019-11-22) Causer, GL; Cortie, DL; Callori, SJ; Manna, PK; van Lierop, J; Lee, YJ; Wang, XL; Lin, KW; Klose, K
    The strength of exchange bias can be influenced by interface roughness and antiferromagnetic morphology. Here, we studied the interface profile of an exchange biased, nanocrystalline Ni80Fe20/α-Fe2O3 bilayer. Magnetometry determined the bilayer's exchange bias is observed below a blocking temperature of 75 K. Polarized neutron reflectometry measurements revealed the Ni80Fe20 layer was fully saturated to yield a net-moment of 0.95 μB/atom, while the majority of the Fe2O3 layer exhibited zero net-magnetization with the exception of the interfacial region with an uncompensated moment between 0.5 and 1.0 μB/Fe2O3. Monte Carlo simulations of a ferromagnetic/antiferromagnetic bilayer incorporating a granular antiferromagnet indicate that an extrinsic uncompensated moment of ∼1.0 μB/Fe2O3 can arise from grain boundary disorder. The size of the modeled moment is equivalent to the experimental value, and comparable with previous calculations. Furthermore, unlike intrinsic uncompensated spins, it is found that the disorder-induced moment in the granular antiferromagnet is not destroyed by interface roughness. © 2019 The Japan Society of Applied Physics
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    Modulating the magneto-crystalline anisotropy and the exchange bias field in CoFe/(Co,Fe)O bilayers using ion-beam bombardment and single crystalline substrates
    (Institute of Electrical and Electronics Engineers Inc, 2012-11-01) Shueh, C; Cortie, DL; Klose, F; van Lierop, J; Lin, KW
    We report the effects of ion-beam bombardment on the room temperature and low temperature magnetic properties of ferromagnetic CoFe/antiferromagnetic (Co,Fe)O thin film bilayers. The films were deposited onto amorphous SiO(2) and single crystalline MgO(110)/(100) substrates. Magnetometry showed that ion-beam bombardment was capable of modifying the coercivity and loop shape for the thin film system at room temperature, corresponding to alteration of the effective magneto-crystalline anisotropy field. After field cooling to 50 K, a shifted hysteresis loop was seen for those films containing a proportion of the antiferromagnetic rock-salt (Co,Fe)O phase, with an exchange bias magnitude that depended on the ion-beam bombardment conditions. Our results indicate that matching the substrate with appropriate ion-bombardment conditions provides a promising way to engineer selectively two important types of magnetic anisotropy in ferromagnetic/antiferromagnetic bilayers: magneto-crystalline and exchange bias. © 2012, Institute of Electrical and Electronics Engineers (IEEE).