Browsing by Author "Shueh, C"

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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 nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry
    (American Physical Society, 2012-08-07) Cortie, DL; Lin, KW; Shueh, C; Hsu, HF; Wang, XL; James, M; Fritzsche, H; Brück, S; Klose, F
    We investigated a hematite alpha-Fe2O3/permalloy Ni80Fe20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Neel temperature of bulk alpha-Fe2O3 is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5-1.0 mu(B) per Fe atom within a depth of 1-2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains. © 2012, American Physical Society.
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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).