Element-specific study of the coupled magneto-structural and magneto-electronic properties of CoNi nanoarrays
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RESEARCH PAPER
Element-specific study of the coupled magneto-structural and magneto-electronic properties of CoNi nanoarrays Chao-Yao Yang • Yuan-Chieh Tseng Hong-Ji Lin
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Received: 13 December 2012 / Accepted: 24 February 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract The magneto-structural (MS) and magneto-electronic (ME) effects, as well as their coupling relationship, were investigated in electroless-plated (EL) Co0.5Ni0.5 arrays treated by post N2 annealing and in situ field plating. Separately and combined, these two treatments have been widely employed to improve the properties of magnetic nanostructures. This work aimed to discriminate between treatments with respect to electronic and structural properties, and magnetic degrees of freedom of Co0.5Ni0.5 nanostructures. The field-plated sample exhibited a strong MS– ME coupling due to magneto-crystalline anisotropy (MCA), arising from a FCC (111) preferred orientation with lattice planes stacking orthogonally to the long axial direction of the arrays. A large coercivity was observed in this structure, arising from high magnetic stability. X-ray magnetic circular dichroism revealed that magnetization was enhanced primarily by Co magnetism, while the field-plated sample underwent a MS/ME transition with corresponding increase of the plating field. Conversely, the
heat-treated sample comprised isotropically oriented nanocrystals approximately 20 ± 3 nm in diameter, coated with an oxidation layer (approximately 5 ± 2 nm thick). The absence of MCA in these samples ensured a weak MS–ME coupling. Although the Ni magnetization of heat-treated samples remained close to that of the field-plated sample, the Co constituent exhibited CoO and Co3O4 phases in addition to the metallic state. By contrast, the Co constituent of the field-plated sample was mainly metallic. The lack of MCA, combined with a complex Co magnetic state, appears responsible for the divergent macroscopic magnetic behaviors of the heattreated and the field-plated samples. By isolating changes in local magnetic moments of Ni and Co, we gained a fundamental understanding of the effects of post-N2 annealing and field plating on CoNi. Such knowledge may assist researches in improving the magnetic properties of bimetallic nanostructures. Keywords Nanoarrays CoNi XMCD Electroless Magneto-crystalline anisotropy
C.-Y. Yang Y.-C. Tseng (&) Department of Materials Science & Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30010, Taiwan, ROC e-mail: [email protected]
Introduction
H.-J. Lin National Synchrotron Radiation Research Center, Taiwan, 101 Hsin Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan, ROC
CoxNi1-x is ubiquitously used in magnetism studies (Yang et al. 2011; Yamauchi et al. 2004; Sankara et al. 2003; Qin et al. 2002; Ohtake et al. 2009;
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Pane´ et al. 2007; Go´mez et al. 2005; Ga´lvez et al. 2010; Kuepper et al. 2011). Having a naturally high atomic moment and coercivity, Co promotes the magnetization and
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