High temperature structural and magnetic properties of cobalt nanorods

We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles (similar to 10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by mu H-o(C)=2(K-MC+K-shape)/M-S with K-MC the magnetocrystalline anisotropy constant, K-shape the shape anisotropy constant and M-S the saturation magnetization. H-C decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K. the magnetic properties are irreversibly altered either by sintering or by oxidation. (C) 2012 Elsevier Inc. All rights reserved.