The temperature dependence of coercivity for Ni nanowires: possible effect of NiO antiferromagnetic clusters

Abstract A study about coercivity as a function of the temperature is presented for nickel nanowires in porous alumina membranes. Changes in coercivity values in temperatures between 50 K and 300 K and results by X-ray diffraction (XRD) suggest that, the effects are motivated by the antiferromagnetic phase transition of small clusters of nickel oxide on the nanowires surface. This is supported by the temperature range at which the antiferromagnetic transition of NiO occurs and the possibility of interaction Ni/NiO by exchange coupling. The temperature value for spontaneous antiferromagnetic ordering of NiO, decreases with the diminution of the clusters size. The lower Neel temperature reported for these clusters is 50 K, which is in agreement with the coercivity diminution presented in the present paper. The effects of magnetostriction, magnetocrystalline anisotropy and dipolar interactions coexist with our proposal (local pinning due to exchange), giving a high complexity to the coercivity temperature behavior of these nanowires. Finally, our hypothesis was corroborated by the XRD analysis, confirming the existence of peaks belonging to the Ni and NiO phases.