Low-temperature magnetic ordering in Co core/CoO shell nanoparticles on the copper surface

Abstract

Cobalt/cobalt oxide nanoparticles electrochemically deposited onto a copper surface revealed an unusual behavior of the coercivity and exchange bias at liquid helium temperature [V.G. Bayev et al., Appl. Surf. Sci. 440 (2018) 1252–1260], pointing out the necessity of careful consideration of magnetic properties at these temperatures. Here, it is shown that the approach based on the random anisotropy model and analysis of law of the approach to magnetic saturation adopted for the two-dimensional (2D) magnetic system allows obtaining the correlation function of the magnetic anisotropy axes in real space, as well as the exchange, random and coherent anisotropy magnetic fields. The long-range correlation in the magnetic anisotropy axes and the oscillating character of the correlation function is the characteristic feature, suggesting the important role of the interplay between the exchange bias and random anisotropy on the one hand and indirect exchange coupling via the conducting electrons of copper and magnetic dipole interaction, on the other.