Dielectric constant of multiferroic pure and doped CuO nanoparticles

Within a microscopic model and a Green׳s function technique we have calculated the temperature and magnetic field dependence of the dielectric function ϵ ( T , H ) in CuO nanoparticles (NPs) taking into account frustration, single-ion anisotropy, s–d coupling, spin–phonon interaction and linear magnetoelectric coupling. ϵ ( T ) shows weak and broad anomalies at the two magnetic phase transition temperatures TN 2 and TN 1 due to the magnetoelectric coupling. ϵ ( H ) decreases with increasing of H and the kinks disappear. The changes of ϵ with ion doping are discussed. Comparisons to experimental data are made.