Suppression of ferromagnetic order in CuO/Cu2O nanocomposites

Abstract

11 nm diameter quasi-spherical and single phase CuO/Cu2O nanocomposites, with varying CuO:Cu2O ratio, were synthesized using solvothermal process. X-ray diffraction patterns refined with the Rietveld method show an evolution of the CuO:Cu2O ratio ( %) for the three samples (100:0, 66:34, and 9:91), along with an increased lattice deformation of the CuO unit cell as the amount of Cu2O increased: a = 4.653(2) Å, b = 3.411(1) Å, and c = 5.131(1) Å for the single phase CuO nanoparticles, similar to bulk, while a = 4.727(2) Å, b = 3.457(3) Å, and c = 5.247(2) Å for the 9/91 % CuO/Cu2O nanocomposites. Magnetic measurements as a function of the temperature (M vs T) and as a function of the magnetic field (M vs H) nanoparticles indicated the presence of a ferromagnetic phase in the whole range of temperatures for the single phase CuO nanoparticles, as revealed by the persistent hysteresis observed in the M vs H loops. In addition, an enhanced antiferromagnetic contribution, denoted by the increase in the antiferromagnetic susceptibility, χAF∼ 4.8 10−6 emu∙g−1∙Oe−1, is also observed for these single phase CuO nanoparticles, while for bulk CuO, χAF ∼ 0.6 10−6 emu∙g−1∙Oe−1. With increasing Cu2O content (≥ 34 % Cu2O), the ferromagnetic phase is drastically suppressed for all temperatures, whereas the antiferromagnetic contribution at low temperatures (2–5 K) first increases (χAF ∼ 5.1 10−6 emu∙g−1∙Oe−1 for 34 % Cu2O), but then, it gets reduced (χAF ∼ 1.46 10−6 emu∙g−1∙Oe−1 for 91 % Cu2O). These magnetic changes showcase the relevance of the interface effects introduced by the Cu2O phase in CuO/Cu2O nanocomposites.