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, ?AF? 4.8 10?6 emu?g?1?Oe?1, is also observed for these single phase CuO nanoparticles, while for bulk CuO, ?AF ? 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 (?AF ? 5.1 10?6 emu?g?1?Oe?1 for 34 % Cu2O), but then, it gets reduced (?AF ? 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.

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