Magnetic properties in a partially oxidized nanocomposite of Cu-CuCl

Magnetism of a very thin antiferromagnetic (AFM) surface CuO has been investigated with partially oxidized nanocomposites of Cu-CuCl, similar to 200 nm. The samples are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, x-ray-excited Auger electron spectroscopy, transmission electron microscopy and magnetic measurements. The characterizations indicate that the composites have a core-shell structure. Before oxidation, it is (Cu) core/(CuCl) shell, and after oxidation it is (Cu) core/(Cu2O + CuCl + minute CuO) shell. The magnetic measurements have revealed that a ferromagnetic (FM)-like open hysteresis exists at temperatures below the freezing point, TF. In the high field region, a paramagnetic (PM) response appears without showing any sign of saturation. Also, the field dependent magnetization (M-H) measurement is PM-like at T > T-F. These interesting magnetic properties are shown to arise from the AFM CuO on the outer surface. They are attributed to the uncompensated surface spins of Cu2+ and the effect of random surface potential. More interestingly, the magnetic susceptibility is greatly enhanced in the presence of Cl- anions at T < T-F, according to the field-cooled/zero-field-cooled (FC/ZFC) measurements. This further supports the point that the disorder or frustration effect of the impurity would reduce the AFM ordering of CuO and increase the level of uncompensated spins.