Nature of magnetism in copper-doped oxides: ZrO₂, TiO ₂, MgO, SiO₂, Al₂O₃, and ZnO

The nature of magnetism in 10% Cu-doped Zr O2, Ti O2, MgO, Si O2, and Al2 O3 is investigated using superconducting quantum interference device magnetometry and electron magnetic resonance (EMR). The doping was done by the incipient wetness impregnation technique. X-ray diffraction studies showed the presence of some CuO notably in Ti O2, Si O2, and Al2 O3. However, EMR yielded typical Cu2+ spectra in all the samples, resulting from some doping. Magnetic field (H) and temperature (T) dependences of the magnetization (M) show only paramagnetism in these oxides in contrast to ferromagnetism with Tc =380 K observed in CuZnO. Concentrations x of Cu2+ doped into the oxides are determined from the M vs T and M vs H data, showing CuZr O2 with the largest x and hence largest magnetization.