Hydrothermal synthesis of crednerite CuMn_1−x M _x O₂ (M = Mg, Al; x = 0–0.08): structural characterisation and magnetic properties

A series of CuMn_1−x M _x O₂ (M = Mg, Al; x = 0–0.08) samples was prepared using the low-temperature hydrothermal method. Crednerite-type materials are obtained for a low level of substitution, i.e. up to x = 0.08, and transmission electron microscopy observations indicate that the average crystallite size decreases with an increase in x. The evolution of unit cell parameters in function of x, from Rietveld refinements using X-ray powder diffraction data, presents a distinct behaviour for both series, but corresponds in both cases to a regularisation of the triangular network in the (a, b) plane. The investigation of the structural, thermal and magnetic properties reveals that the substitution has a significant role on the magnetism in CuMn_0.94M_0.06O₂ (M = Mg, Al). It was found that the Mg and Al substitution on the Mn site leads to a small increase in the magnetisation values at low temperature, although the particle size decreases, which can be related to a release of magnetic frustration.