Preparation-dependent properties of Ca(Cu,Mn)7O12 CMR materials

Both magnetic ordering temperatures and lattice constants were observed to be a function of preparation temperature for single-phase CaCuMn6O12 CMR ceramics of the same cation, oxygen composition and crystal structure. It was found for the first time that higher preparation temperatures Tprep result in a linear increase of a cubic cell parameter a, Δa/ΔTprep∼4×10−5Å/∘C, and in a sharp decrease of magnetic ordering temperatures Tcrit, by about ΔTcrit/ΔTprep∼3/5, for quenched samples. High resolution NPD experiments have shown the presence of antisite defects resulting in partial occupation of octahedral (8c) sites by Cu2+ at higher preparation temperatures as never assumed for an ideal structure. The data obtained give a new insight to the problem of functional properties reproducibility suggesting stronger requirements for the production control of CMR materials.