Magnetic oxides of spinel structure: Study of Co x Cu y Mn z O4 and Mg x Ni y Mn z O4 manganites (x+y+z=3)

Systematic studies in manganites of spinel structure have been undertaken. We report on the magnetic properties of two particular cases, in which one of the transition metals, Mg2+, is non-magnetic (NiMg x Mn2-x O4) or presents a stable oxidation state, Cu2+ (Co x Cu y Mn z O4, x+y+z=3). The magnetic behaviour is described with respect to varying contents of cobalt, copper or manganese. A ferrimagnetic transition is observed at 110-120 K, which depends on the cobalt content. Presence of copper increases the coercive field by a factor of ten with respect to the parent compound NiMn2O4