Stable cubic spinels in the Zn–Mn–O system in air

A part of the Zn–Mn–O phase diagram has been studied by using soft synthetic conditions and highly reactive precursors. This procedure allowed us to find and to isolate new single phases in the Zn-rich region. The new compounds are cubic spinels with a nominal composition Mn3−xZnxO4 with x=1.6 and 1.7. These spinels decompose upon heating giving rise to tetragonal distorted spinels. This survey is focused on the low-temperature region (T⩽700 °C) completing previous reports on the Zn–Mn–O phase diagram. We also report the magnetic properties of the new cubic spinels. These samples behave as paramagnets obeying a Curie–Weiss law in a broad temperature range. The effective paramagnetic moment agrees with the nominal mixture of Mn3+ and Mn4+ ions. However, randomness and competitive interactions give rise to the formation of spin-glass phases at very low temperature.