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 Mn_3−xZn_xO₄ 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.