Reentrant spin-glass behaviour in highly frustrated Mn-rich spinel zinc manganate.

The present work offers an insight into the magnetic properties of Mn-rich spinel zinc manganate. Rietveld refinement reveals the formation of ZnMnO where Zn and Mn ions are randomly distributed in the tetrahedral sublattice. DC and AC susceptibility measurement of ZnMnO infers the occurrence of two kinds of transition below 11 K. Paramagnetic to ferrimagnetic transition occur at 10.7 K and ferrimagnetic to spin glass-like transition occurs at 5.8 K. The long-range canted ferrimagnetic ordering is corroborated using modified Lotgering model and calculated the exchange interaction values (J = 5.2 K,J = 5.3 K, J = 14.8 K). Further, the observed shift in freezing temperature with DC magnetic field obeys Almeida-Thouless behaviour and frequency dependence of AC susceptibility follows Vogel-Fulcher law. However, the complete establishment of the canonical spin glass state is denied since the manganese ions occupied at the tetrahedral site is equal to the percolation threshold (=33%). Subsequently, the observed spin glass-like behaviour (5.8 K) below Curie temperature (10.7 K) evidences the reentrant spin glass nature. Similarly, the strong frustration in ZnMnO lattice is observed through the substantial negative value of Curie-Weiss temperature (∼-599 K) and very high frustration factor (f = 56). Overall, the chosen ZnMnO is a highly frustrated magnetic system revealing re-entrant spin-glass behaviour.