Possible half-metallicity and suppressed double-exchange interaction in spinel Mn2.4Ni0.6O4: A Ni-substitution effect

Abstract

In this work, we present detailed structural, magnetic, dielectric, and transport properties as well as electronic structure studies of a Mn2.4Ni0.6O4 system. The Mn2.4Ni0.6O4 system acquires cubic Fd3̅m crystal structure at room temperature and exhibits a ferrimagnetic transition around 108 K. The pristine Mn3O4 acquires a tetragonal I41/amd structure at room temperature and exhibits ferrimagnetic transition and magneto-dielectric coupling at around 43 K. The magneto-dielectric coupling is found to be absent in cubic Mn2.4Ni0.6O4, but still shows interesting transport behavior. The resistivity results show semiconducting behavior of the system, but interestingly, this semiconducting behavior weakens at low temperatures. This is evident from the decreased rate of change of resistivity with decreasing temperature. X-ray absorption spectra results have confirmed that to compensate for the charge imbalance caused by Ni2+ cations at the octahedral-site, a few Mn3+ cations transform into Mn4+. The density of state calculations reveal that at Fermi-level, Mn2.4Ni0.6O4 exhibits small but finite bands in the majority channel while a band gap of 1.5 eV exists in the minority channel. The ground state electronic structure of Mn2.4Ni0.6O4 predicts a half-metallic character for the system. The partial density of states analysis of Mn2.4Ni0.6O4 suggests that the bands near the Fermi-level are predominantly contributions of Mn3+, Mn4+ and O2-. We further discuss the origin of the weak semiconducting behavior of Mn2.4Ni0.6O4 at low temperatures.