Spin-glass transition in MnO

Abstract

What could possibly be new in MnO 46 years after the discovery of its antiferromagnetic transition?: a spin-glass transition in the (25-50)-K temperature range. The susceptibility of MnO powders obtained by various treatments (MnO aged 30 years in ambient atmosphere, ${\mathrm{MnO}}_{2}$ reduced at 500 and 1000\ifmmode^\circ\else\textdegree\fi{}C in hydrogen, and MnO heated in air at 500\ifmmode^\circ\else\textdegree\fi{}C) was measured in low dc and ac magnetic fields and in a high dc magnetic field. The spin-glass behavior is linked to a slight offstoichiometry: $\mathrm{Mn}{\mathrm{O}}_{1+x}$ with $x\ensuremath{\le}0.01$. It is not believed that the susceptibility peak arises from a mixture of MnO and ${\mathrm{Mn}}_{3}$${\mathrm{O}}_{4}$. This conclusion is based on the shape of the susceptibility curves at both the spin-glass temperature (${T}_{\mathrm{SG}}$) and the N\'eel temperature as well as on the various ${T}_{\mathrm{SG}}$ values which differ from the ferrimagnetic transition of ${\mathrm{Mn}}_{3}$${\mathrm{O}}_{4}$. It is more likely that the spin-glass interaction occurs either between ${\mathrm{Mn}}_{3}$${\mathrm{O}}_{4}$-like clusters or between defects typical in MnO such as an interstitial Mn surrounded by four Mn vacancies.