Magnetic properties and spin structure of MnO single crystal and powder

TL;DR

This study investigates the magnetic behavior of MnO, revealing that low-temperature peaks in magnetization are due to impurities at crystal interfaces rather than intrinsic properties.

Contribution

It provides new insights into the origin of low-temperature magnetic peaks in MnO, attributing them to impurities rather than the material's inherent spin structure.

Findings

Néel temperature confirmed at 118K for both forms

Low-temperature peak due to Mn2O3 or Mn3O4 impurities

Impurities grow at interfaces between MnO crystal twins

Abstract

Zero field cooled (ZFC)/Field Cooled (FC) magnetization curves of a bulk MnO single crystal show a peculiar peak at low temperatures (~40K) similar to the low temperature peak observed in MnO nanoparticles. In order to investigate the origin of this peak, the spin structure of a MnO single crystal has been studied and compared with a single phase powder sample using magnetometry and polarized neutron scattering. Both magnetometry and polarized neutron diffraction results confirm the antiferromagnetic (AF) phase transition at the N\'eel temperature T_N of 118K, in both powder and single crystal form. However, the low temperature peak in the ZFC/FC magnetization curves is not observed in single phase MnO powder. To better understand the observed behavior, ac susceptibility measurements have been employed. We conclude that the clear peak in the magnetic signal from the single crystal originates from a small amount of ferrimagnetic (FiM) Mn2O3 or Mn3O4 impurities, which is grown at the interfaces between MnO crystal twins.