Magnetic structure determination from the magnetic pair distribution function (mPDF): ground state of MnO

TL;DR

This study demonstrates the use of magnetic pair distribution function analysis to determine the ground-state magnetic and atomic structure of MnO, revealing local monoclinic order despite an average rhombohedral structure.

Contribution

First experimental application of mPDF to MnO, showing local monoclinic structure and magnetic configuration consistent with known antiferromagnetic order.

Findings

Local monoclinic structure identified via mPDF

Magnetic moments aligned along [10̅1] direction

Local structure extends up to ~100 Å

Abstract

An experimental determination of the magnetic pair distribution function (mPDF) defined in an earlier paper (Frandsen, Yang, and Billinge. (2014) Acta Crystallogr. A, 70(1), 3-11) is presented for the first time. The mPDF was determined from neutron powder diffraction data from a reactor and a neutron time-of-flight total scattering source on a powder sample of the antiferromagnetic oxide MnO. A description of the data treatment that allowed the measured mPDF to be extracted and then modelled is provided and utilized to investigate the low-temperature structure of MnO. Atomic and magnetic co-refinements support the scenario of a locally monoclinic ground-state atomic structure, despite the average structure being rhombohedral, with the magnetic PDF analysis successfully recovering the known antiferromagnetic spin configuration. The total scattering data suggest a preference for the spin axis to lie along the pseudocubic [10$\bar{1}$] direction. Finally, $r$-dependent PDF refinements indicate that the local monoclinic structure tends toward the average rhombohedral $R\overline{3}m$ symmetry over a length scale of approximately 100~\AA.