FeMoO₄ revisited: Crosslike 90° noncollinear antiferromagnetic structure caused by dzyaloshinskii-moriya interaction

authored by

V. Ksenofontov, Yu G. Pashkevich, M. Panthöfer, V. Gnezdilov, R. Babkin, R. Klauer, P. Lemmens, A. Möller

Abstract

The ground state of Fe²⁺ (S = 2) in α- and β-FeMoO₄ is investigated by experiments including X-ray diffraction, Raman scattering, and ⁵⁷Fe-Mössbauer spectroscopy below 300 K and evaluated by theoretical modeling. Both modifications crystallize in the space group C2/m with the same set of Wyckoff positions. The structural feature of α- and β-FeMoO₄ is a tetramer of the so-called butterfly motif. Two iron-sites (Fe2) form an antiferromagnetically coupled dimer whereas two Fe1 establish an antiferromagnetic intertetramer coupling. The effective magnetic exchange of the two magnetic sublattices is based on dominating Dzyaloshinskii-Moriya interaction due to the rare situation of canceling Heisenberg exchange interactions. According to our investigations, the ground states of the two polymorphs differ in terms of their Fe-site specific electric field gradients V_ii. Contrary to the α-phase, a degenerate set of V_zz and V_yy for both iron sites in β-FeMoO₄ is extracted from density functional theory calculations. In the vicinity of the phase transition (β → α), the degeneracy of the β-phase is lifted. Correspondingly, we observe a softening of the ν(Mo-O) phonon modes. Detailed Mössbauer spectra confirm the crosslike 90° antiferromagnetic structure for both modifications and solve the origin of the longstanding issue of disparate quadrupole splittings in α- and β-FeMoO₄

External Organisation(s)

Johannes Gutenberg University Mainz
National Academy of Sciences in Ukraine
Technische Universität Braunschweig
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine

Type

Article

Journal

Journal of Physical Chemistry C

Volume

125

Pages

5947-5956

No. of pages

10

ISSN

1932-7447

Publication date

18.03.2021

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Energy(all), Physical and Theoretical Chemistry, Surfaces, Coatings and Films

Electronic version(s)

https://doi.org/10.1021/acs.jpcc.1c01134 (Access: Closed)