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arXiv · 2009.03666

Structural dimerization in the commensurate magnetic phases of NaFe(WO$_4$)$_2$ and MnWO$_4$

S. Biesenkamp·N. Qureshi·Y. Sidis·P. Becker·L. Bohatý·M. Braden
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Abstract

The structural distortion and magnetoelastic coupling induced through commensurate magnetism has been investigated by neutron diffraction in structurally related MnWO$_4$ and NaFe(WO$_4$)$_2$. Both systems exhibit a competition of incommensurate spiral and commensurate spin up-up-down-down ordering along the magnetic chains. In the latter commensurate phases, the alternatingly parallel and antiparallel arrangement of Fe$^{3+}$ respectively Mn$^{2+}$ moments leads to sizeable bond-angle modulation and thus to magnetic dimerization. For NaFe(WO$_4$)$_2$ this structural distortion has been determined to be strongest for the low-field up-up-down-down arrangement, and the structural refinement yields a bond-angle modulation of $\pm 1.15(16)$ degrees. In the commensurate phase of MnWO$_4$, superstructure reflections signal a comparable structural dimerization and thus strong magneto-elastic coupling different to that driving the multiferroic order. Pronounced anharmonic second- and third-order reflections in the incommensurate and multiferroic phase of MnWO$_4$ result from tiny commensurate fractions that can depin multiferroic domains.

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S. Biesenkamp, N. Qureshi, Y. Sidis, P. Becker, L. Bohatý, M. Braden. 2020-09-08. Structural dimerization in the commensurate magnetic phases of NaFe(WO$_4$)$_2$ and MnWO$_4$. https://doi.org/10.1103/physrevb.102.144429

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