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arXiv · 2101.06786

Experimental determination of the magnetic interactions of frustrated Cairo pentagon lattice materials

Manh Duc Le·Elisa M. Wheeler·Jaehong Jeong·K. Ramesh Kumar·Seongsu Lee·Chang-Hee Lee·Myeong Jun Oh·Youn-Jung Jo·Akihiro Kondo·Koichi Kindo·U. Stuhr·B. Fåk·M. Enderle·Dmitry Batuk·Artem M. Abakumov·Alexander A. Tsirlin·Je-Geun Park
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Abstract

We present inelastic neutron scattering measurements of the Cairo pentagon lattice magnets Bi$_2$Fe$_4$O$_9$ and Bi$_4$Fe$_5$O$_{13}$F, supported by high field magnetisation measurements of Bi$_2$Fe$_4$O$_9$. Using linear spin wave theory and mean field analyses we determine the spin exchange interactions and single-ion anisotropy in these materials. The Cairo lattice is geometrically frustrated and consists of two inequivalent magnetic sites, both occupied by Fe$^{3+}$ ions and connected by two competing nearest neighbour interactions. We found that one of these interactions, coupling nearest neighbour spins on the three-fold symmetric sites, is extremely strong and antiferromagnetic. These strongly coupled dimers are then weakly coupled to a framework formed from spins occupying the other inequivalent site. In addition we found that the Fe$^{3+}$ $S=5/2$ spins have a non-negligible single-ion anisotropy, which manifests as a spin anisotropy gap in the neutron spectrum and a spin-flop transition in high field magnetisation measurements.

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Manh Duc Le, Elisa M. Wheeler, Jaehong Jeong, K. Ramesh Kumar, Seongsu Lee, Chang-Hee Lee, Myeong Jun Oh, Youn-Jung Jo, Akihiro Kondo, Koichi Kindo, U. Stuhr, B. Fåk, M. Enderle, Dmitry Batuk, Artem M. Abakumov, Alexander A. Tsirlin, Je-Geun Park. 2021-01-17. Experimental determination of the magnetic interactions of frustrated Cairo pentagon lattice materials. https://doi.org/10.1103/physrevb.103.104423

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