Magnetic states of coupled spin tubes with frustrated geometry in CsCrF4

When a theoretical model is realized in nature, small perturbation terms play important roles in the selection of the ground state in geometrically frustrated magnets. In case of a triangular spin tube, the two-dimensional network of the inter-tube interaction forms characteristic lattices. Among them Kagome-Triangular (KT) lattice is known to exhibit an enriched phase diagram including various types of non-trivial structures: non-coplanar cuboc structure, coplanar 120° structure with the two-dimensional propagation vector of \({\boldsymbol{k}}_{2\mathrm{D}}\)？=？(0, 0), \(\sqrt 3 \times \sqrt 3\) structure with \({\boldsymbol{k}}_{2{\mathrm{D}}}\)？=？(1/3, 1/3), and incommensurate structure. We investigate the magnetic state in the model material CsCrF4 by using neutron diffraction technique. Combination of representation analysis and Rietveld refinement reveals that a very rare structure, i.e., a quasi-120° structure with \({\boldsymbol{k}}_{2{\mathrm{D}}}\)？=？(1/2, 0), is realized at the base temperature. The classical calculation of the phase diagram elucidates that CsCrF4 is the first experimental realization of the KT lattice having ferromagnetic Kagome bond. A single-ion anisotropy and Dzyaloshinskii-Moriya interaction play key roles in the selection of the ground state. Furthermore, a successive phase transition having an intermediate state represented by \({\boldsymbol{k}}_{2{\mathrm{D}}}\)？=？(1/3, 1/3) is observed. The intermediate state is a partially ordered 120° structure which is induced by thermal fluctuation