Incommensurate magnetism in the coupled spin tetrahedra system Cu2Te2O5Cl2

TL;DR

This study reveals complex incommensurate magnetic order and excitations in Cu2Te2O5Cl2, a tetrahedral spin system, highlighting geometrical frustration, anisotropic interactions, and multi-domain ground states.

Contribution

It provides detailed neutron scattering evidence of unconventional magnetism and spin arrangements in Cu2Te2O5Cl2, emphasizing the role of frustration and anisotropy in its magnetic properties.

Findings

Incommensurate magnetic order with wave vector ~[0.15, 0.42, 0.5].

Presence of two distinct spin excitation modes at 6.0 meV and 2 meV.

Magnetic domain redistribution under in-plane magnetic fields.

Abstract

Neutron scattering studies on powder and single crystals have provided new evidences for unconventional magnetism in Cu2Te2O5Cl2. The compound is built from tetrahedral clusters of S=1/2 Cu2+ spins located on a tetragonal lattice. Magnetic ordering, emerging at TN=18.2 K, leads to a very complex multi-domain, most likely degenerate, ground state, which is characterized by an incommensurate (ICM) wave vector k ~ [0.15, 0.42,1/2]. The Cu2+ ions carry a magnetic moment of 0.67(1) mB/ Cu2+ at 1.5 K and form a four helices spin arrangement with two canted pairs within the tetrahedra. A domain redistribution is observed when a magnetic field is applied in the tetragonal plane (Hc≈0.5 T), but not for H||c up to 4 T. The excitation spectrum is characterized by two well-defined modes, one completely dispersionless at 6.0 meV, the other strongly dispersing to a gap of 2 meV. The reason for such complex ground state and spin excitations may be geometrical frustration of the Cu2+ spins within the tetrahedra, intra- and inter-tetrahedral couplings having similar strengths and strong Dzyaloshinski-Moriya anisotropy. Candidates for the dominant intra- and inter-tetrahedral interactions are proposed.