Incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl, Br) studied by single crystal neutron diffraction

TL;DR

This study investigates the incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl, Br) using neutron diffraction, revealing a common canted coplanar spin structure with different magnetic moments and propagation vectors.

Contribution

The paper presents the first detailed magnetic structure models for Cu2Te2O5X2 (X=Cl, Br) based on neutron diffraction, highlighting incommensurate ordering and a helix-like spin arrangement.

Findings

Identified incommensurate propagation vectors for X=Cl and X=Br.

Determined magnetic moments: 0.88μB for Cl and 0.395μB for Br.

Proposed a canted coplanar spin structure with helix rotation.

Abstract

Polarized and unpolarized neutron diffraction studies have been carried out on single crystals of the coupled spin tetrahedra systems Cu2Te2O5X2 (X=Cl, Br). A model of the magnetic structure associated with the propagation vectors k'Cl ~ -0.150,0.422,1/2 and k'Br ~ -0.172,0.356,1/2 and stable below TN=18 K for X=Cl and TN=11 K for X=Br is proposed. A feature of the model, common to both the bromide and chloride, is a canted coplanar motif for the 4 Cu2+ spins on each tetrahedron which rotates on a helix from cell to cell following the propagation vector. The Cu2+magnetic moment determined for X=Br, 0.395(5)muB, is significantly less than for X=Cl, 0.88(1)muB at 2K. The magnetic structure of the chloride associated with the wave-vector k' differs from that determined previously for the wave vector k~0.150,0.422,1/2 [O. Zaharko et.al. Phys. Rev. Lett. 93, 217206 (2004)].