The crystal and magnetic structures of the $S=\frac{3}{2}$ antiferromagnet $\beta {\text{-CaCr}}_2{\text{O}}_4$ have been investigated by means of specific heat, magnetization, muon relaxation, and neutron powder diffraction between 300 and 1.5 K. In this compound, in which the unusual topology of the ${\text{Cr}}^{3+}$ magnetic lattice can be described as a network of triangular “zigzag” ladders with legs parallel to $c$, a complex antiferromagnetic ordering with an incommensurate propagation vector $\mathbf{k}=\left(0,0,q\right)$ ($q\sim 0.477$ at 1.5 K) is evidenced below $T_{\text{N}}=21\text{K}$. This complex magnetic ordering can be described as a honeycomblike arrangement of cycloids, running along $c$, and presenting a unique pattern of staggered chirality. To understand the experimental observation of this staggered chirality, we propose to use antisymmetric Dzyaloshinskii-Moriya terms in the exchange Hamiltonian.

• Received 12 June 2009

DOI:https://doi.org/10.1103/PhysRevB.81.214405