Helical magnetic state in the distorted triangular lattice of alpha-CaCr2O4

TL;DR

This study investigates the magnetic properties of alpha-CaCr2O4, revealing a unique incommensurate helical magnetic phase at 43K with implications for magnetoelectric effects.

Contribution

First detailed investigation of magnetic behavior in alpha-CaCr2O4, identifying a novel helical magnetic phase and analyzing its symmetry and magnetoelectric properties.

Findings

Magnetic phase transition at 43K to incommensurate helical order

Magnetic propagation vector k=(0,0.3317,0)

Magnetic point group predicts quadratic magnetoelectric effects

Abstract

The magnetic properties of the high temperature alpha form of the CaCr2O4 compound have been investigated for the first time by magnetic susceptibility, specific heat and powder neutron diffraction. The system undergoes a unique magnetic phase transition at 43K to a long range order incommensurate helical phase with magnetic propagation vector k=(0,0.3317(2),0). The magnetic model proposed from neutron diffraction data shows that the plane of rotation of the spins is perpendicular to the wave-vector, and that the magnetic modulation is consistent with two modes belonging to distinct irreducible representations of the group. The magnetic point group 2221' is not compatible with ferroelectricity unlike the CuCrO2 delafossite [Kimura et al., Phys. Rev. B, 78 140401 (2008)] but predicts the existence of quadratic magnetoelectric effects, discussed based on a Landau analysis.