Statics and dynamics of an incommensurate spin order in a geometrically frustrated antiferromagnet CdCr$_2$O$_4$

TL;DR

This study reveals the incommensurate spin order and magnetic excitations in CdCr₂O₄, a geometrically frustrated antiferromagnet, showing unique structural and magnetic phase transitions distinct from similar compounds.

Contribution

It provides detailed neutron scattering analysis of the incommensurate spin structure and magnetic excitations in CdCr₂O₄, highlighting its unique phase transition behavior.

Findings

CdCr₂O₄ undergoes a spin-Peierls-like transition at 7.8 K with elongation along the c-axis.

The Néel phase exhibits an incommensurate spin structure with wave vector (0, δ, 1).

Magnetic excitations include a weak anisotropy gap of 0.6 meV and three energy bands up to 5 meV.

Abstract

Using elastic and inelastic neutron scattering we show that a cubic spinel, CdCr$_2$O$_4$, undergoes an elongation along the c-axis ($c > a = b$) at its spin-Peierls-like phase transition at $T_N$ = 7.8 K. The N\'{e}el phase ($T < T_N$) has an incommesurate spin structure with a characteristic wave vector \textbf{Q}$_M$ = (0,$\delta$,1) with $\delta \sim$ 0.09 and with spins lying on the $ac$-plane. This is in stark contrast to another well-known Cr-based spinel, ZnCr$_2$O$_4$, that undergoes a c-axis contraction and a commensurate spin order. The magnetic excitations of the incommensurate N\'{e}el state has a weak anisotropy gap of 0.6 meV and it consists of at least three bands extending up to 5 meV.