Softened magnetic excitations in the s = 3/2 distorted triangular antiferromagnet α-CaCr2O4

J Phys Condens Matter. 2012 Oct 31;24(43):435604. doi: 10.1088/0953-8984/24/43/435604. Epub 2012 Oct 8.

Abstract

The spin dynamics and magnetic excitations of the slightly distorted triangular s = 3/2 system α-CaCr (2)O (4) are investigated by means of Raman spectroscopy and electron spin resonance (ESR) to elucidate its peculiar magnetic properties. Two-magnon excitations in circular RL symmetry show a multi-maximum structure with a dominant spectral weight at low energies. The temperature dependence of the ESR linewidth is described by a critical broadening ΔH(pp)(T) is proportional to (T-T(N ))(-p) with the exponent p = 0.38(5) - 0.48(3) for temperatures above T(N) = 42.6 K. The exponent is much smaller than that of other s = 3/2 triangular lattices. This is ascribed to soft roton-like modes, indicative of the instability of a helical 120° phase. As an origin we discuss a complex spin topology formed by four inequivalent nearest neighbor and sizable next-nearest neighbor interactions.

Publication types

  • Research Support, Non-U.S. Gov't