Abstract
The spin dynamics and magnetic excitations of the slightly distorted triangular s = 3/2 system α-CaCr 2O 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 ΔHpp(T) ∝ (T−TN )−p with the exponent p = 0.38(5) − 0.48(3) for temperatures above TN = 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.
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