Wulferding, D.; Choi, K.-Y.; Lemmens, P.; Ponomaryov, A.N.; van Tol, J.; Islam, A.T.M.N.; Toth, S.; Lake, B.: Softened magnetic excitations in the s=3/2 distorted triangular antiferromagnet alpha-CaCr2O4. Journal of Physics: Condensed Matter 24 (2012), p. 435604/1-7
10.1088/0953-8984/24/43/435604
Open Access Version (externer Anbieter)
Abstract:
Abstract The spin dynamics and magnetic excitations of the slightly distorted triangular s D 3=2 system -CaCr2O4 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 1Hpp.T/ / .T TN/p with the exponent p D 0:38.5/ 0:48.3/ for temperatures above TN D 42:6 K. The exponent is much smaller than that of other s D 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. (Some figures may appear in colour only in the online journal)