title: Softened magnetic excitations in the s = 3/2 distorted triangular antiferromagnet α-CaCr2O4.
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.
authors.affiliation: Institute for Condensed Matter Physics, Technical University of Braunschweig, Braunschweig, Germany. d.wulferding@tu-bs.de
authors.forename: Dirk
authors.initials: D
authors.lastname: Wulferding
authors.forename: Kwang-Yong
authors.initials: KY
authors.lastname: Choi
authors.forename: Peter
authors.initials: P
authors.lastname: Lemmens
authors.forename: Alexey N
authors.initials: AN
authors.lastname: Ponomaryov
authors.forename: Johan
authors.initials: J
authors.lastname: van Tol
authors.forename: A T M Nazmul
authors.initials: AT
authors.lastname: Islam
authors.forename: Sandor
authors.initials: S
authors.lastname: Toth
authors.forename: Bella
authors.initials: B
authors.lastname: Lake