Study on the Geometrically-frustrated Magnet Ni1/2Fe1/2Ga2S4

Abstract

We have investigated the spin-lattice relation in geometrical frustration by using an X-ray diffractometer (XRD), a superconducting quantum interference device (SQUID) magnetometer, and a Mossbauer spectroscopy. The crystal structure of the Ni1/2Fe1/2Ga2S4 studied here, was determined to be a 2-D triangular lattice structure of P-3m1 with lattice parameters of a(0) = 3.650 angstrom, and c(0) = 12.040 angstrom. From the temperature dependence of the molar susceptibility in an applied high field of H = 5 T measured by using a SQUID magnetometer, Ni1/2Fe1/2Ga2S4 had a strongly antiferromagnetic behavior due to the Curie-Weiss temperature theta(W) = -71.6 K. The freezing temperature at the onset of the spin-freezing transition was T-f = 10.0 K under a low field of H = 100 Oe, similar to a spin glass system, and the frustration parameter was f (vertical bar theta(W)vertical bar/T-N) = 3.25. From the Mossbauer spectrum at 4.2 K, we noticed a severely distorted 8-line shape coming from spin fluctuations and an incommensurate spin structure. The freezing temperature (T-f = 10 K) related to the electric spin disorder was different from the Neel temperature (T-N = 22 K) influenced by microscopic disorder of the nuclear spin due to a strained spin caused by the distorted lattice from geometrical frustration, as indicated in the Mossbauer spectra.