Magnetic and Optical Properties of the High- and Low-Pressure Forms of CsCoF3

Abstract

CsCoF3 has hcp (h) and ccp (c) CsF3 layers alternating hhchhchhc at atmospheric pressure (9L structure of BaRuO3) but a cchcch sequence (6L structure of RbNiF3) if quenched from 700°C at pressures greater than 20 kbar. The octahedral-site Co2+ ions are between the layers and give the 9L structure a pink color, the 6L structure a lavender hue. The 9L phase obeys a Curie-Weiss law above 70°K with Cm=3.7 emu°K/mole and Θp=−62°K. It has TN=8°K with evidence for a spin-flop transition at Hc≈11 kOe and an anisotropy constant K≈5×104 ergs/cm3 at 4.2°K. The 6L phase has Cm=3.3 emu°K/mole, Θp=−65°K and is ferrimagnetic below TC=50°K. The magnetization is not saturated at 17.2 kOe and 4.2°K, where μ̄=0.8 μB/Co2+ is smaller than the 1.23 μB/Co2+ anticipated at saturation for RbNiF3-type ordering. Optical data show a larger trigonal-field splitting for the 6L structure. For both phases, Dq≈760 cm−1, spin-orbit interaction parameter ζ≈500 cm−1, and long wavelength cutoff≈13 μm.