Magnetic interaction at low temperature in chlorite and its products of oxidation; a Moessbauer investigation

Abstract

Three trioctahedral chlorites (Fe-clinochlore, Mn-Mgchamosite and Mg-chamosite) and their products of oxidation, an intersffatified chlorite-vermiculite for the clinochlore and vermiculite for chamosite, have been studied by s7p'a *-sbuuer spectroscopy at temperatures down to 1.3 K. Magnetic order is established inhomogeneously in a raqge of temperatures below 7 K. The Fd+ magnetichyperfine field is larger in clilorite than in vermiculite, and the range of N€el temperatures is lower in vermiculite. The results suggest that iron atoms are not uniformly distributed in octahedral sites of the hydroxide sheet and 2: I layer. A magnetic-hyperfine-field distribution at Fe2+ in chlorite, and at Fd+ and Fd+ in oxidized chlorite, indicates varying local environments around the iron nuclei. Comparison of the Mdssbauer spectra of chlorite and its products of oxidation, togetler with X-ray and chemical analyses, shows that even at 1.3 K there are magnetic and nonmagnetic domains in the hydroxide sheet and 2:1 layer of chlorite. The absence of long-range magnetic order in Mn-Mgchamosite at 1.6 K, inferred from neutron-diffraction data (Ballet er al. 1985a), is reinterpreted in terms of short correlation-lengths for magnetic order.