EPR study of low spin domains formation in the process of spin transition in Na[Fe(Th-Sa)2

Abstract

The high spin (HS) $ low spin (LS) transition in a polycrystalline sodium salicylalthiosemicarbazonatoferrate(III) (Na[Fe(ThSa)2]) is studied by X-band EPR under atmospheric and hydrostatic pressure up to 600 MPa in the temperature range 80–330 K, when the effective value of the magnetic moment leff changes gradually from 5.9 down to 5.7 B.M. Its value diminishes rapidly below 50 K reaching 3.4 B.M. at 1.8 K. Some Q-band EPR measurements were performed in the range 150–236 K. The EPR linewidth analysis has shown that LS complexes formed are not statistically distributed among HS ones but aggregate in domains. In the gradual process of the HS ! LS transition, the EPR linewidth of the LS complexes reveals abrupt changes in two temperature ranges (240–236 and 195–191 K) related to rearrangement of complexes in domains. In the lower temperature range, the rearrangement is accompanied by a rapid increase in the LS complexes content. The application of external pressure stimulates the HS ! LS transition but the character of the process depends on temperature. An analysis of the process of the domain formation and destruction confirms the existence of the short- and long-range correlations between the LS complexes. � 2004 Elsevier B.V. All rights reserved.