The linear electrochromic effect in meta-nitroaniline : J.L. Stevenson, S. Ayers and M.M. Faktor, Post Office Research Department, Dollis Hill, London NW2 7DT

Abstract

Bulk and local magnetic properties of the polycrystalline Fe2MnGa compound, submitted to cold-work and annealing, have been studied using DC magnetization measurements and 57Fe Mössbauer spectroscopy in a broad temperature range (15–400 K). Structural characterization has shown stabilization of an ordered L12-type structure for annealed materials. Mechanical cold-work induces grain refinement and internal stress enhancement in the L12-type structure, favoring antisite disorder. The chemical disorder favors competitions between antiferro and ferromagnetic interactions and, consequently, leading to a frustrated magnetic state when Fe and Mn sublattices ordered magnetically. Due to the chemical disorder intrinsically found in as-prepared sample or enhanced in annealed cold-work materials, we have shown (i) metamagnetic transition from antiparallel Fe and Mn coupling to a non-collinear magnetic state when applied field strength is increased and (ii) a wasp-waisted magnetic loop character (measured in annealed materials) as consequence of frustration in magnetic interactions between misplaced Fe and Mn neighbors. We also demonstrated that even under similar experimental annealing conditions, the chemical disorders in as-prepared, ribbon and powder samples of the same batch are different, producing distinct magnetic properties of the final product.