Magnetic and electrical properties of ilvaite

Abstract

Electrical conductivity, magnetization, magnetic susceptibility, and Mössbauer spectra are reported for three samples of ilvaite, a mixed-valence iron silicate with ideal composition CaFe2+2Fe3+Si2O8(OH). The Néel temperature is 118±3 K, but there is evidence from the susceptibility for competing antiferromagnetic and ferromagnetic exchange interactions. Analysis of the Mössbauer spectra at 4.2 K for Fe2+ at A and B sites, shows that e2qQ is positive and η∼0, indicating pseudotetragonal local symmetry and orbital singlet ground states for both ions. A peak found at 40 K in the susceptibility measured with the field perpendicular to the c axis may be related to the temperature dependence of the Fe2+ single-ion anisotropy.