Mössbauer effect study of iron borate Fe2+2Fe3+(BO3)O2 with hulsite structure

Abstract

The room temperature Fe Mossbauer spectrum of hulsite was processed by sum of three components, namely, one magnetically splitted component and two paramagnetic doublets. Tliis fact means a partial magnetic ordering of iron atoms in the hulsite. It should be caused by two-dimensional character of magnetic interaction. Hyperfine parameters of magnetically splitted component are characteristic for ferric ions, while the parameters of other components - for ferrous ions. With an increasing of temperature, hyperfine field of magnetically splitted component decreases, and magnetic splitting disappears at about 383 K. At the temperatures above 600 K, new magnetically splitted component appears. This component is related with hematite (а-РезОз), and its appearance is connected with the start of oxidation of the hulsite.