Low‐temperature magnetic properties of lepidocrocite

Abstract

The magnetic properties of synthetic lepidocrocite (γ‐FeOOH) were investigated between 5 and 300 K. The purity of the samples was verified by X‐ray diffraction and Mössbauer spectra at room temperature. The lepidocrocite is paramagnetic at room temperature with a low field susceptibility of 57.8 × 10−8 m3 kg−1. It undergoes magnetic ordering at low temperature and a peak in in‐phase susceptibility occurs around 52 K, where it is antiferromagnetic. Thermal demagnetization of low‐temperature remanence after cooling in zero field and in a 2.5‐T field display a large loss in remanence from 5 to 30 K. Hysteresis loops are open and symmetric about the origin below 50 K; the remanent magnetization probably arises from a defect magnetic moment. The field‐cooled hysteresis loop at 5 K is shifted along the field axis, which implies an exchange bias between antiferromagnetic and ferrimagnetic alignment in the lepidocrocite.