Rethinking the Magnetic Properties of Lepidocrocite: A Density Functional Theory and Cluster Expansion Study

The iron oxyhydroxide lepidocrocite (γ-FeOOH) is an abundant mineral critical to a number of chemical and technological applications. Of particular interest is the ground state and finite temperature magnetic order, and the subsequent impact this has upon crystal properties. The magnetic properties, investigated in this work are governed primarily through superexchange interactions, and have been calculated using density functional theory and cluster expansion methods. Quantification of these exchange terms has facilitated the determination of the ground state magneto-crystalline structure and subsequent calculation of its lattice constants, elastic moduli, cohesive enthalpy, and electronic density of states. Further, using a collinear magnetic configuration model, the magnetic heat capacity versus temperature has been studied and the N ́eel temperature obtained.