Magnetism of iron pyrite (FeS2) — a Mössbauer study in an external magnetic field

The Mössbauer effect in the presence of external fields up to 36 kOe has been used to show the absence of a magnetic moment at the iron atom in FeS₂. The electric field gradient at the iron nucleus was found to be negative.     

Spin moment over 10-300 K and delocalization of magnetic electrons above the Verwey transition in magnetite

In order to probe the magnetic ground state, we have carried out temperature-dependent magnetic Compton scattering experiments on an oriented single crystal of magnetite (Fe₃O₄), together with the corresponding first-principles band theory computations to gain insight into the measurements. An accurate value of the magnetic moment μ_S associated with unpaired spins is obtained directly over the temperature range of 10-300 K. μ_S is found to be non-integral and to display an anomalous behavior with the direction of the external magnetic field near the Verwey transition. These results reveal how the magnetic properties enter the Verwey energy scale via spin-orbit coupling and the geometrical frustration of the spinel structure, even though the Curie temperature of magnetite is in excess of 800 K. The anisotropy of the magnetic Compton profiles increases through the Verwey temperature T_v and indicates that magnetic electrons in the ground state of magnetite become delocalized on Fe B-sites above T_v.