Surface-dependent magnetic behavior of α-Fe2O3 quasi-cubes induced by Mg2+ ions

Abstract

Uniform α-Fe₂O₃ quasi-cubes with high-index facets exposed were synthesized in a controlled manner through a simple hydrothermal method using Mg²⁺ ions as structure-directing agents. The as-prepared α-Fe₂O₃ quasi-cubes are bound by (012), (10−2), and (1−12) facets with an edge length of about 200 nm and a dihedral angle of 86°. In the reaction system, the Mg²⁺ ions would undertake the role of structure and surface director, adsorb to the α-Fe₂O₃ high energy surface and induce the α-Fe₂O₃ nanoparticles to grow into quasi-cubic nanocrystals bound by high-index facets. Magnetic measurements testify that the quasi-cubes display surface-dependent magnetic behavior. The α-Fe₂O₃ quasi-cubes have a splitting between the FC curve and the ZFC curve from the highest experimental temperature to the lowest temperature and no Morin transformation occurs, indicating that they would be under defect ferromagnetic control both at room temperature and low temperature.