Insights into the Structural and Microscopic Origin of Magnetic Properties of the γ-Fe2O3@MnxOy Nanostructure

Abstract

Hetero-nanostructures having multi-layered ferromagnetic–antiferromagnetic ultrathin films, dispersion of ferromagnetic particles to the antiferromagnetic matrix, and a core–shell model (F@AF) can exhibit an exchange bias (HEB) that will be useful for spintronic materials such as spin valves, magnetic random-access memories, and ultrahigh data storage. The spin proximity effect of F and AF in the monodispersed core–shell is not much reported. For the first time, we report the preparation of core–shell monodispersed nanoparticles of γ-Fe2O3@MnxOy having different thicknesses of shells. The microscopic origin of magnetic properties and the microscopic crystal structure are explained by experimental results such as energy-dispersive analysis of X-rays line scanning, X-ray absorption near-edge spectroscopy, and magnetic data. The values of HEB for γ-Fe2O3@MnxOy (Mn6) and γ-Fe2O3@MnxOy (Mn12) are found to be 8 and 79 Oe, respectively. Also, possible theoretical models such as crystal field stabilization energy for normal or inverse spinel structures and possible magnetic proximity interactions in core@shell models are discussed. Interestingly, samples show the heating behavior required for hyperthermia under an AC magnetic field, and materials will be potential for hyperthermia cancer therapy. Thermal decomposition of γ-Fe2O3@MnxOy produces α-Fe2–2xMn2xO3 at 550 °C, but their unit cell volumes are almost the same even after occupancy of 12 at. % Mn3+ in Fe3+ sites, and the origin of this behavior is explained for the first time.