Controlling Degree of Inversion in MgFe₂O₄ Spinel Films Grown in External Magnetic Fields

Single-phase magnesium ferrite spinel films (MgFe2O4) were grown by magnetic field-assisted chemical vapor deposition (mfCVD) of a mixed-metal precursor compound, [MgFe2((OBu)-Bu-t)(8)]. The formation of monophasic MgFe2O4 deposits as a function of the applied magnetic field strength (B = 0.0, 0.5, and 1.0 T) was investigated and confirmed by X-ray diffraction and photoelectron spectroscopy analyses. Thin film cross-sectional electron microscopic analysis (FIB-SEM) exhibited higher grain growth and densification in MgFe2O4 films obtained under the magnetic field influence when compared to spinel samples grown under zero-field conditions. Application of an external magnetic field of varying strengths during the chemical vapor deposition process resulted in a change in the light absorption properties and crystal orientation in the MgFe2O4 films, evident in the decreased photoabsorbance analyzed by the UV-Vis spectra and the decrease of intensity of the (400) peak in MgFe2O4 films grown under magnetic field. A comprehensive analysis of X-ray diffraction and X-ray magnetic circular dichroism (XMCD) results indicated a higher degree of inversion in MgFe2O4 deposits grown in an external magnetic field corroborated by a larger contribution of ligand field transitions of tetrahedrally coordinated Fe(III) centers affecting the visible light absorption of MgFe2O4 films.