Electronic structure, and dielectric, magnetic and reflection-loss behaviors of BaFe12-xMnxO19 (0 < x ≤ 2) hexaferrites

Abstract

M−type hexaferrites doped with transition metals are important materials used widely in modern electronic devices. Although many research works considered their magnetic properties, the relation between their electronic structure and electromagnetic behaviors have been less taken into account, particularly Mn-doped M−type hexaferrites. This work presents a detailed study on the electronic structure, and dielectric, magnetic and reflection-loss behaviors of BaFe12-xMnxO19 (x = 0.5, 1 and 2) hexaferrite specimens prepared by conventional solid-state reactions. The analysis of X-ray absorption spectra proves a mixed oxidation state of Fe2+,3+ and Mn2+,3+ ions, and chemical shifts of Fe2+ → Fe3+ and Mn2+ → Mn3+ when x increases from 0.5 to 2. These factors change the unit-cell volume, and cause Mn3+-related Jahn-Teller distortions. Concurrently, the saturation magnetization Ms varies in the range from 24 to ∼31 emu/g, which is associated with interaction competitions between Fe2+,3+-Mn2+,3+ pairs and Fe2+-related spin canting. Having studied electromagnetic behaviors, we have found strong changes in values of the permittivity and permeability at frequencies f = 10∼15 GHz. For a thickness t = 2.4 mm, reflection-loss magnitudes of microwave are about 10 ∼ 11 dB (corresponding to above 90% microwave being absorbed), with an absorption bandwidth of ∼3 GHz. Assessments of the magnetic and dielectric loss tangents, and Cole-Cole curves indicate electrical energy dissipation associated with interfacial/dipolar polarizations and conductive loss playing a dominant role in microwave absorption of BaFe12-xMnxO19.