Dielectric, magnetic, and magnetodielectric behaviors of BaFe12O19 hexaferrite modulated by Mn and Ti substitutions

TL;DR

This study investigates how Mn and Ti doping in BaFe12O19 hexaferrite alters its magnetic, dielectric, and magnetodielectric properties, revealing site-specific effects and potential for property modulation.

Contribution

It provides detailed insights into site-specific doping effects on the physical properties of BaFe12O19, including spin order stabilization and dielectric behavior, expanding understanding of hexaferrite modulation.

Findings

Ti doping stabilizes noncollinear spin order up to room temperature.

Mn-Ti co-doping enhances low-field magnetodielectric responses.

Dielectric response is dominated by electron hopping and interfacial polarization at different temperatures.

Abstract

We prepared Mn- and Ti mono-doped and co-doped BaFe12O19 hexaferrites via solid-state reaction. Mn ions preferentially occupy the 4f2 and 2b sites, while Ti ions mainly substitute the Fe3+ ions at 4f1 and 12k sites as revealed by the Raman spectroscopy and formation energy. Pure BaFe12O19 exhibits ferrimagnetism. The hexaferrites related to Ti doping have noncollinear longitudinal conical spin order at low temperatures, where BaFe6Mn3Ti3O19 retains this spin order up to room temperature. Ti4+ substitution at 4f1 and 12k sites plays a pivotal role in stabilizing the noncollinear conical spin order through adjusting the superexchange interactions and reducing the uniaxial magnetocrystalline anisotropy along the c-axis. The magnetic response exhibits two distinct transition temperatures because Ti4+ ions interrupt the magnetic superexchange interactions with two inequivalent exchange integrals. Pure BaFe12O19 presents a quantum paraelectric behavior at low temperatures, which is disrupted by Mn-Ti doping due to the decoupling of electric dipoles within the triangular bipyramid. Electron hopping and polaronic effects dominate the dielectric response at 10 - 50 K, while Maxwell-Wagner interfacial polarization and electron hopping contribute to dielectric dispersion at higher temperatures. The negative MD effect of pure BaFe12O19 and BaFe6Mn3Ti3O19 at 10 K originates from spin-phonon coupling and electric polarization induced by noncollinear spin order under magnetic field, respectively. The Mn-Ti co-doped samples achieve relatively higher MD responses at low magnetic fields. In higher temperatures, the MD effect arises mainly from the magnetic field modulation of the electron hopping with non-intrinsic interfacial polarization. This research reveals the physical properties of M-type hexaferrite can be modulated through substituting Fe3+ ions at different sites.