Polar modes in multiferroic Ba_2Mg_2Fe_(12)O_(22) hexagonal Y-type hexaferrite

TL;DR

This study investigates the vibrational and magnetic excitations in a multiferroic hexaferrite using Terahertz and infrared spectroscopy across a range of temperatures, revealing new magnetic excitations linked to phase transitions.

Contribution

It provides detailed spectral analysis of Ba_2Mg_2Fe_12O_22, identifying new magnetic excitations associated with phase transitions, advancing understanding of multiferroic hexaferrites.

Findings

Identification of 19 phonon modes consistent with crystal symmetry

Discovery of new absorption lines below phase transition temperatures

Assignment of these lines to electric-dipole active magnetic excitations

Abstract

Spectra of transmission and reflection coefficients of single crystalline Y-type hexaferrite Ba_(2)Mg_(2)Fe_(12)O_(22) are measured at Terahertz and infrared frequencies, 3 - 4500 c--1, and at temperatures 10 to 300 K, for polarization E prp c. Oscillator parameters of nineteen phonon lines allowed by the R3m crystal lattice symmetry are determined. Absorption lines assignment to vibrational modes of the lattice structural fragments is performed. Below the temperatures of 195 K and 50 K, corresponding to the zero field phase transitions to the proper screw and to the longitudinal-conical spin states, respectively, new absorption lines are discovered whose origin is assigned to the electric-dipole active magnetic excitations.