Terahertz frequency magnetoelectric effect in Ni doped CaBaCo$_4$O$_7$

TL;DR

This study investigates the terahertz magnetoelectric effect in Ni-doped CaBaCo$_4$O$_7$, revealing magnetic field modulation of phonons and providing data for theoretical modeling of magnetoelectricity.

Contribution

It reports the terahertz magnetoelectric response in Ni-doped CaBaCo$_4$O$_7$ and analyzes phonon contributions using the Lorentz model, advancing understanding of magnetoelectric mechanisms.

Findings

Magnetic field modulates infrared-active phonons near 1.2 and 1.6 THz.

Optical phonons near 1.6 THz significantly contribute to the magnetoelectric effect.

Results support development of detailed theoretical models of magnetoelectricity.

Abstract

We present a study of terahertz frequency magnetoelectric effect in ferrimagnetic pyroelectric CaBaCo$_4$O$_7$ and its Ni-doped variants. The terahertz absorption spectrum of these materials consists of spin excitations and low-frequency infrared-active phonons. We studied the magnetic-field-induced changes in the terahertz refractive index and absorption in magnetic fields up to 17 T. We find that the magnetic field modulates the strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the Lorentz model of the dielectric function to analyze the measured magnetic-field dependence of the refractive index and absorption. We propose that most of the magnetoelectric effect is contributed by the optical phonons near 1.6 THz and higher-frequency resonances. Our experimental results can be used to construct and validate more detailed theoretical descriptions of magnetoelectricity in CaBaCo$_{4-x}$Ni$_x$O$_7$.