Contrasting magnetoelectric behavior in multiferroic hexaferrites as understood by crystal symmetry analyses

TL;DR

This study compares the magnetoelectric behavior of two hexaferrites, revealing how crystal symmetry influences their different responses and microscopic mechanisms, advancing understanding of giant ME coupling in multiferroic materials.

Contribution

It provides a symmetry-based analysis explaining contrasting ME behaviors and microscopic origins in two similar hexaferrites, highlighting the role of crystal symmetry.

Findings

Opposite rotation directions of P vector in the two hexaferrites.

Symmetry analysis links P rotation to mirror plane presence.

Different microscopic mechanisms (inverse DM vs p-d hybridization) are identified.

Abstract

Magnetoelectric (ME) properties under rotating magnetic field H are comparatively investigated in two representative hexaferrites Y-type Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 and Z-type Ba0.52Sr2.48Co2Fe24O41, both of which have exhibited a similar transverse conical spin structure and giant ME coupling near room temperature. When the external H is rotated clockwise by 2pi, in-plane P vector is rotated clockwise by 2pi in the Y-type hexaferrite and counterclockwise by 4pi in the Z-type hexaferrite. A symmetry-based analysis reveals that the faster and opposite rotation of P vector in the Z-type hexaferrite is associated with the existence of a mirror plane perpendicular to c-axis. Moreover, such a peculiar crystal symmetry also results in contrasting microscopic origins for the spin-driven ferroelectricity; only the inverse DM interaction is responsible for the Y-type hexaferrite while additional p-d hybridization becomes more important in the Z-type hexaferrite. This work demonstrates the importance of the crystal symmetry in the determination of ME properties in the hexaferrites and provides a fundamental framework for understanding and applying the giant ME coupling in various ferrites with hexagonal crystal structure.