Temperature-dependent properties of the magnetic order in single-crystal BiFeO3

TL;DR

This study investigates how the magnetic order in single-crystal BiFeO3 varies with temperature, revealing details about magnetic domains, cycloid behavior, and implications for electromagnon understanding.

Contribution

It provides detailed temperature-dependent neutron diffraction and magnetization data on BiFeO3's magnetic cycloids, clarifying previous conflicting reports and highlighting the role of anharmonicity.

Findings

Magnetic cycloid period increases with temperature.

Magnetic domain populations remain stable except near Néel temperature.

Cycloid is nearly circular at room temperature.

Abstract

We report neutron diffraction and magnetization studies of the magnetic order in multiferroic BiFeO3. In ferroelectric monodomain single crystals, there are three magnetic cycloidal domains with propagation vectors equivalent by crystallographic symmetry. The cycloid period slowly grows with increasing temperature. The magnetic domain populations do not change with temperature except in the close vicinity of the N{\P}eel temperature, at which, in addition, a small jump in magneti- zation is observed. No evidence for the spin-reorientation transitions proposed in previous Raman and dielectric studies is found. The magnetic cycloid is slightly anharmonic for T=5 K. The an- harmonicity is much smaller than previously reported in NMR studies. At room temperature, a circular cycloid is observed, within errors. We argue that the observed anharmonicity provides important clues for understanding electromagnons in BiFeO3.