Rotomagnetic couplings influence on the magnetic properties of antiferrodistortive antiferromagnets

TL;DR

This study uses Landau-Ginzburg-Devonshire theory to show how rotomagnetic couplings significantly affect the magnetic and dielectric properties of antiferrodistortive antiferromagnets like EuTiO3, enabling control via external fields.

Contribution

It demonstrates the strong influence of rotomagnetic coupling on magnetic transition temperatures and phase behavior, introducing a new way to control multiferroic properties.

Findings

Rotomagnetic coupling determines the Néel temperature in EuTiO3.

The order of the antiferromagnetic phase transition depends on the coupling strength.

External electric fields can induce phase transitions at lower thresholds due to rotomagnetic effects.

Abstract

Within the framework of Landau-Ginzburg-Devonshire (LGD) phenomenological theory we consider the possibility to control properties of paraelectric antiferromagnets via biquadratic rotomagnetic coupling with and without external magnetic and electric field application. We use EuTiO3 as a prototype with relatively well-known material parameters. Surprisingly strong influence of this coupling practically on all the properties without external fields was obtained in the temperature region with coexistence of antiferromagnetic and antiferrodistorted phases i.e. in multiferroic state. In particular, the observed Neel temperature TN (5.5 K) was shown to be defined by rotomagnetic coupling, while without this coupling TN appeared to be much higher (26 K). For small or high enough rotomagnetic coupling constant value the antiferromagnetic phase transition order appeared to be the second or the first order respectively. The essential influence of rotomagnetic coupling on the form and value of magnetic and dielectric permittivity was also forecasted. The rotomagnetic coupling along with rotoelectric one opens the additional way to control the form of the phase diagrams by application of external magnetic or electric field. The critical value of the electric field (for antiferromagnetic to ferromagnetic phase transition) appeared essentially smaller than the one calculated without rotomagnetic coupling that can be important for applications.