Magnetic phase diagram of the multiferroic FeTe$_2$O$_5$Br

TL;DR

This study maps the magnetic phase diagram of multiferroic FeTe$_2$O$_5$Br at low temperatures and high magnetic fields, revealing complex phase transitions and the influence of magnetic field orientation on magnetic and electric properties.

Contribution

It provides the first detailed magnetic phase diagram of FeTe$_2$O$_5$Br down to 300 mK and up to 9 T, highlighting the field-dependent phase transitions and their relation to magnetic correlations.

Findings

Short-range magnetic correlations develop above 50 K.

Two magnetic phase transitions occur at 11.0 K and 10.5 K.

High magnetic fields suppress the HT-ICM phase and electric polarization.

Abstract

The low-temperature magnetic phase diagram of the multiferroic system FeTe$_2$O$_5$Br down to 300 mK and up to 9 T is presented. Short-range magnetic correlations within the crystal layers start to develop already at $\sim$50 K, i.e., far above $T_{N1} \sim$ 11.0 K, where the system undergoes a magnetic phase transition into the high-temperature incommensurate (HT-ICM) phase. Only 0.5 K lower, at $T_{N2}$, the system undergoes a second phase transition into the low-temperature incommensurate amplitude-modulated (LT-ICM) phase accompanied by a spontaneous electric polarization. When the magnetic field is applied, the transition temperatures shift depending on the field orientation. In the case of $B||b$ and $B >$ 4.5 T, the HT-ICM phase disappears along with the electric polarization in the LT-ICM phase. The field dependence of the magnetic transition temperatures is explained in the context of the magnetic susceptibility behavior. Similarities and differences between the novel amplitude-modulated and well-established helicoidal magnetoelectrics are discussed.