New features in the phase diagram of TbMnO$_3$

TL;DR

This study maps the detailed phase diagram of TbMnO₃, revealing how magnetic fields and temperature influence its multiferroic phases and lattice coupling, with new insights into phase boundaries and transitions.

Contribution

The paper provides high-resolution measurements that precisely determine phase boundaries and pressure dependencies, correcting previous assumptions about phase transitions in TbMnO₃.

Findings

Identification of strong coupling between phase transitions and lattice parameters.

Detailed phase boundary mapping including hysteretic regions.

No direct transition from the ferroelectric P||a phase to paraelectric phase in high magnetic fields.

Abstract

The (H,T)-phase diagram of the multiferroic perovskite TbMnO$_3$ was studied by high-resolution thermal expansion $\alpha(T)$ and magnetostriction $\Delta L(H)/L$ measurements. Below $T_{N}\simeq 42$ K, TbMnO$_3$ shows antiferromagnetic order, which changes at $T_{FE}\simeq 28$ K where simultaneously a spontaneous polarization $P||c$ develops. Sufficiently high magnetic fields applied along $a$ or $b$ induce a polarization flop to $P||a$. We find that all of these transitions are strongly coupled to the lattice parameters. Thus, our data allow for a precise determination of the phase boundaries and also yield information about their uniaxial pressure dependencies. The strongly hysteretic phase boundary to the ferroelectric phase with $P||a$ is derived in detail. Contrary to previous reports, we find that even in high magnetic fields there are no direct transitions from this phase to the paraelectric phase. We also determine the various phase boundaries in the low-temperature region related to complex reordering transitions of the Tb moments.