Novel Field-Induced Phases in HoMnO3 at Low Temperatures

TL;DR

This study uncovers new low-temperature magnetic phases in HoMnO3 induced by magnetic fields, revealing complex phase coexistence and transitions that deepen understanding of multiferroic behavior.

Contribution

It experimentally identifies and characterizes two new field-induced phases in HoMnO3, confirming a predicted intermediate phase and detailing the complex phase diagram at low temperatures.

Findings

Two new phases identified below 76 K for fields up to 50 kOe.

A first-order phase transition with magnetization and entropy jumps observed.

Four phases coexist at a tetracritical point at 2 K and 18 kOe.

Abstract

The novel field-induced re-entrant phase in multiferroic hexagonal HoMnO3 is investigated to lower temperatures by dc magnetization, ac susceptibility, and specific heat measurements at various magnetic fields. Two new phases have been unambiguously identified below the Neel transition temperature, TN=76 K, for magnetic fields up to 50 kOe. The existence of an intermediate phase between the P[6]_3[c]m and P[6]_3c[m] magnetic structures (previously predicted from dielectric measurements) was confirmed and the magnetic properties of this phase have been investigated. At low temperatures (T<5 K) a dome shaped phase boundary characterized by a magnetization jump and a narrow heat capacity peak was detected between the magnetic fields of 5 kOe and 18 kOe. The transition across this phase boundary is of first order and the magnetization and entropy jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of the five low-temperature phases coexist at a tetracritical point at 2 K and 18 kOe. The complex magnetic phase diagram so derived provides an informative basis for unraveling the underlying driving forces for the occurrence of the various phases and the coupling between the different orders.