Specific heat studies of the phase transitions in multiferroic Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$ system ($0 \le x \le 0.65, 0 \le y \le 0.1$)

TL;DR

This study investigates the specific heat anomalies in Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$ across various compositions, revealing phase transition behaviors and the potential for first-order ferroelectric transitions in Ti-doped samples.

Contribution

It provides new insights into the nature of phase transitions in multiferroic Sr-Ba-Mn-Ti-O compounds, especially the transition order change due to Ti doping.

Findings

Magnetic transition anomalies analyzed with advanced theory.

Transition becomes first order in Ti-containing samples.

Ferroelectric anomalies are difficult to detect due to phase coexistence.

Abstract

Specific heat studies of the Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$ polycrystalline samples performed by the relaxation and DSC methods over the temperature range 2 - 450 K are reported. Anomalies accompanying the antiferromagnetic-paramagnetic and ferroelectric-paraelectric phase transitions were measured and analyzed. The system studied is a promising multiferroic material of the 2$^{\text {nd}}$ type, in which a strong coupling between the magnetic and electric systems can be related to the fact that the same Mn$^{4+}$ ions are responsible for the two orderings. Analysis of the anomaly at the magnetic transition was done by using the advanced theory of the continuous transitions, in which the presence of higher order terms in the free energy is considered, and the parameters of the critical behavior of the system were estimated. It was found that, despite of earlier predictions, the transition loses the continuous character and can become the 1$^{\text {st}}$ order process for the Ti-containing samples. The anomalies accompanying the 1$^{\text{st}}$ order high-temperature ferroelectric transition were found to be hardly visible by using both techniques, which was ascribed to a wide temperature range of coexistence of the dielectric and ferroelectric phases.