Role of external and internal perturbations on ferromagnetic phase transitions in manganites: Existence of tricritical points

TL;DR

This paper presents a mean-field theory explaining how external magnetic fields, pressure, and chemical substitution influence the ferromagnetic to paramagnetic phase transition in manganites, revealing the existence of tricritical points where the transition changes order.

Contribution

It introduces a phenomenological model linking external perturbations and chemical substitution to phase transition behavior, validated by experimental data on manganite crystals.

Findings

Existence of tricritical points where transition order changes

External perturbations shift phase boundaries

Model predictions match experimental observations

Abstract

A phenomenological mean-field theory is presented to describe the role of external magnetic field, pressure and chemical substitution on the nature of ferromagnetic (FM) to paramagnetic (PM) phase transition in manganites. The application of external field (or pressure) shifts the transition, leading to a field (or pressure) dependent phase boundary along which a tricritical point is shown to exist where a first-order FM-PM transition becomes second-order. We show that the effect of chemical substitution on the FM transition is analogous to that of external perturbations (magnetic field and pressure); this includes the existence of a tricritical point at which the order of transition changes. Our theoretical predictions satisfactorily explain the nature of FM-PM transition, observed in several systems. The modeling hypothesis has been critically verified from our experimental data from a wide range of colossal magnetoresistive manganite single crystals like Sm$_{0.52}$Sr$_{0.48}$MnO$_3$. The theoretical model prediction of a tricritical point has been validated in this experiment which provides a major ramification of the strength of the model proposed.