Tricritical Point and the Doping Dependence of the Order of the Ferromagnetic Phase Transition of La1-xCaxMnO3

TL;DR

This study investigates how the order of the ferromagnetic phase transition in La1-xCaxMnO3 varies with doping, identifying a tricritical point that separates first and second order transitions through magnetization and specific heat measurements.

Contribution

It provides the first detailed doping-dependent analysis of the transition order in La1-xCaxMnO3, identifying a tricritical point and characterizing critical exponents.

Findings

First order transition at x=0.33 with entropy change of 2.3 J/molK.

Continuous transition at x=0.4 with tricritical exponents.

Tricritical point separates first and second order transitions.

Abstract

We report the doping dependence of the order of the ferromagnetic metal to paramagnetic insulator phase transition in La1-xCaxMnO3. At x = 0.33, magnetization and specific heat data show a first order transition, with an entropy change (2.3 J/molK) accounted for by both volume expansion and the discontinuity of M ~ 1.7 Bohr magnetons via the Clausius-Clapeyron equation. At x = 0.4, the data show a continuous transition with tricritical point exponents alpha = 0.48+/- 0.06, beta = 0.25+/- 0.03, gamma = 1.03+/- 0.05, and delta = 5.0 +/- 0.8. This tricritical point separates first order (x<0.4) from second order (x>0.4) transitions.