Ultrasonic evidence of an uncorrelated cluster formation temperature in manganites with first-order magnetic transition at T_C

TL;DR

This study uses ultrasonic measurements to identify an uncorrelated cluster formation temperature T* in manganites with first-order magnetic transitions, revealing phase coexistence regions between T_C and T*.

Contribution

It provides experimental evidence of a distinct cluster formation temperature T* in manganites with first-order transitions, supporting phase separation theories.

Findings

Identification of T* > T_C in first-order transition manganites.

Evidence of phase coexistence between T_C and T*.

Transition change from first- to second-order with Sr substitution.

Abstract

Ultrasonic attenuation and phase velocity measurements have been carried out in the ferromagnetic perovskites La_{2/3}Ca_{1/3}MnO_3 and La_{2/3}Sr_{1/3}MnO_3. Data show that the transition at the Curie temperature, T_C, changes from first- to second-order as Sr replaces Ca in the perovskite. The compound with first-order transition shows also another transition at a temperature T* > T_C. We interpret the temperature window T_C < T < T* as a region of coexistence of a phase separated regime of metallic and insulating regions, in the line of recent theoretical proposals.