Multicritical end-point of the first-order ferromagnetic transition in colossal magnetoresistive manganites

TL;DR

This study maps the phase diagram of colossal magnetoresistive manganites, revealing a multicritical end-point where the ferromagnetic transition changes from first to second order, influenced by pressure and magnetic field.

Contribution

It identifies the multicritical end-point in the phase diagram of manganites and links the transition character change to reduced charge/orbital fluctuations.

Findings

First-order ferromagnetic transition terminates at a multicritical end-point.

Pressure suppresses the first-order transition, approaching zero at the end-point.

Reduction in charge/orbital fluctuations correlates with transition character change.

Abstract

We have studied the bandwidth-temperature-magnetic field phase diagram of RE(0.55)Sr(0.45)MnO(3) colossal magnetoresistance manganites with ferromagnetic metallic (FM) ground state. The bandwidth (or equivalently the double exchange interaction) was controlled both via chemical substitution and hydrostatic pressure with a focus on the vicinity of the critical pressure p* where the character of the zero-field FM transition changes from first to second order. Below p* the first-order FM transition extends up to a critical magnetic field, H_cr. It is suppressed by pressure and approaches zero on the larger bandwidth side where the surface of the first-order FM phase boundary is terminated by a multicritical end-point (p*~32 kbar, T*~188 K, H*=0). The change in the character of the transition and the decrease of the CMR effect is attributed to the reduced CO/OO fluctuations.