NMR evidence for an inhomogeneous transition between the ferromagnetic and antiferromagnetic ground states in Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ manganites

TL;DR

This study uses NMR to reveal that the transition between ferromagnetic and antiferromagnetic states in Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ manganites occurs in an inhomogeneous manner, with mixed magnetic regions and some metallic behavior near the critical concentration.

Contribution

It provides new evidence of inhomogeneous magnetic phase coexistence and fast hopping regions in Pr$_{1-x}$Ca$_{x}$MnO$_{3}$, especially around the critical doping level.

Findings

Inhomogeneous coexistence of ferromagnetic and antiferromagnetic regions.

Presence of fast hopping ferromagnetic regions suggesting metallicity.

Maximum fraction of fast hopping regions at x=0.3.

Abstract

The low temperature behavior of Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ manganites are known to undergo a transition at $x\sim$0.3, from an insulating ferromagnetic state, at low Ca concentration, to an insulating antiferromagnetic state. Above the onset concentration for the charge-ordering effect ($x\sim 0.3$), a metal-insulator transition induced by an external magnetic field is also observed and related to the collapse of the charge-ordered state. In this paper we show that the ferro-antiferromagnetic transition takes place in an inhomogeneous way: around the critical concentration the sample is a mixture of ferromagnetic and antiferromagnetic regions. The zero-field NMR measurements show that a fraction of the ferromagnetic regions is in a fast hopping regime, which suggests that a small fraction of the sample could be metallic, even in zero field. This fraction of fast hopping regions is maximal at $x=$0.3, which is also the concentration for which the insulator-metal transition has been observed in the smallest field.