Ferromagnetic insulating state in manganites:55Mn study

TL;DR

This study uses 55Mn NMR to investigate the coexistence of ferromagnetic insulating and metallic regions in manganites, revealing different local electronic environments and dynamics within these phases.

Contribution

It provides new insights into the microscopic magnetic and electronic heterogeneity in manganites using 55Mn NMR spectroscopy.

Findings

Identification of two types of regions with distinct NMR spectra and dynamics.

Observation of slower electron hole hopping in insulating clusters.

Temperature-dependent relaxation rates indicating phase coexistence.

Abstract

55Mn NMR was used to study the ferromagnetic insulating state in four different manganites. In all cases the coexistence of two types of regions possessing different NMR spectra and nuclear spin dynamics was found. In the ferromagnetic insulating clusters the hopping frequency fhop of the electron holes is slower comparing to the NMR frequency fres and two lines ascribed to 3+ and 4+ valence states of Mn are observed. The relaxation rate increases rapidly with the increasing temperature, so that these spectra can no longer be observed for temperatures higher than approx 60 K. In ferromagnetic metallic clusters fres < fhop and the motionally narrowed spectrum is observed in a broad temperature interval, as the relaxation remains only moderately fast.