A universal relationship between magnetization and local structure changes below the ferromagnetic transition in La_{1-x}Ca_xMnO_3; evidence for magnetic dimers

TL;DR

This study reveals a universal relationship between magnetization and local structural changes in La_{1-x}Ca_xMnO_3, showing that polaron-related local distortions depend solely on magnetization level, regardless of how it is achieved.

Contribution

It introduces a model linking local structure changes to magnetization via magnetic dimers, highlighting a universal behavior across different doping levels and conditions.

Findings

Local structure changes depend only on magnetization, not on how it is achieved.

Polaron formation correlates with magnetization across temperature and field variations.

Magnetic dimers involving Mn pairs likely pre-form above T_c.

Abstract

We present extensive X-ray Absorption Fine Structure (XAFS) measurements on La_{1-x}Ca_xMnO_3 as a function of B-field (to 11T) and Ca concentration, x (21-45%). These results reveal local structure changes (associated with polaron formation) that depend only on the magnetization for a given sample, irrespective of whether the magnetization is achieved through a decrease in temperature or an applied magnetic field. Furthermore, the relationship between local structure and magnetization depends on the hole doping. A model is proposed in which a filamentary magnetization initially develops via the aggregation of pairs of Mn atoms involving a hole and an electron site. These pairs have little distortion and it is likely that they pre-form at temperatures above T_c.