Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho

TL;DR

This study uses muon spin relaxation to reveal complex spin state orders and phase separation in layered cobaltites, linking magnetic phases with distinct spin configurations and anisotropic magnetoresistance behaviors.

Contribution

It provides the first microscopic evidence of spin state order and phase separation in RBaCo2O5.5 cobaltites, elucidating their magnetic structures and transport properties.

Findings

Identified three magnetic phases below 300 K.

Observed phase separation with different spin states.

Linked magnetoresistance to phase boundary behavior.

Abstract

We report muon spin relaxation measurements on the magnetic structures of RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one ferrimagnetic and two antiferromagnetic, are identified below 300 K. They consist of different ordered spin state arrangements of high-, intermediate-, and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated regions with different spin state order is observed in the antiferromagnetic phases. The unusual strongly anisotropic magnetoresistance and its onset at the FM-AFM phase boundary is explained.