Exchange bias effect in the phase separated Nd_{1-x}Sr_{x}CoO_3 at the spontaneous ferromagnetic/ferrimagnetic interface

TL;DR

This study investigates the exchange bias effect in phase-separated Nd_{1-x}Sr_{x}CoO_3, revealing how ferrimagnetic and ferromagnetic interfaces influence magnetic properties and cluster sizes at different compositions.

Contribution

It demonstrates the presence of exchange bias in Nd_{1-x}Sr_{x}CoO_3 and analyzes the size and behavior of ferromagnetic clusters related to phase separation.

Findings

Exchange bias appears below the ferrimagnetic transition temperature T_{FI}.

Ferromagnetic cluster sizes are approximately 20 Å for x=0.20 and 40 Å for x=0.40.

Cluster size growth correlates with the weakening of exchange bias at higher Sr doping.

Abstract

We report the new results of exchange bias effect in Nd_{1-x}Sr_{x}CoO_3 for x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state in a spontaneously phase separated system. The zero-field cooled magnetization exhibits the FI (T_{FI}) and ferromagnetic (T_C) transitions at ~ 23 and \sim 70 K, respectively for x = 0.20. The negative horizontal and positive vertical shifts of the magnetic hysteresis loops are observed when the system is cooled through T_{FI} in presence of a positive static magnetic field. Training effect is observed for x = 0.20, which could be interpreted by a spin configurational relaxation model. The unidirectional shifts of the hysteresis loops as a function of temperature exhibit the absence of exchange bias above T_{FI} for x = 0.20. The analysis of the cooling field dependence of exchange bias field and magnetization indicates that the ferromagnetic (FM) clusters consist of single magnetic domain with average size around \sim 20 and ~ 40 \AA ~ for x = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold for x = 0.20, which grow and coalesce to form the bigger size for x = 0.40 resulting in a weak exchange bias effect.