Competition between ferromagnetism and spin glass: the key for large magnetoresistance in oxygen deficient perovskites SrCo1-xMxO3-d (M = Nb, Ru)

TL;DR

This study investigates how the competition between ferromagnetic and spin glass states in oxygen-deficient SrCo1-xMxO3-d perovskites influences their large negative magnetoresistance, highlighting the roles of Nb and Ru substitutions.

Contribution

It reveals the magnetic interactions and disorder caused by Nb and Ru substitutions as key factors for large magnetoresistance in these cobaltites.

Findings

Weak ferromagnetism with transition temperatures up to 180 K.

Spin glass behavior below 80-90 K.

Magnetoresistance reaching 30% at 5 K in 7 T.

Abstract

The magnetic and magnetotransport properties of the oxygen deficient perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and Ru-substituted cobaltites are weak ferromagnets, with transition temperatures Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass behavior at temperatures below Tf = 80-90 K. It is demonstrated that there exists a strong competition between ferromagnetism and spin glass state, where Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites induces magnetic disorder, and this particular magnetic behavior is the origin of large negative magnetoresistance of these oxides, reaching up to 30% at 5 K in 7 T. The differences between Nb- and Ru-substituted cobaltites are discussed on the basis of the different electronic configuration of niobium and ruthenium cations.