Enhancement of giant magnetoresistance effect in the Ruddlesden-Popper phase Sr3Fe2-xCoxO7-d: Predominant role of oxygen nonstoichiometry and magnetic phase separation

TL;DR

This study explores how oxygen nonstoichiometry and magnetic phase separation enhance the giant magnetoresistance in Sr3Fe2-xCoxO7-d, revealing a strong link between magnetic disorder and GMR effects at low temperatures.

Contribution

It demonstrates the role of magnetic phase separation and oxygen content in controlling GMR in Sr3Fe2-xCoxO7-d, a novel insight into magnetic disorder effects.

Findings

GMR effect up to 80% at 5 K in 7 T

Magnetic disorder correlates with enhanced negative MR

Segregation into ferromagnetic clusters influences GMR

Abstract

The magnetic and magnetotransport properties of the Sr3Fe2-xCoxO7-d system (0.2 <= x <= 1.0) were systematically investigated. This oxide system exhibits a giant magnetoresistance (GMR) effect at low temperatures, reaching up to 80% in 7 T at 5 K. Ac-susceptibility measurements show that there exists a strong competition between ferromagnetic (F) and spin glass states, and the balance between these two magnetic states can be controlled by varying cobalt (x) and/or oxygen contents (d). Importantly, the MR effect is closely related to the magnetic property: the development of magnetic disordering leads to enhancement in the negative MR effect. It is suggested that the compound segregates into F clusters embedded in a non-F matrix, being a naturally occurring analog of the artificial granular-GMR materials, as in the doped perovskite cobaltites, La1-xSrxCoO3 (x < 0.18).