Ultrahigh-temperature ferromagnetism in ultrathin insulating films with ripple-infinite-layer structure

TL;DR

This study reports the creation of ultrathin SrFeO2 films exhibiting ferromagnetism and high electrical resistance at room temperature, achieved through strain-induced structural modifications, promising for spintronics and topological electronics.

Contribution

It demonstrates a novel method to realize ultrathin ferromagnetic insulating films with high Curie temperature and robust magnetic properties via strain engineering and selective electron interaction control.

Findings

Resistivity above 10^6 Ohm.cm in SrFeO2 films

Curie temperature extrapolated to 1200 K

Pronounced spin Hall magnetoresistance signals

Abstract

Ferromagnetism and electrical insulation are often at odds, signifying an inherent trade off. The simultaneous optimization of both in one material, essential for advancing spintronics and topological electronics, necessitates the individual manipulation over various degrees of freedom of strongly correlated electrons. Here, by selective control of the spin exchange and Coulomb interactions, we report the achievement of SrFeO2 thin films with resistivity above 106 Ohm.cm and strong magnetization with Curie temperature extrapolated to be 1200 K. Robust ferromagnetism is obtained down to 1.0 nm thickness on substrate and 2.0 nm for freestanding films. Featuring an out of plane oriented ripple infinite layer structure, this ferromagnetic insulating phase is obtained through extensive reduction of as grown brownmillerite SrFeO2.5 films at high compressive strains. Pronounced spin Hall magnetoresistance signals up to 0.0026 is further demonstrated with a Pt Hall bar device. Our findings promise emerging spintronic and topological electronic functionalities harnessing spin dynamics with minimized power dissipations.