Abstract
Epitaxial cobaltites have emerged as exemplary materials for electrochemical gating, in large part due to their topotactic perovskite (P) ↔ brownmillerite (BM) transformations. SrCoO3−δ, for example, can be cycled between metallic ferromagnetic P SrCoO3 and insulating BM SrCoO2.5, realizing exceptional modulation of electronic, thermal, and optical properties. It is often presumed that such cycling also generates ferromagnetic-antiferromagnetic (F-AF) modulation due to the G-type AF order in bulk SrCoO2.5. Little is understood about magnetism in thin-film BM SrCoO2.5, however, meaning that the true magnetic property modulation is unclear. We address this here through a neutron diffraction study of BM La1−xSrxCoO2.5 films at x = 0.5 and 1.0. Lightly compressively strained SrCoO2.5 films are shown to retain G-type AF order, albeit with suppressed Néel temperature (∼340 K). Of high interest for AF spintronics, room-temperature F-AF cycling is thus possible across the SrCoO3-δ P ↔ BM transformation. At x = 0.5, however, BM La0.5Sr.0.5CoO2.5 films are found to exhibit no detectable G-type AF order but instead weak F order (Curie temperature ∼115 K), unveiling a La0.5Sr.0.5CoO3−δ phase diagram with two distinct F phases. These results thus uncover new, unanticipated magnetic phase behavior in these materials, in addition to being directly relevant to cobaltite-based magnetoionics.
| Original language | English |
|---|---|
| Article number | 041123 |
| Journal | APL Materials |
| Volume | 12 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 1 2024 |
Funding
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under Award No. DMR-2011401. Neutron diffraction was supported by the Department of Energy (DOE) through the University of Minnesota (UMN) Center for Quantum Materials under Grant No. DE-SC0016371. Parts of this work were conducted in the UMN Characterization Facility, which is partially supported by NSF through the MRSEC program under Grant No. DMR-2011401, in the Minnesota Nano Center, which is supported by NSF through the National Nanotechnology Coordinated Infrastructure under Grant No. ECCS2025124, and in the UMN Institute for Rock Magnetism, which is supported by NSF (Earth Sciences Division) under Grant Nos. NSF-EAR 1642268, NSF-EAR 2153786, and by UMN. Parts of this work also used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by Oak Ridge National Laboratory.