Phase Stability and Structural Evolution of Core/Shell Iron Oxide Nanoparticles Due to Oxidative Diffusion: Implications for Spintronic Applications

Nuñez, Jorge M. ; Lima, Enio ; Lohr, Javier Hernán ; Vásquez Mansilla, Marcelo ; Zysler, Roberto D. ; Tolley, Alfredo ; Bartolomé, Fernando ; Rubín, Javier (Universidad de Zaragoza) ; Hettler, Simón ; Arenal, Raúl ; Aguirre, Myriam Haydee (Universidad de Zaragoza) ; Winkler, Elin L.

Resumen: Core/shell iron oxide nanoparticles are promising candidates for spintronic applications due to their tunable magnetic properties and interfacial exchange interactions that allow the modulation of spin-polarized conduction. However, their performance depends critically on phase stability and structural integrity under fabrication and operating conditions involving thermal and oxidative diffusion. This study examines the transformation of iron oxide nanoparticles induced by oxidative diffusion in thermal annealing from wüstite to hematite through an intermediate (wüstite)-core/(magnetite–maghemite)-shell structure. The nanoparticles exhibit a rounded cubic morphology, with a distorted C2/m FeO phase at the core under compressive strain along (010), while the Fe3O4 shell exhibits tensile strain along (110). Oxygen diffusion occurs preferentially along [100] from the cube faces, influencing shape evolution. The system exhibits an exchange bias field of up to 3 kOe and enhanced magnetic hardening of up to 4 kOe, attributed to interfacial exchange interactions. Higher annealing temperature promotes the formation of γ-Fe2O3 with ordered vacancies. The exchange bias effect persists, even when the FeO core is smaller than 1 nm in size, indicating that the strain stabilizes the antiferromagnetic (AFM) order and enhances core/shell magnetic coupling. As oxidation proceeds, strain is gradually relaxed, and at 873 K, the oxidation to hematite is promoted, characterized by a Morin transition at 245 K. These findings reveal the intricate relationship between oxidation-driven structural evolution and magnetic behavior in engineered nanoparticle systems, underscoring the critical importance of material selection tailored to specific fabrication processes, operating conditions, and device performance requirements.

Idioma: Inglés

DOI: 10.1021/acsanm.5c01929

Año: 2025

Publicado en: ACS APPLIED NANO MATERIALS 8, 25 (2025), 13024-13036
ISSN: 2574-0970

Financiación: info:eu-repo/grantAgreement/ES/DGA/E13-23R
Financiación: info:eu-repo/grantAgreement/EC/H2020/101007629 /EU/Nanomaterials for Enzymatic Control of Oxidative Stress Toxicity and Free Radical Generation/NESTOR
Financiación: info:eu-repo/grantAgreement/EC/H2020/101007825/EU/ULtra ThIn MAgneto Thermal sEnsor-Ing/ULTIMATE-I
Financiación: info:eu-repo/grantAgreement/EC/H2020/872631 /EU/Memristive and multiferroic materials for emergent logic units in nanoelectronics/MELON
Financiación: info:eu-repo/grantAgreement/ES/MICIU/CEX2023-001286-S
Financiación: info:eu-repo/grantAgreement/ES/MICIU/PID2023-151080NB-I00

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Cienc.Mater. Ingen.Metal. (Dpto. Ciencia Tecnol.Mater.Fl.)
Área (Departamento): Área Física Materia Condensada (Dpto. Física Materia Condensa.)