Thallium substitution effects on Co valence states and room-temperature ferromagnetism in co-doped In2O3: Experimental and machine-learning insights
Year: 2025
Type: article
Abstract: We systematically investigate the effects of thallium (Tl) substitution in Co-doped indium oxide (In₁.₉₋ₓTlₓCo₀.₁O₃), focusing on its influence on Co valence states and magnetic properties. X-ray diffraction (XRD) confirmed that the bixbyite structure was preserved across a wide Tl composition range (x = 0.0-0.6). X-ray photoelectron spectroscopy (XPS) revealed that Tl incorporation increased the Co³⁺/Co²⁺ ratio before annealing. Vacuum annealing induced partial reduction of Co³⁺ to Co²⁺, but higher Tl substitution led to weaker enhancement of ferromagnetic order.Magnetization measurements showed that the pristine (x = 0.0) composition transformed from a paramagnetic to a room-temperature ferromagnetic state upon annealing, while higher Tl content systematically weakened ferromagnetism. These results suggest that the larger ionic radius of Tl³⁺ modifies crystal-field environments and magnetic exchange interactions, promoting Co³⁺ formation yet suppressing long-range ferromagnetism.A machine-learning model using ridge regression predicted the Co³⁺ ratio and room-temperature ferromagnetism (RTF) based on ionic radius and ionization energy with high accuracy (R² ≥ 0.85). Predictions for hypothetical dopants in In₁.₆M₀.₃Co₀.₁O₃ suggested rare-earth elements such as Lu and Pr could enhance Co³⁺ content and ferromagnetic properties.This study highlights how ionic size and ionization energy influence valence states and magnetism in In₂O₃-based diluted magnetic semiconductors, demonstrating the synergy of experiments and machine learning in spintronics material design.
Authors: Asuna Hagiya, Toa Asakura, Taketo Sekiya, Takashi Kataoka, Keiji Komatsu, Keisuke Sato
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,210
OpenAlex ID: W4413364898