Spin-polarized DFT+U insights into the multifunctional properties of rhombohedral (R3c) GaFeO3

Abstract

We present a spin-polarized first-principles study of rhombohedral (R3c) GaFeO₃ using GGA + U to investigate its structural, elastic, magnetic, electronic, optical, transport, and thermoelectric properties. Cation site disorder is found to be energetically comparable to the ordered phase and induces a ferrimagnetic imbalance, providing a microscopic explanation for experimentally observed weak ferromagnetism. Low-concentration Sr and Ni substitution at Fe sites stabilizes a ferrimagnetic ground state and drives antiferromagnetic-to-ferrimagnetic transitions accompanied by a semiconductor-to-half-metal crossover. Additionally, 6% compressive strain along the c-axis stabilizes a ferromagnetic phase, highlighting the complementary roles of doping and strain engineering. Elastic constants satisfy Born stability criteria, confirming mechanical robustness and magnetoelastic coupling. Magnetic exchange interactions are weak (∼2 meV), suggesting that competing magnetic states may be controlled by electric or intense optical fields, enabling magnetoelectric and magneto-optical effects. Electronic structure and optical analyses reveal tunable band gaps approaching 1.34 eV and strong absorption from the infrared to ultraviolet regions. Carrier transport calculations indicate dominant hole conduction. Thermoelectric properties show strong temperature dependence, with ZT values reaching 3.04 for p-type and ∼1.3 for n-type at 1025 K. These results establish GaFeO₃ as a tunable multifunctional material for thermoelectric, spintronic, and optoelectronic applications.