Effect of V5+/V4+ substitution on structural and magnetic orderings of SrFeO3-δ

Abstract

SrFeO3-δ is a structurally versatile material, showing cubic (C) symmetry at δ = 0, which transitions to tetragonal (T) and then orthorhombic (Or) with increasing oxygen vacancies. These structural changes alter magnetic behavior through variations in bond angles and lengths, enabling both antiferromagnetic (AFM) and ferromagnetic (FM) interactions between Fe4+/Fe3+ ions and oxygen (or vacancies). While such tunable magnetic phases offer rich physics and potential applications, achieving room-temperature (RT) FM remains challenging. This study explores V5+/V4+ doping in SrFeO3-δ (SrFe1-xVxO3-δ

0 ≤ x ≤ 0.03) to induce FM persisting up to RT and investigates its structural-magnetic correlation. Structural analysis from X-ray diffraction (XRD) and Raman spectroscopy, supported by phonon mode calculations, reveals that SrFeO3-δ is in a mixed T-Or phase. At the same time, V-doped samples exhibit an emerging C-phase in a dominant T-lattice. Magnetic hysteresis (M − H) loops show notable FM behavior within the AFM matrix at low temperature ∼10K, with a FM and paramagnetic phase at room temperature. Temperature-dependent magnetization measurements indicate a T-phase related Néel temperature (TN) shift from 70K to 55K in the doped samples as compared to the pure one. An increased magnetization difference between the field-cooled (FC) and zero-field-cooled (ZFC) data with increasing V-content suggests an increasing magnetic frustration due to competing FM/AFM exchange interactions. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) analyses reveal a rise in Fe3+ and V5+ states, affecting oxygen vacancy distributions and corresponding structural shifts seen in XRD and Raman results. The multivalent Fe3+/Fe4+ and V4+/V5+ states enhance Double-Exchange (DE) interactions (Fe3+-O-Fe4+ and Fe3+-O-V5+), and VO-mediated Fe3+-VO-Fe3+ interaction, promoting ferromagnetism. Moreover, frequency-dependent magnetization studies display a subtle susceptibility peak shift, indicating spin-glass-like behavior in V-doped samples. © 2025