The effects of chromium substitution on the electronic and magnetic properties of CuFeO₂

We present a comprehensive investigation of chromium-substituted delafossite CuFe1-xCrxO2 using synchrotron X-ray diffraction (SR-XRD), X-ray absorption fine structure (XAFS) spectroscopy, and physical property measurements (10-300 K). The studied pristine CuFeO2 exhibits a stable dual-phase structure comprising dominant trigonal-rhombohedral (R-3m, 87.7 wt%) and minor hexagonal (P6(3)/mmc, 12.3 wt%) polymorphs, which persists throughout chromium substitution. Structural analysis reveals chromium incorporation nucleates a secondary hexagonal CuCrO2 phase (P6(3)/mmc) while preserving the host matrix's oxygen stoichiometry, attributable to stronger Fe-O versus Cr-O bonding. XAFS confirms maintained Fe3+ coordination geometry and minimal framework disruption despite Cr substitution. Remarkably, all substituted samples display soft ferromagnetism throughout 10-300 K, contrasting with pure CuFeO2's antiferromagnetic ordering below 11-14 K. This emergent ferromagnetism originates from competing exchange interactions, where introduced ferromagnetic Cr3+-O-Cr3+ pathways (J approximate to +15.4 K) coexist with native antiferromagnetic Fe3+-O-Fe3+ couplings (J approximate to-8.2 K). The findings demonstrate chromium's dual role as both structural stabilizer and magnetic modifier in delafossite oxides..