Strong local structural distortion and magnetic order suppression in spin-driven multiferroic BaYFeO4 upon Co doping

Abstract

Understanding the interplay between structural, electronic, and magnetic properties is essential for unraveling the unique magnetic phenomena and spin-driven ferroelectricity in BaYFeO4 and related compounds. Herein, we present a comprehensive study on the effects of cobalt doping on the structural, electronic, and magnetic properties of BaYFe1−xCoxO4 polycrystals (x = 0–0.15), using a combination of X-ray and neutron powder diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, and magnetic measurements. The initial orthorhombic Pnma crystal structure remains stable upon Co doping, though local structural changes arise due to the complex spin states of Co3+ ions. These ions adopt low-spin and high-spin configurations depending on their coordination, respectively, while Fe3+ ions retain a high-spin state. All samples exhibit an incommensurate collinear spin-density wave antiferromagnetic order at the Néel temperature TN1, which, evolves into a cycloidal antiferromagnetic order at a lower TN2. These long-range magnetic orders are gradually suppressed with increasing Co content. Additionally, the onset temperature of short-range magnetic correlations—emerging well above TN1—decreases with increased doping. These findings highlight the significant influence of Co doping on both intrachain and interchain magnetic interactions, governing the overall magnetic behavior of BaYFe1−xCoxO4. The underlying mechanisms are discussed in detail.