Single-crystalline Gd-doped BiFeO3 nanowires: R3c-to-Pn21a phase transition and enhancement in high-coercivity ferromagnetism

Abstract

We fabricated single-crystalline, Gd-doped BiFeO₃ (BFO) nanowires using a hydrothermal technique. X-ray diffraction (XRD) data combined with their Rietveld refinements and high-resolution transmission electron microscopy (HRTEM) revealed pure single-phase crystalline Bi_1−xGd_xFeO₃ (x = 0, 0.05, 0.10) nanowires of 40–60 nm diameter and their structural transformation from the rhombohedral R3c (for x = 0 and 0.05) to the orthorhombic Pn2₁a crystal structure (for x = 0.10). The addition of Gd³⁺ ions to the pure-phase BFO leads to remarkable changes in the structural and magnetic properties, and these effects are caused by differences in the ionic-radii and magnetic moment between the Bi³⁺ and Gd³⁺ ions. According to the observed magnetization-field (M–H) and magnetization-temperature (M–T) curves, with increasing Gd³⁺ concentration, the saturation magnetization (M_S), squareness (M_r/M_S), coercivity (H_C), exchange-bias field (H_EB) and magnetocrystalline anisotropy (K) increased markedly, by M_S = 1.26 emu g⁻¹ (640%), M_r/M_S = 0.19 (20.5%), H_C = 7788 Oe (4560%), H_EB = 501 Oe (880%) and K = 1.62 × 10⁵ erg cm⁻³ (3500%), for x = 0.10 relative to the data for x = 0. In such Gd-doped BFO nanowire samples, spin-canted Dzyaloshinskii–Moriya interaction, remarkable enhancements in the magnetocrystalline anisotropy as well as uncompensated surface ferromagnetic spin states in the antiferromagnetic core regions were also found. Such remarkable enhancements in Gd-doped BFO nanowires might offer a variety of spintronic applications.