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

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 Bi1-xGdxFeO3 (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 Pn2(1)a 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 MS = 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 x 10(5) 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 anti-ferromagnetic core regions were also found. Such remarkable enhancements in Gd-doped BFO nano-wires might offer a variety of spintronic applications.