Half-Metallicity and Magnetic Anisotropy in Double-Perovskite GdBaCo₂O₆ Films Prepared via Topotactic Oxidation

Abstract

Double-perovskite GdBaCo2O x is a promising material owing to its fascinating electronic and magnetic features, such as spin crossover, charge and spin-state ordering, magnetic-field or photo-induced antiferromagnetic-to-ferromagnetic phase transition, and large magnetoresistance (MR). These properties can be controlled by changing the oxygen content (x), and an increase of x is effective for stabilizing ferromagnetic order. However, a stoichiometric phase (x = 6) has not yet been obtained because the distorted coordination geometry prefers oxygen vacancies. In this study, we report the successful synthesis of GdBaCo2O6 epitaxial films via the topotactic oxidation of a film with x = 5.5. The transformation between x = 5.5 and 6 phases was reversible via low-temperature redox reactions. The x = 6 film exhibited ferromagnetic and metallic behavior below the Curie temperature (T C) of 110 K and semiconducting behavior above T C. The spontaneous magnetization of the x = 6 film was 4.8 μB/f.u., which is the largest in the double-perovskite cobaltite system owing to the ferromagnetic interaction between Co3.5+ and Gd3+. It also exhibited strong magnetic anisotropy along the a axis (1.7 × 107 erg/cm3) and anisotropic MR behavior associated with the Gd/Ba ordering along the c axis. Furthermore, theoretical calculations predicted that the half-metallicity of the x = 6 film originates from the double exchange interaction between intermediate-spin Co3+ and low-spin Co4+.

Cation-placement control in double-perovskite GdBaCo2O6 and its impact on magnetism via spin-state modification

“…Subsequently, the as-grown films were oxidized by treatment with NaClO solution at 80 °C for 40 h, following the same procedure reported for the fabrication of A-site-ordered GdBaCo 2 O 6 films. 6 In contrast to the as-grown films, the oxidized films exhibit ferromagnetic behavior below T C . Moreover, the M values of the oxidized films are significantly higher than those of the as-grown films, which confirms successful oxidation via NaClO treatment.…”

“…At present, stoichiometric A-site-ordered RBaCo 2 O 6 (R = Pr, Gd, and Y) is prepared via low-temperature topotactic oxidation using NaClO solution. 6,[24][25][26][27] The film thickness obtained is typically 30-40 nm. The crystal structures of the films were evaluated using X-ray diffraction (XRD) measurements.…”

“…These distinctive properties, including the ferrimagnetic half-metallicity of Sr 2 FeMoO 6 and the extremely high magnetoresistivity of NdBaMn 2 O 6 , arise from complex lattice distortion and magnetic coupling between the ordered cations. [1][2][3] In particular, A-siteordered double-perovskite cobaltites GdBaCo 2 O x (x = 5-6) exhibit a rich variety of magnetic and electronic features, including high magnetoresistance, 4,5 spin-crossover-associated metal-insulator transition, 5 high magnetic anisotropy, [5][6][7] half-metallicity, 6 and magnetic field (H)-or photoinduced phase transitions from antiferromagnetic to ferromagnetic states. 4,5,[7][8][9][10] Furthermore, GdBaCo 2 O x exhibits excellent electrochemical properties, including fast oxygen-ion conductivity, anisotropic oxide-ion and proton conductivity, and efficient catalytic behavior.…”

Structural, electronic, magnetic, and optical properties of RE2ZrZnO6 (RE= La, Dy and Ho) double perovskites: experimental and DFT studies

“…It was noted that the GGA+U and GGA values did not differ from one another. Exchange splitting of La-4f, Dy-4f, Ho-4f, Zr-3d, and Zn-3d states electrons are the main reason behind the total magnetic moment values [48]. The total magnetic moment of a material is defined as the difference between the values of magnetic moment produced by the up and down spin states.…”