TY - JOUR
T1 - Composition-induced structural, electrical, and magnetic phase transitions in AX-type mixed-valence cobalt oxynitride epitaxial thin films
AU - Takahashi, Jumpei
AU - Hirose, Yasushi
AU - Oka, Daichi
AU - Nakao, Shoichiro
AU - Yang, Chang
AU - Fukumura, Tomoteru
AU - Harayama, Isao
AU - Sekiba, Daiichiro
AU - Hasegawa, Tetsuya
N1 - Publisher Copyright:
© 2015 AIP Publishing LLC.
PY - 2015/12/7
Y1 - 2015/12/7
N2 - Synthesis of mid- to late-transition metal oxynitrides is generally difficult by conventional thermal ammonolysis because of thermal instability. In this letter, we synthesized epitaxial thin films of AX-type phase-pure cobalt oxynitrides (CoOxNy) by using nitrogen-plasma-assisted pulsed laser deposition and investigated their structural, electrical, and magnetic properties. The CoOxNy thin films with 0 ≤ y/(x + y) ≤ 0.63 grown on MgO (100) substrates showed a structural phase transition from rock salt (RS) to zinc blend at the nitrogen content y/(x + y) ∼ 0.5. As the nitrogen content increased, the room-temperature electrical resistivity of the CoOxNy thin films monotonically decreased from the order of 105 Ω cm to 10-4 Ω cm. Furthermore, we observed an insulator-to-metal transition at y/(x + y) ∼ 0.34 in the RS-CoOxNy phase, which has not yet been reported in Co2+/Co3+ mixed-valence cobalt oxides with octahedral coordination. The low resistivity in the RS-CoOxNy phase, on the 10-3 Ω cm order, may have originated from the intermediate spin state of Co3+ stabilized by the lowered crystal field symmetry of the CoO6-nNn octahedra (n = 1, 2,⋯5). Magnetization measurements suggested that a magnetic phase transition occurred in the RS-CoOxNy films during the insulator-to-metal transition. These results demonstrate that low-temperature epitaxial growth is a promising approach for exploring novel electronic functionalities in oxynitrides.
AB - Synthesis of mid- to late-transition metal oxynitrides is generally difficult by conventional thermal ammonolysis because of thermal instability. In this letter, we synthesized epitaxial thin films of AX-type phase-pure cobalt oxynitrides (CoOxNy) by using nitrogen-plasma-assisted pulsed laser deposition and investigated their structural, electrical, and magnetic properties. The CoOxNy thin films with 0 ≤ y/(x + y) ≤ 0.63 grown on MgO (100) substrates showed a structural phase transition from rock salt (RS) to zinc blend at the nitrogen content y/(x + y) ∼ 0.5. As the nitrogen content increased, the room-temperature electrical resistivity of the CoOxNy thin films monotonically decreased from the order of 105 Ω cm to 10-4 Ω cm. Furthermore, we observed an insulator-to-metal transition at y/(x + y) ∼ 0.34 in the RS-CoOxNy phase, which has not yet been reported in Co2+/Co3+ mixed-valence cobalt oxides with octahedral coordination. The low resistivity in the RS-CoOxNy phase, on the 10-3 Ω cm order, may have originated from the intermediate spin state of Co3+ stabilized by the lowered crystal field symmetry of the CoO6-nNn octahedra (n = 1, 2,⋯5). Magnetization measurements suggested that a magnetic phase transition occurred in the RS-CoOxNy films during the insulator-to-metal transition. These results demonstrate that low-temperature epitaxial growth is a promising approach for exploring novel electronic functionalities in oxynitrides.
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U2 - 10.1063/1.4937431
DO - 10.1063/1.4937431
M3 - Article
AN - SCOPUS:84949595349
VL - 107
JO - Applied Physics Letters
JF - Applied Physics Letters
SN - 0003-6951
IS - 23
M1 - 231906
ER -