title: Origin of metallic behavior in NiCo2O4 ferrimagnet.
abstract: Predicting and understanding the cation distribution in spinels has been one of the most interesting problems in materials science. The present work investigates the effect of cation redistribution on the structural, electrical, optical and magnetic properties of mixed-valent inverse spinel NiCo2O4(NCO) thin films. It is observed that the films grown at low temperatures (T < 400 °C) exhibit metallic behavior while that grown at higher temperatures (T > 400 °C) are insulators with lower ferrimagnetic-paramagnetic phase transition temperature. So far, n-type Fe3O4 has been used as a conducting layer for the spinel thin films based devices and the search for a p-type counterpart still remains elusive. The inherent coexistence and coupling of ferrimagnetic order and the metallic nature in p-type NCO makes it a promising candidate for spintronic devices. Detailed X-ray Absorption and X-ray Magnetic Circular Dichroism studies revealed a strong correlation between the mixed-valent cation distribution and the resulting ferrimagnetic-metallic/insulating behavior. Our study clearly demonstrates that it is the concentration of Ni(3+)ions and the Ni(3+)-O(2-)Ni(2+) double exchange interaction that is crucial in dictating the metallic behavior in NCO ferrimagnet. The metal-insulator and the associated magnetic order-disorder transitions can be tuned by the degree of cation site disorder via growth conditions.
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan.
authors.forename: Yugandhar
authors.initials: Y
authors.lastname: Bitla
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Yi-Ying
authors.initials: YY
authors.lastname: Chin
authors.affiliation: Institute of Physics, Academia Sinica, Taipei 105, Taiwan.
authors.forename: Jheng-Cyuan
authors.initials: JC
authors.lastname: Lin
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan.
authors.forename: Chien Nguyen
authors.initials: CN
authors.lastname: Van
authors.affiliation: Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Ruirui
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Yuanmin
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan.
authors.forename: Heng-Jui
authors.initials: HJ
authors.lastname: Liu
authors.affiliation: Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhan
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Hong-Ji
authors.initials: HJ
authors.lastname: Lin
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Chien-Te
authors.initials: CT
authors.lastname: Chen
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan.|Institute of Physics, Academia Sinica, Taipei 105, Taiwan.
authors.forename: Ying-Hao
authors.initials: YH
authors.lastname: Chu
authors.affiliation: Department of Physics, Durham University, Durham DH1 3LE, United Kingdom.
authors.forename: Qing
authors.initials: Q
authors.lastname: He