Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites
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Suvankar Chakraverty Correlated Electron Research Group (CERG) and Cross-Correlated Materials Research Group (CMRG), RIKEN Advanced Science Institute, Wako 351-0198, Japan
Hisanori Mashiko and Takayoshi Oshima Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan
Masashi Kawasaki Correlated Electron Research Group (CERG) and Cross-Correlated Materials Research Group (CMRG), RIKEN Advanced Science Institute, Wako 351-0198, Japan; and Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan (Received 23 August 2012; accepted 14 December 2012)
We have studied the atomic ordering of B-site transition metals and magnetic properties in the pulsed laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6 (LVMO), whose bulk materials are known to be single perovskites with random distribution of the B-site cations. Despite similar ionic characters of constituent transition metals in each compound, the maximum B-site order attained was surprisingly high, ;90% for LCFO and ;80% for LVMO, suggesting a significant role of epitaxial stabilization in the spontaneous ordering process. Magnetization and valence state characterizations revealed that the magnetic ground state of both compounds was coincidently ferrimagnetic with saturation magnetization of ;2 lB per formula unit, unlike those predicted theoretically. In addition, they were found to be insulating with optical band gaps of 1.6 and 0.9 eV for LCFO and LVMO, respectively. Our results present a wide opportunity to explore novel magnetic properties of binary transition metal perovskites upon epitaxial stabilization of the ordered phase. I. INTRODUCTION
Double perovskite oxides are an intriguing class of materials, exhibiting a number of exotic properties such as the high Curie temperature (TC) ferrimagnetism and the half-metallicity.1 Such materials and properties can be potential candidates for a new generation of spinbased devices, thereby have been attracting renewed attention. They are expressed as A2B9B0O6, where A is an alkaline or rare earth element and B9 and B0 are different transition metal elements. Figure 1(a) shows a schematic structure of the double perovskite, where the transition metals occupy the B-site alternately along the [111] direction to form a rock-salt-type sublattice. When 3d and 4d (or 5d) transition metals are combined, a large difference in the formal valences (FV) and ionic a)
Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.438 J. Mater. Res., Vol. 28, No. 5, Mar 14, 2013
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radii (rB) permits spontaneous ordering of transition metal ions, thus facile to synthesize in a bulk form. Representative examples are Sr2Fe31Mo51O6,3 Sr2Fe31Re51O,4,5 and Sr2Cr31Re51O6.6 On the other hand, a few 3d–3d combinations are known to form the ordered phase, such as La2Mn41B0O6 (B0 5 Fe21, Ni21, Co21).7,8 In any c
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