Nature of magnetic and electronic structure of double perovskite A 2 FeMoO 6 LIANG Pei(梁 培), JIANG Jian-jun(江建军), MA Xin-guo(马新国), TIAN Bin(田 斌) Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China Received 15 July 2007; accepted 10 September 2007 Abstract: The nature of magnetic and electronic structure in double perovskite structure A 2 FeMoO 6 (A = Sr, a, Ca) was calculated using the local spin density approximation (LSDA) and the LSDA+U Coulomb interaction method of density functional theory. The result shows that Sr 2 FeMoO 6 is magnetic metallic material, whereas Ba 2 FeMoO 6 and Ca 2 FeMoO 6 are half-metallic materials. Fe has great effect on the magnetic property of double perovskite structure A 2 FeMoO 6 materials. Because of the orbit hybridization and polarization between the metal element and O element, the Mo element has magnetic properties. The static magnetic moment of double perovskite structure A 2 FeMoO 6 materials, the value of the magnetic moment of these A 2 FeMoO 6 for (A˙Ca, Sr, Ba) are 3.626 43µ B , 2.678 64µ B , 3.706 17µ B , respectively. The magnetic moment of Fe element in the crystal cell are, 3.626 43µ B , 2.678 64 µ B , 3.706 17µ B . And the energy of crystal cells are −28 540.561 907Ry, −24 268.037 272Ry, −44 106.187 179Ry. These values are in agreement with the experiment values. Key words: double perovskite A 2 FeMoO 6 ; full-potential linearized augmented plane wave; half-metal; local density approximation 1 Introduction The growing interest in the development of spintronics devices has stimulated the search for materials with large spin polarization and ferromagnetic order above room temperature[1]. In particular, much effort has been devoted in the past years to the study of ferromagnetic double perovskites of formula A 2 FeMoO 6 (A = Ca, Sr, Ba) triggered by the work of KOBAYASHI et al[1]. The research has mostly been focused on the study of the compound Sr 2 FeMoO 6 (SFMO), which presents a high Curie temperature (T C ≈400 K) and displays a strong magnetoresistance (magnetoresistance is defined as R m = (R(H)−R(0))/R(0), where ρ(H) is the field dependent resistivity) up to room temperature[2]. In the 1960s, GALASSO et al[3] studied some compounds of the type AA′FeMoO 6 and reported that at room temperature a cubic structure for AA′ is Ba 2 , a tetragonal one for AA′ is Sr 2 and an orthorhombic one for AA′ is Ca 2 , as well as a maximum Curie temperature for AA′ is Sr 2 (T C ≈ 420 K). Similar results were reported by NAKAGAWA[4], who also claimed that 8% oxygen vacancies hardly modify the lattice constants and the magnetic behavior. More recently, BORGES et al[5] reported a P21/n monoclinic structure for AA′=Ca 2 and slightly different Curie temperatures. Research also proved that this series of materials to be half metallic ferromagnetic[6]. In despite of many research on this field, there are many open issues of fundamentals importance these concerning the electronic and magnetic structures of compounds. In this article we extended the first principle based on the density function theory to calculate the electronic and magnetic structure of the double perovskites A 2 FeMoO 6 materials. 2 Methods According to the results of BLAHA et al[7], we can obtain the structure of the double perovskites. In order to obtain the most stable structure of A 2 FeMoO 6 ˄A˙Ca， Sr，Ba˅,we used Wien2k [8] to optimize the structure. And then the optimized crystal structure is listed in Table 1. As a preliminary study for the A 2 FeMoO 6 (A˙Ca, Sr, Ba) film, we have investigated electronic and magnetic Foundation item: Project(NCET-04-0702) supported by the New Century Excellent Talents in University of China; Project(50771047) supported by the National Natural Science Foundation of China Corresponding author: LIANG Pei, Doctoral canditate; Tel: +86-27-87559279; E-mail: liangpei20002@yahoo.com.cn