The electronic and magnetic behavior of low-dimensional double-exchange materials

The two-dimensional double-exchange material La x Sr 2 -xMnO4 is studied using density functional theory within the local-density approximation. The electronic structures of Sr 2 MnO 4 , La 2 MnO 4 , denoted by A 2 BO 4 , as well as La x Sr 2-x MnO 4 (x = 0.5, 1, 1.5) are analyzed in detail. The band structures of these materials present different characteristics according to the amount of covalent interaction between A and O, which varies due to the competition between the A-O and B-O interactions. According to total energy calculations, the most stable phase of La 2 MnO 4 is ferromagnetic metal, while that of Sr 2 MnO 4 is antiferromagnetic insulator. In the states around the Fermi level, the largest contribution is of Mn 3d in La 2 MnO 4 , The coupling between Mn 3d and O 2p is strong in Sr 2 MnO 4 and reduces as La is introduced in this material. The impurity effects are discussed for La x Sr 2 -x MnO 4 .