Computer Modeling and Simulation Group, College of Engineering, University of Akron, OH 44325-3905, USA.
J Phys Condens Matter. 2010 Jun 23;22(24):246001. doi: 10.1088/0953-8984/22/24/246001. Epub 2010 Jun 1.
The crystal structure, electronic and magnetic properties of LaMn(7)O(12) ((LaMn(3)(3+))(A)Mn(4)(3+)O(12)) are investigated by GGA (LSDA) and GGA + U (LSDA + U) (0.0 ≤ U ≤ 5.0 eV) methods. Based on two experimentally refined structures (distinguished by the distortion parameter Δ, namely S(I) (Δ = 8.5 × 10(-5)) and S(II) (Δ = 25.0 × 10(-4))), GGA and GGA + U with U < 3.0 eV calculations indicate that S(I) with a small distortion is the lowest-energy crystal structure while GGA + U with 3.0 ≤ U ≤ 5.0 eV calculations show that S(II) with a larger distortion is the ground-state crystal structure. Within the LSDA method, S(II) is always the ground-state structure no matter if U is considered or not. There are two independent magnetic sublattices: Mn(3+) within the A site and Mn(3+) within the B site. First, it is predicted that A-site Mn(3+) ions are preferably AFM-coupled in G-type (antiferromagnetically coupled in three directions). Based on this result, four magnetic configurations (FM-[Formula: see text], AFM1-[Formula: see text], AFM2-[Formula: see text] and AFM3-[Formula: see text]) are designed, and their total energies are calculated. Our results demonstrate that AFM2 and AFM3 are the lowest magnetic state, respectively, for S(I) and S(II). Correspondingly, LaMn(7)O(12) is metallic with no orbital ordering at AFM2 for S(I) while it is an insulator with orbital ordering at AFM3 for S(II). Thus, modulation of the distortion parameter Δ, e.g. by chemical doping, could be employed as a new avenue to induce a magnetic phase transition and the corresponding metal-to-insulator transition in LaMn(7)O(12).
采用 GGA（LSDA）和 GGA + U（LSDA + U）（0.0≤U≤5.0 eV）方法研究了 LaMn(7)O(12)（((LaMn(3)(3+))(A)Mn(4)(3+)O(12))）的晶体结构、电子和磁性能。基于两个经过实验细化的结构（由畸变参数 Δ区分，即 S(I)（Δ=8.5×10(-5)) 和 S(II)（Δ=25.0×10(-4))），GGA 和 U<3.0 eV 的 GGA + U 计算表明，小畸变的 S(I)是最低能量的晶体结构，而 3.0≤U≤5.0 eV 的 GGA + U 计算表明，大畸变的 S(II)是基态晶体结构。在 LSDA 方法中，无论是否考虑 U，S(II) 始终是基态结构。存在两个独立的磁子晶格：A 位的 Mn(3+)和 B 位的 Mn(3+)。首先，预测 A 位 Mn(3+)离子优先在 G 型（三个方向反铁磁耦合）中 AFM 耦合。基于此结果，设计了四种磁构型（FM-[Formula: see text]，AFM1-[Formula: see text]，AFM2-[Formula: see text]和 AFM3-[Formula: see text]），并计算了它们的总能量。结果表明，对于 S(I)，AFM2 和 AFM3 分别是最低的磁态；对于 S(II)，分别是 AFM2 和 AFM3。相应地，LaMn(7)O(12)在 S(I)中为 AFM2 时为金属，无轨道有序，而在 S(II)中为 AFM3 时为绝缘体，具有轨道有序。因此，通过化学掺杂调制畸变参数 Δ，例如，可以作为诱导 LaMn(7)O(12)中磁相变和相应的金属-绝缘体相变的新途径。
