Geometrical evolution, electronic structures, and magnetic properties of Bi-Mn binary clusters
The geometrical evolution, electronic structures, and magnetic properties of small binary clusters Bi,,Mnm (n≤ 13, m≤6) are investigated using density-functional theory (DFT) with the view of explaining the experi mentally observed magnetic moments in these systems. The results demonstrate that the magnetic moments of the dopant Mn atoms exhibit a weak dependence on the structure, composition, and environment, holding a general constant of 4μB/atom approximately, whereas the magnetic couplings among these Mn atoms are strongly dependent. We propose that the preferred ferromagnetic couplings in the dopant Mnm components result in pronounced magnetic moments represented by certain combinations in which the Bi to Mn ratio is close to 2. Moreover, a faint antiferromagnetic perturbation is provided by the Bi,, units. The hybridization among Mn 3d. Mn 4s, and Bi 6p induces -0.1 μB on B1 atoms and reduces the Mn atomic moments by 1μB. On the whole, the calculated magnetic trends of the different composition series qualitatively fit well with experimental measurements. The lowest-energy structures of the clusters are segregated cases in which the dopant Mnm components assemble together, forming a pentagonal bipyramid shape and surrounded by irregu lar Bin components. Generally, an amorphous configuration is observed for low-Mn-conccntration clusters, but the evolution of a defective polyicosahcdron pattern with a Mn core shell is favored for high-Mn-concentration clusters and this tendency will keep the most stable geometrical structure for larger sizes. By analyzing the binding energies and the second-order energy differences, we find thai the monatomic doping BinMn series containing n=4, 6, 10, and 12 is more stable than its neighboring sizes. Furthermore, the highest occupied and lowest unoccupied molecular orbital gaps decrease as a function of Mn concentration in the clusters, indicating an enhancement of metallicity.
Hong Chen Hong Kuan Yuan An Long Kuang Yue Miao Peng Chen Zhu Hong Xiong
School of Physical Science and Technology, Southwest University, Chongqing, 400715, Peoples Republi School of Physical Science and Technology, Southwest University, Chongqing, 400715, Peoples Republi
国际会议
广州
英文
1387-1401
2008-11-01（万方平台首次上网日期，不代表论文的发表时间）