Sc_nN(n=2～12)团簇的磁性和热容量研究

Investigation of the Magnetic Properties and Heat Capacity of Sc_nN(n=2-12) Clusters

基于第一性原理,在密度泛函理论框架下,用广义梯度近似方法计算了团簇ScnN(n=2～12)的总磁矩Mt、与N原子最近邻的Sc原子的局域磁矩MSc、掺杂原子N的局域磁矩MN.从原子相互作用角度出发,应用统计物理理论,计算了团簇ScnN的磁矩和热容量,研究了它们随温度的变化规律.结果表明:ScnN团簇的磁性与团簇的构型、原子相互作用、磁性粒子间的磁相互作用、团簇中的Sc原子数n有关.总磁矩随Sc原子数n呈波动性变化,当n=3,8,9,11,12时,总磁矩为零,团簇的磁性消失;当n=2,4,5,6,7,10时,团簇表现为铁磁性,其中当n=6时,团簇的磁性最强.ScnN团簇的磁矩随温度升高而减小,其变化趋势与块状磁体类似.温度较低时,磁相互作用产生的热容量CM随温度升高而增大,在某温度附近取极大值;原子相互作用产生的热容量CV在温度较低时与温度成正比,和块状磁体的CV与温度的三次方成正比不同;在对团簇的热容量的贡献中,原子相互作用占主要.

Based on the first principle,the total magnetic moment of ScnN cluster（n=2-12） pMt,the local magnet MSc of Sc atoms which are the closest neighbor of N atoms and the local magnetic moment MN of Sc atoms doped with N atoms are investigated,using generalized gradient approximation（GGA） under the density functional theory framework.The magnetic moment and heat capacity of ScN cluster are studied and their variations with temperature are discussed,applying the statistical physics and based on the atomic interaction.The magnetic moment of ScN cluster is found to be related to the geometry configuration,atomic interaction and magnetic interaction between magnetic particles and the number of Sc atoms（n） in the cluster.The total magnetic moment of the ScnN cluster fluctuates with the number of Sc atoms.The total magnetic moment is zero for n=3,8,9,11 or 12,and the cluster is ferromagnetic for n=2,4,5,6,7 or 10,and the magnetism of cluster Sc6N is the strongest with n=6.The magnetic moment of the ScnN cluster increases with decreasing temperature,showing a similar trend to that of the blocky magnet,i.e.the heat capacity（CM） produced by magnetic interaction increases with rising temperature at a relatively low temperature,and the maximum value occurs when the temperature rises to a certain point.The heat capacity（CV） produced by atomic interaction is proportional to the temperature at a relatively low temperature,which is different from the proportional relationship of CV to the cubic power of temperature of the blocky magnet.Atomic interaction contributes most to the heat capacity of the cluster.