最近邻相互作用对混合自旋Blume-Capel模型磁化强度的影响（英文）

利用有效场论研究了最近邻原子间交换相互作用对纳米管晶格点磁化强度的影响.研究结果表明,最近邻交换相互作用和晶场强度相互竞争,使系统表现出丰富的磁化特性.当负晶场作用于系统时,系统存在一级相变.当晶场参数和交换相互作用不同时,系统磁化强度表现出奇异性.     

最近邻弱交换相互作用对spin-1纳米管磁化强度的影响

利用有效场理论研究了纳米管上最近邻原子间弱交换相互作用对Blume-Capel模型磁化强度的影响,得到了系统格点的磁化强度与最近邻弱交换相互作用和晶场强度的关系。结果表明：最近邻弱交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出丰富的磁学特性。正晶场促进系统的磁化强度,而负晶场对其有抑制作用;负晶场作用下,磁化强度基态饱和值小于1,且系统发生一级相变;不同位置的弱交换相互作用对系统的磁化强度影响程度不同。     

最近邻原子间交换相互作用对纳米管上Blume-Capel模型磁热性质的影响

利用有效场理论研究了纳米管上最近邻原子间交换相互作用对Blume-Capel模型格点的磁化强度、内能、比热和自由能的影响,得到了系统格点的磁化强度、内能、比热和自由能与交换相互作用和晶场强度的关系.结果表明:最近邻交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出丰富的磁学特性;正晶场对系统磁化强度具有促进作用;负晶场对系统磁化强度具有抑制作用;负晶场作用下,系统发生一级相变;晶场强度参数和交换相互作用不同时,系统的内能、比热和自由能也呈现出奇异性.     

最近邻弱交换相互作用对纳米管中Blume-Capel模型热学性质的研究

利用有效场理论研究了纳米管上最近邻弱交换相互作用下spin-1纳米管中Blume-Capel模型的内能、比热和自由能,得到了系统的内能、比热和自由能与最近邻弱交换相互作用和晶场的关系。结果表明：最近邻弱交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出比 = = =1时的BC模型更为复杂的热学性质;系统内能随温度的变化曲线表现出不连续性;比热随温度的变化出现奇异性;高温对自由能的影响更加明显。     

最近邻强交换相互作用对spin-1纳米管热力学性质的影响

利用有效场理论研究了纳米管上最近邻强交换相互作用下Blume-Capel模型的内能、比热和自由能,得到了系统的内能、比热和自由能与最近邻强交换相互作用、晶场强度和温度的关系.结果表明:最近邻强交换相互作用、晶场强度和温度等诸多因素相互竞争,使系统表现出比J_1=J_2=J=1时的BC模型更为丰富的热力学性质;系统内能随温度的变化曲线表现出不连续性;比热随温度的变化出现奇异性;一定条件下,基态时的自由能会发生突变.     

外壳层最近邻交换相互作用对Blume-Capel模型相变行为的影响

利用有效场理论研究了纳米管上双模随机晶场中混合自旋Blume-Capel模型的相变行为。结果表明，系统相变行为与取值概率、晶场强度比值、晶场参数、温度以及外壳层最近邻交换相互作用密切相关。取值概率、晶场强度比值、晶场参数和外壳层最近邻交换相互作用等诸多因素相互竞争，影响系统的一级和二级相变以及临界点。     

双模随机交错晶场中最近邻弱交换相互作用对重入现象的影响

利用有效场理论研究了双模随机交错晶场中混合自旋 Blume-Capel 模型纳米管系统的重入现象, 发现了系统的重入现象与晶场取值概率、 晶场强度和外壳层与内壳层格点间最近邻交换相互作用的关系. 结果表明: 取值概率、 交换相互作用、 晶场强度和温度等诸多因素相互竞争, 使系统表现出丰富的磁化现象: 正( 负) 晶场较弱时, 系统只发生二级相变; 随着正( 负) 晶场增强, 系统的二级相变消失, 呈现一级相变; 一定条件下, 系统会出现重入现象.     

外磁场对纳米管上Blume-Capel模型磁热性能的研究

利用有效场理论研究了纳米管上外磁场中Blume-Capel模型格点的磁化强度、磁化率、内能、比热和自由能,得到了系统格点的磁化强度、磁化率、内能、比热和自由能与外磁场和晶场的关系.结果表明:外磁场强度、交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出比没有外磁场作用的Blume-Capel模型更为丰富的磁学特性;外磁场能够增大系统格点的磁化强度,导致系统的二级相变消失;负晶场作用系统时,系统会发生一级相变;晶场强度、外磁场强度不同时,系统的磁化率、内能、比热和自由能也呈现出复杂性.     

双模随机交错晶场对spin-1和spin-1/2混合自旋纳米管中Blume-Capel模型磁化强度的影响

利用有效场理论研究了纳米管上双模随机交错晶场中混合自旋Blume-Capel模型格点的平均磁化强度，得到了系统格点的平均磁化强度与双模随机晶场的取值概率、外磁场、晶场参数和晶场强度比值的关系.结果表明:取值概率、外磁场、交换相互作用、晶场强度比值和晶场强度等诸多因素相互竞争，使系统表现出比恒定晶场作用的Blume-Capel模型更为丰富的磁化现象;双模随机交错晶场会抑制系统的平均磁化强度，使其基态饱和值小于5/6;外磁场导致系统的二级相变消失;一定条件下系统发生一级相变;系统的平均磁化强度呈现部分缺失和负值现象.     

铁磁球/反铁磁纳米体系磁滞回线的Monte Carlo模拟

利用经典Heisenberg模型和Monte Carlo方法研究外磁场和反铁磁磁晶各向异性、交换相互作用对铁磁球均匀嵌入到反铁磁基体中的铁磁/反铁磁纳米体系磁滞回线的影响.模拟结果显示,外加反向最大磁场不同时,磁滞回线形状不同.当磁场正向增加时,体系的磁化强度会产生一个跃变,但跃变高度与反向场最大值无关.反铁磁磁晶各向异性越大,体系的交换偏置现象越明显,且磁化强度回到饱和值所需的外磁场越大.随着反铁磁基体交换相互作用的增大,在正向和负向磁场区域还可能出现新的磁滞现象.     

Thermodynamic properties of Heisenberg model for magnetic ordered graphene sheet

We study the thermodynamic properties of two dimensional Heisenberg antiferromagnet on the honeycomb lattice in the presence of anisotropic Dzyaloshinskii-Moriya interaction and next nearest neighbor coupling exchange constant. A sublattice antiferromagnetic long range ordering has been considered for localized electrons on honeycomb lattice structure. In particular, the temperature dependence of specific heat has been investigated for various physical parameters in the model Hamiltonian. Using Holstein-Primakoff bosonic transformations, the behavior of thermodynamic properties has been studied by means of excitation spectrum of mapped bosonic gas. Furthermore we have studied the dependence of specific heat and magnetization on Dzyaloshinskii-Moriya interaction strength for various next nearest neighbor interaction strengths. At low temperatures, the specific heat is found to be monotonically increasing with temperature. We have found the dependence of specific heat on Dzyaloshinskii-Moriya interaction strength shows a monotonic increasing behavior for various next nearest neighbor exchange constants. Also we have studied the temperature dependence of staggered magnetization for different next nearest neighbor coupling constants. Our results show the critical temperature moves to higher amounts with reduction of Dzyaloshinskii-Moriya interaction strength.     

稀释晶场对spin-1和spin-1/2混合自旋纳米管中 Blume-Capel模型磁化强度的研究

利用有效场理论研究了纳米管上稀释晶场中混合自旋Blume-Capel模型格点的磁化强度,得到了系统格点的磁化强度与稀释晶场取值概率、外磁场和晶场的关系.结果表明:取值概率、外磁场、交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出比恒定晶场作用的Blume-Capel模型更为丰富的磁学特性;外磁场能够增大系统格点的磁化强度,导致系统的二级相变消失;负晶场的作用使系统发生一级相变;稀释晶场会抑制系统的磁化强度,导致其基态饱和值小于1.     

双模随机同向晶场对spin-1和spin-1/2混合自旋纳米管中Blume-Capel模型平均磁化强度的影响

利用有效场理论研究了纳米管上双模随机同向晶场中混合自旋Blume-Capel模型格点的平均磁化强度,得到了系统格点的平均磁化强度与双模随机晶场的取值概率、外磁场、晶场参数和晶场强度比值的关系。结果表明：取值概率、外磁场、交换相互作用、晶场强度比值和晶场强度等诸多因素相互竞争,使系统表现出比恒定晶场作用的Blume-Capel模型更为丰富的磁化现象;双模随机同向晶场会抑制系统的平均磁化强度,使其基态饱和值小于5/6;外磁场导致系统的二级相变消失;一定条件下系统发生一级相变;系统的平均磁化强度呈现部分缺失和负值现象。     

The thermal behaviors and phase diagrams of the Ising-type endohedral fullerene with magnetic core and diluted magnetic shell (Core@Shell<Subscript>20</Subscript>)

We have carried out theoretical studies on Ising-type endohedral fullerene (EF) structure with a dopant magnetic atom encaged within the diluted magnetic spherical cage to examine the evolution in magnetic behaviors. We show how the thermal behaviors and phase diagrams of Ising-type EF are affected by diluted surface, crystal field and exchange couplings. We have used to investigate theoretically the effect of Hamiltonian parameters the effective field calculations within Ising model framework. The model Hamiltonian includes nearest neighbor ferromagnetic and antiferromagnetic center-surface (C-S) interaction as well as ferromagnetic surface interaction. We have shown that the system exhibits the first and second order phase transitions as well as tricritical point. In particular, the conditions for the occurrence of these reentrant and double reentrant behaviors are given explicitly.     

Monte Carlo study of small magnetic particles

In earlier computer simulation small magnetic particles with nearest neighbor Heisenberg interactions in zero magnetic field have been studied. We now continue these investigations including next nearest neighbor exchange and non zero magnetic fieldsH. The particles treated have spherical shape with a number of spinsN in the range from 33 to 3071. It is shown that the spontaneous magnetization of the particles is rather different from the bulk magnetization. The magnetization process can be accounted for by the Néel theory, if the correct spontaneous magnetization of the particle is used. The distribution of local magnetizations (the magnetic “profile”) was also obtained in various cases. It is shown that the magnetization of very small particles is much more depressed than predicted by the mean field approximation. We introduce an “effective magnetic radius” \(\hat R\) accounting for the reduction of the local magnetization. This magnetic radius is important for the interpretation of experimental results. A distinct dependence of \(\hat R\) on the magnetic field, temperature and the fraction of next nearest neighbor exchange is found. Finally a brief comparison is made with the recent study of magnetic surface properties by Binder and Hohenberg.