Y(Fe,M)12化合物的电子结构与磁性(M=Nb,Si)

采用新近发展的全势能线性缀加平面波((L)APW) 局域轨道(lo)和广义梯度近似(GGA)密度泛函方法计算了Y(Fe,M)12化合物(M=Nb,Si)的电子结构,得到了相应的总态密度和局域态密度,并分析了替代原子与替代晶位不同引起态密度的变化。根据计算结果预测的居里温度变化与实验结果基本一致。     

NaZn13型Fe基化合物的结构和热力学性质研究

利用Chen-Mbius晶格反演获得的原子间相互作用势,对NaZn13型Fe基金属间化合物进行原子级模拟研究.计算结果表明,Si原子和Co原子均优先占据96i晶位,Si原子和Co原子替代Fe原子后晶体平均结合能降低.随着Co含量的增加,LaFe13-x-yCoySix和NdFe13-x-yCoySix的晶格参数逐渐降低.声子态密度中,稀土原子主要激发低频模,Si原子主要激发高频模.LaFe11.5-yCoySi1.5化合物的德拜温度随Co含量的增加而增高.     

DyFe10Si2化合物的中子粉末衍射测量

氮、碳和氢等原子进入R（Fe，M）12化合物（R=稀土元素，M=Ti，V，Cr，Mn，Mo，W和Si等）可以形成具有优异内禀磁性的间隙型金属间化合物，引起了人们的广泛关注。Dy（Fe，Si）12化合物Si原子择优占据的8f和8j位，不同于其它替代元素的优先占据8i位，且重稀土元素Dy原子磁矩与Fe反平行排列。文中利用中子粉末衍射技术确定了77K温度下DyFe10Si2化合物的晶体结构与磁结构，得到了原子坐标、占位数和磁性原子磁矩等信息。     

Pr_2(Fe_(0.8)Co_(0.2))_(14)B磁结构的中子衍射研究

本文报道用中子衍射测定的含硼稀土过渡族金属间化合物Pr_2(Fe_(0.8)Co_(0.2))_(14)B的晶体结构与磁结构。将中子三轴谱仪用作二轴粉末衍射仪,在室温测该化合物粉末样品的中子衍射强度,用轮廓精化法弥合衍射数据。该化合物属Nd_2Fe_(14)B类四方结构,α=8.8110A,c=12.2307A。设Pr,Fe和Co原子磁矩间为铁磁耦合,同一晶位的Fe,Co原子磁矩相等,存在沿c轴的易磁化方向,得到两个非等效Pr原子晶位Pr4f和Pr4g的磁矩1.2μ_B和1.4μ_B,和六个非等效铁族原子晶位T16k_1,T16k_2,T8j_1,T8j_2,T4e和T4c的磁矩2.2,2.1,1.9,3.1,1.6和1.0μ_B。Co原子在六种非等效晶位上的分布是平均的、等几率的。     

Nd_2(Fe,Si)_(17)合金的结构与磁性

本文对Nd-Fe-Si三元系富铁区域相的结构和磁性进行了研究。结果表明,Nd-Fe-Si三元系富铁区域(Fe>40at％), 除出现NdFe_2Si_2三元金属间化合物外(Si>20at％),同时只出现Nd_2(Fe,Si)_(17)赝二元金属间化合物,其中Si取代9d位的Fe原子,而不能形成类似于Nd_2Fe_(14)B的三元金属间化合物,Si取代Nd_2Fe_(17)中的9d位Fe原子后,使晶胞体积缩小;使饱和磁化强度减小;同时使Fe次晶格的铁磁相互作用增强,导致居里温度增高;还使得Fe次晶格的易面各向异性减弱,造成室温下各向异性场减小。     

3d过渡金属原子单层在Pd(001)表面磁性的第一性原理研究

用第一性原理基础上的超软赝势方法的总能计算，研究了3d过渡金属(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)在Pd(001)表面的单层p(1×1)和c(2×2)结构的表面磁性和总能. 所得结果表明：对于Sc, Ti, V和Cr只存在p(1×1)的铁磁性结构，而Mn只有c(2×2)的反铁磁结构存在. Fe, Co和Ni这三种元素上述两种结构都存在，但是总能上p(1×1)的铁磁结构要低些，因此是比较稳定的结构. 而Cu和Zn在该表面上的单层中不存在上述两种结构. 对于V的p(1×1)铁磁结构，计算得到的每个V原子磁矩为2.41μ_B，大于用全电子方法得到的0.51μ_B. 两种计算方法得到其他金属原子 (Cr，Mn，Fe，Co，Ni)的表面磁矩比较相近，都比孤立原子磁矩略小. 关键词： Pd(001)表面 过渡金属原子单层 表面磁性     

R2Fe17-xAlx化合物中R-T交换耦合常量的计算

讨论了利用分子场近似结合中子衍射或X射线衍射的实验结果计算R2Fe17型稀土过渡族化合物中稀土磁矩与过渡族磁矩之间交换耦合常量的方法,并据此计算了R2Fe17-xAlx(R=Tb,Dy,Ho,Er,Gd,x=7或8)化合物中稀土磁矩与过渡族磁矩之间的交换耦合常量.计算结果与实验值符合较好.     

Y2(Fe1-x-y,Coy,Crx)17化合物的结构及居里温度

通过x射线衍射及磁测量手段研究了Y2(Fe1-y-x,Coy,Crx)17化合物的结构及居里温度.研究结果表明Y2(Fe1-y-x,Coy,Crx)17化合物具有六角相的Th2Ni17型结构.随着x的增加,Y2(Fe1-y-x,Coy,Crx)17化合物的单胞体积呈现先小后大的非线性减小.通过Y2(Fe1-y-x,Coy,Crx)17化合物居里温度的变化,研究了Y2Fe17化合物中哑铃晶位上的Fe原子对之间的交换作用,从而在实验上证明了在Y2Fe17化合物中,哑铃晶位上的Fe原子对之间存在反铁磁交换作用,研究结果表明在Y2Fe17化合物中,Cr,Co同时少量替代Fe时,化合物的居里温度有显著提高.     

RuSi_n(n=1～6)团簇的结构、稳定性和电子性质的密度泛函研究

运用杂化密度泛函理论方法在(U)B3LYP/Lan L2DZ水平研究了Ru Sin(n=1~6)团簇体系的稳定结构及电子性质.结果发现:Ru Sin(n=1~6)团簇基本保持了纯硅团簇的框架.对原子平均束缚能和分裂能的计算表明,Ru Si6团簇是Ru Sin(n=1~6)团簇中热力学稳定性最强的.对自然电荷分布的研究结果发现,Ru Sin(n=2,4~6)团簇的最低能结构出现电荷反转现象.HOMO-LUMO能隙的研究结果表明掺入钌原子后团簇的化学活性增强了,且Ru Si的化学活性是Ru Sin(n=1~6)团簇最强的.通过对团簇磁矩的研究发现,Ru Si和Ru Si3团簇具有了磁性,其余团簇的总磁矩为零,且Ru Sin(n=1~6)团簇中各原子对团簇总磁矩的贡献不同.     

密度泛函理论研究SinMn (n=2～14)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对SinMn (n=2～14) 团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算. 结果表明,当n≥10时,Mn原子完全陷入Si原子形成的笼内.二阶能量差分、分裂能和垂直电离势都表明Si5Mn和Si12Mn是稳定的团簇,且12是团簇的幻数.通过对电子性质的分析发现Si12Mn团簇具有较高的化学稳定性.布局数分析表明,在Si5Mn团簇中Mn原子的磁矩(3.923 μB)是最大的.较多的电荷转移以及Mn原子的4s, 3d态和Si原子的3s, 4p态的较强杂化是导致Mn原子磁矩减小的原因.当n≥7时,SinMn 的总磁矩是1 μB.     

Electronic structure and magnetism of R(Fe,Si)12 (R = Y, Nd)

The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods are briefly introduced, and the structure and magnetic properties of R(Fe, Si)12 compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS) and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that the total magnetic moments of RFe10Si2 (R = Y, Nd) are larger than those of RFe10M2 (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level.     

Electronic structure and magnetism of R(Fe,Si)12 (R = Y, Nd)

The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods are briefly introduced, and the structure and magnetic properties of R(Fe, Si)₁₂ compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS) and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that the total magnetic moments of RFe₁₀Si₂ (R = Y, Nd) are larger than those of RFe₁₀ M ₂ (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level.     

Tunable in-plane spin orientation in Fe/Si(557) film by step-induced competing magnetic anisotropies

Although the spin-reorientation transition from out-of-plane to in-plane in Fe/Si film is widely reported, the tuning of in-plane spin orientation is not yet well developed. Here, we report the thickness-, temperature- and Cu-adsorptioninduced in-plane spin-reorientation transition processes in Fe/Si(557) film, which can be attributed to the coexistence of two competing step-induced uniaxial magnetic anisotropies, i.e., surface magnetic anisotropy with magnetization easy axis perpendicular to the step and volume magnetic anisotropy with magnetization easy axis parallel to the step. For Fe film thickness smaller than 32 monolayer(ML), the magnitudes of two effects under various temperatures are extracted from the thickness dependence of uniaxial magnetic anisotropy. For Fe film thickness larger than 32 ML, the deviation of experimental results from fitting results is understood by the strain-relief-induced reduction of volume magnetic anisotropy.Additionally, the surface and volume magnetic anisotropies are both greatly reduced after covering Cu capping layer on Fe/Si(557) film while no significant influence of Na Cl capping layer on step-induced magnetic anisotropies is observed.The experimental results reported here provide various practical methods for manipulating in-plane spin orientation of Fe/Si films and improve the understanding of step-induced magnetic anisotropies.     

Mn(SiO2)3(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质及磁性

基于密度泛函理论中的广义梯度近似系统研究M_n(SiO₂)₃(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质和磁学性质.结果表明:Fe,Co原子相对于Ni原子更易于在(SiO₂)₃团簇上聚集;通过分析团簇的分裂途径及其产物,发现稳定性较好的氧化硅是一种很好的用于负载过渡金属"岛膜"的载体材料;M_n(SiO₂)₃团簇的能隙恰好位于近红外光谱范围内.通过磁性分析发现,该复合团簇的磁矩主要局域在过渡金属原子周围,而且,Fe₂(SiO₂)₃和Co₃(SiO₂)₃具有相对较大的磁矩,这主要源于过渡金属原子的d轨道间相互耦合.能隙和磁性两方面性质进一步肯定了二氧化硅磁性复合材料在医学界被用作光动力靶向治疗的可观前景.     

Magnetic ordering in semiconducting Tl0.53K0.47Fe1.64Se2 single crystals studied by M?ssbauer spectroscopy

The results of a 57Fe M?ssbauer spectroscopy study between 4.5 and 523.2 K and in external magnetic fields (up to 90 kOe) of semiconducting Tl0.53K0.47Fe1.64Se2 single crystals are reported. Evidence is provided for a possible phase separation into the magnetic majority and minority phases. It is demonstrated that the magnetic moments of the divalent Fe atoms located at the 16i site (space group I4/m) of the majority phase and of the minority phase are antiferromagnetically ordered, with the Néel temperature T(N) = 518.0(3.6) K. The magnetic moments at 5.0 K of 2.09(1) and 2.28(2) μ(B) in these two phases are tilted from the crystallographic c axis by 18(1)° and 32(2)°, respectively. The Debye temperature of Tl0.53K0.47Fe1.64Se2 is found to be 228(4) K.     

Vector magnetization of a Cr monolayer on an Fe(110) film

The non-collinear magnetic moment distribution at the Cr/Fe(110) interface of an Fe(110) thin film covered by a Cr monolayer is revealed by means of periodic Anderson model calculations. It is shown that the Cr surface has two magnetically non-equivalent sites with magnetic moments canted to each other. The Fe atoms in the subsurface monolayer also acquire two magnetically non-equivalent sites with magnetic moments canted to each other. Non-collinearity is shown to be a ground state for the Cr/Fe(110) multilayer.     

A First-Principles Investigation of the Structural and Magnetic Stability of Fe/GaAs(001)

The electronic properties of the interface of Fe/GaAs(001) have been investigated by using first-principles and molecular-dynamics techniques. While the ground state is ferromagnetic for all structures considered, a ferrimagnetic spin structure is found to be very close in energy (<1 meV). The observed lowering of the magnetic moments when relaxing the atomic positions is believed to be connected to this close in energy lying metamagnetic state. On the other hand, the magnetic moments of the Fe atoms at the interface are large, which can be explained by the bulk-like behavior of the density ot states of interface atoms.     

Clusters and magnetic anchoring points in (Ga,Fe)N condensed magnetic semiconductors

The stability and magnetic properties of Fe clusters in the (Ga,Fe)N magnetic semiconductor is investigated by using first-principles density functional theory and local spin density+Hubbard U theoretical methods. The present results reveal the existence of ferrimagnetic clusters formed by three or four peripheral Fe atoms neighboring a central Fe atom acting as a robust magnetic anchoring point. These clusters have magnetic moments 2 or 3 times that of a single Fe atom and, when connected by sharing peripheral Fe atoms, can form stable, ordered magnetic regions where all of the central atoms are ferromagnetically coupled. The formation of these ferrimagnetic clusters is proposed here to be at the origin of the ferromagnetic behavior observed in (Ga,Fe)N samples showing chemical phase separation.     

Magnetic and electronic properties of Cr,Mn, and Fe adatoms on Si(001): A first-principles study

The magnetic and electronic properties of TM (TM=Cr, Mn, and Fe) adatoms adsorption on Si(001) surface are studied by means of the first-principles method. For the adsorption of a single TM atom on Si(001), we obtain decreasing spin moments and increasing adsorption energies as TM varies from Cr to Fe. In the case of TM dimers adsorption, the calculated results show that the spin coupling changes from antiferromagnetic (AFM) to ferromagnetic (FM) as the 3d electrons increased. AFM coupling is found to be preferred for Cr, while FM coupling is energetically favorable for Mn and Fe. In the case of TM wires, we find that the FM state is energetically preferred for Mn and Fe atoms on the Si(001) surface, while for Cr wires, the up–down–up state for P–M–M site Cr atoms seems to be more energy favorable. We also find that the silicon surfaces become metallic for the adsorption of TM wires.     

NEUTRON-POWDER-DIFFRACTION STUDY OF ErFe11.35Nb0.65 AND ErFe11.35Nb0.65Ny

ErFe_11.35Nb_0.65 AND ErFe_11.35Nb_0.65N_y have been synthesized and neutron-powder-diffraction experiments at room temperature performed. The ErFe_11.35Nb_0.65N_y nitride, obtained by gas-solid reaction, retains the ThMn₁₂-type structure of its parent compound. The Nb atoms occupy 8i sites and the nitrogen atoms are located at 2b sites. The atomic magnetic moments of the Er ions are antiparallel to those of the Fe atoms. Upon nitrogenation, the lattice cell expands mainly along the a-axis and the atomic magnetic moments of Fe are enhanced.