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.     

First-Principles Study of Magnetic Properties of TM_(13) and TM_(13)@Au_(32) Clusters(TM = Mn,Co)

The structural and magnetic properties of TM_(13 )and TM_(13)@Au_(32 )clusters(TM=Mn,Co)are studied by firstprinciples calculations.We find that the Au_(32 )cluster can tune not only the magnetic moment but also the magnetic coupling properties between the TM atoms of the TM cluster.The Au_(32 )cluster can increase the net magnetic moment of Mn_(13 )clusters while reducing that of Co_(13 )clusters.The interaction between Au and Mn atoms induces more Mn atoms to form spin parallel coupling,resulting in an increase of the total magnetic moment of Mn_(13 )clusters,while for the Co_(13 )clusters,the interaction between Au and Co atoms does not change the magnetic coupling states between the Co atoms,but reduces the magnetic moment of the Co atoms,leading to a decrease of the total magnetic moment of this system.Our findings indicate that the encapsulation of Au_(32 )clusters can not only raise the chemical stability of TM clusters,but also can tune their magnetic coupling properties and magnetic moment,which enables such systems to be widely applied in fields of spintronics and medical science.     

Quantitative test of SO(5) symmetry in the vortex state of Nd(1.85)Ce(0.15)CuO4

By numerically solving models with competing superconducting and antiferromagnetic orders, we study the magnetic field dependence of the antiferromagnetic moment in both the weak and strong field regimes. Through a comparison with the neutron scattering results of Kang et al. and Matsuura et al. on Nd(1.85)Ce(0.15)CuO4, we conclude that this system is close to a SO(5) symmetric critical point. We also make a quantitative prediction on increasing the upper critical field B(c2) and the superconducting transition temperature T(c) by applying an in-plane magnetic field.     

Ni4NdB电子结构和磁性能第一性原理研究

采用第一性原理,在局域自旋密度近似LSDA及LSDA+U近似,对Ni₄NdB化合物进行结构优化,计算体系晶格常数,电子结构和磁性能.结果表明,Ni₄NdB为带隙很小的金属导体,存在Nd-Ni铁磁耦合,体系总磁矩由Nd原子局域磁矩提供.体系原子成键较为复杂,Nd原子与近邻Ni原子成金属键,Nd原子与近邻B原子成较强离子键,Ni原子与近邻Ni原子间存在间接交换相互作用.在U作用下,体系磁矩与Nd原子磁矩变化一致,Ni原子磁矩在2.75 eV呈现磁有序-磁有序崩溃转变 关键词： 密度泛函理论 电子结构 磁性能 稀土过渡金属间化合物     

Effect of samarium impurity on the relaxation of the magnetization of a (NdDy)(FeCo)B alloy

Small Sm additions (~1–3 at %) have been found to slow down the relaxation of the magnetization in a magnetic field in the (NdDy)(FeCo)B alloy by several times. The effective “freezing” of the spontaneous relaxation of the magnetic moment is related to the substantial increase in the potential barriers for motion of domain walls when introducing Sm ions that have other symmetry of the single-ion anisotropy than that of Nd and Dy ions. The results can be used to stabilize the properties of hard magnets.     

Electronic and magnetic structures of Sr(2)FeMoO(6)

We have investigated the electronic and magnetic structures of Sr(2)FeMoO(6) employing site-specific direct probes, namely x-ray absorption spectroscopy with linearly and circularly polarized photons. In contrast to some previous suggestions, the results clearly establish that Fe is in the formal trivalent state in this compound. With the help of circularly polarized light, it is unambiguously shown that the moment at the Mo sites is below the limit of detection (<0.25 mu(B)), resolving a previous controversy. We also show that the decrease of the observed moment in magnetization measurements from the theoretically expected value is driven by the presence of mis-site disorder between Fe and Mo sites.     

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.     

非晶态RE—TM(RE=Nd,Pr,TM=Fe,Co,Ni)薄膜的磁性和Pr的变价行为

本文通过对非晶态轻稀土Pr,Nd和过渡族金属Fe,Co,Ni薄膜合金的低温磁性研究,分别得到了(Pr,Nd)_x-(Fe,Co,Ni)_1-x合金中Pr,Nd和Fe,Co,Ni金属磁矩随成份x的变化,并且通过对磁矩的研究得到Pr离子的4f电子可能有退局域化的结论。 关键词：     

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.     

Magnetization process of Fe layers in Fe/Nd multilayered films investigated by57Fe Mössbauer spectroscopy

The magnetization process of Fe and Nd layers at 5K in Fe/Nd multilayered films with strong perpendicular magnetic anisotropy is elucidated from a comparison of⁵⁷Fe Mössbauer spectra in the presence of the external field applied parallel to the film plane with total magnetization. At zero external field, the film has a magnetic multi-domain structure. The Nd layer moment is perpendicular to the film plane and the Fe layer moment points in the out-of-plane direction. The Fe layer moment monotonically rotates to the in-plane direction with increasing external field parallel to the film plane, while the Nd layer moment is oriented to the film normal direction up to the external field of 10kOe, above which the Nd layer moment gradually turns to the direction of the external field.     

Iron spin-reorientation transition in NdFeAsO

The low-temperature magnetic structure of NdFeAsO has been revisited using neutron powder diffraction and symmetry analysis using the Sarah representational analysis program. Four magnetic models with one magnetic variable for each of the Nd and Fe sublattices were tested. The best fit was obtained using a model with Fe moments pointing along the c-direction, and Nd moments along the a-direction. This signals a significant interplay between rare-earth and transition metal magnetism, which results in a spin-reorientation of the Fe sublattice upon ordering of the Nd moments. All models that fit the data well, including collinear models with more than one magnetic variable per sublattice, were found to have an Fe moment of 0.5 μ(B) and a Nd moment of 0.9 μ(B), demonstrating that the low-temperature Fe moment is not substantially enhanced compared to the spin-density wave state.     

The field and temperature dependence of the magnetic and structural properties of the shape memory compound Ni(1.84)Mn(1.64)In(0.52)

Magnetization and high resolution neutron powder diffraction measurements have been made on the magnetic shape memory alloy Ni(1.84)Mn(1.64)In(0.52). The compound undergoes a broad structural phase transition, which on heating starts at ～150?K and finishes at ～215?K. On cooling there is a ～20?K hysteresis. The high temperature parent phase is cubic (a?=?5.988??) with the L2(1) structure in which the excess Mn atoms occupy the vacancies on the Ni and In sites. The magnetic moment is located mainly on the Mn atoms with the same magnitude on both the 4a (Mn) and 4b (In) sites. The low temperature martensite is monoclinic with parameters a?=?4.405(2), b?=?5.553(2), c?=?12.950(2)??, β?=?86.47(10)°?and space group P2/m. The magnetic properties of the martensitic phase are complex and indicate metamagnetic behaviour.     

Ni5Nd2B4的电子结构和磁性能研究

采用LSDA（Local spin-density approximation）近似及LSDA+U（在位库伦势）近似模拟金属间化合物Ni5Nd2B4的磁性能对于R-M-B合金特性的研究具有重要意义。研究结果显示,LSDA近似下,Ni5Nd2B4具备金属导体性质,晶体结构中最紧邻Ni、B原子间杂化成键,最紧邻Ni-Ni共价成键,Nd、B原子形成成键分子轨道作用,Ni原子间存在自旋消弱现象;LSDA+U近似下,Nd原子磁矩提供体系磁性来源,由于自旋排斥作用Ni原子电子与Nd原子电子自旋方向相反,体系在U值约为6.35eV的作用下能较理想的处理体系电子作用。     

Ni5Nd2B4的电子结构和磁性能研究

采用LSDA（Local spin-density approximation）近似及LSDA+U（在位库伦势）近似模拟金属间化合物Ni5Nd2B4的磁性能对于R-M-B合金特性的研究具有重要意义。研究结果显示,LSDA近似下,Ni5Nd2B4具备金属导体性质,晶体结构中最紧邻Ni、B原子间杂化成键,最紧邻Ni-Ni共价成键,Nd、B原子形成成键分子轨道作用,Ni原子间存在自旋消弱现象;LSDA+U近似下,Nd原子磁矩提供体系磁性来源,由于自旋排斥作用Ni原子电子与Nd原子电子自旋方向相反,体系在U值约为6.35eV的作用下能较理想的处理体系电子作用。     

RKKY ferromagnetism with Ising-like spin states in intercalated Fe(1/4)TaS2

We investigated the magnetic nature of Fe(1/4)TaS2 using x-ray absorption spectroscopy, photoemission spectroscopy, and first principles band calculations. The results show a large unquenched orbital magnetic moment (～1.0 μ(B)/Fe) at intercalated Fe sites, resulting in a gigantic magnetic anisotropy (H(A)?60 T). The magnetic coupling is well understood in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, suggesting a novel RKKY ferromagnet with Ising-type spin states. We also found that this indirect exchange coupling between the neighboring Fe spins is ferromagnetic and maximized at the Fe-Fe distance of 2×2 superstructure.     

The role of N dopant in inducing ferromagnetism in (ZnO)n clusters (n = 1-16)

The effect of nitrogen doping on the magnetic properties of (ZnO)(n) clusters (n = 1-16) has been investigated using spin polarized density functional theory. The total energy calculations suggest that N is more stable at the O site than at the Zn site in (ZnO)(n) clusters and induces a magnetic moment of 1 μ(B)/N atom. The N-Zn-N configuration is more stable than isolated N for 3D structures. The N dopants do not show any tendency for clustering. The binding energy is found to decrease with the increase in the number of N dopants. The magnetic moment increases gradually with the increase in the number of atoms with 1 μ(B)/N atom for n ≤ 4 and less than 1 μ(B)/N for n > 4. The local magnetic moment is mainly localized at the N site with a small magnetic moment induced at the O site. The presence of a Zn vacancy (V(Zn)) induced an additional magnetic moment of 2 μ(B) on the nearest O atoms. The N dopant prefers to form a N-V(Zn) pair. The combination of N and V(Zn) in 3D structures leads to a total magnetic moment of 3 μB. The Mulliken charge transfers from Zn to N and O in all N doped (ZnO)(n) clusters. The calculated results are consistent with existing experimental and theoretical results.     

Role of Nd/Ba disorder on the penetration depth of Nd(1+x)Ba(2-x)Cu(3)O(7-delta) thin films

We report on a study on the effect of Nd/Ba disorder on the ab-plane penetration depth of epitaxial Nd(1+x)Ba(2-x)Cu(3)O(7-delta) thin films. While in stoichiometric samples lambda(T) at low temperature is linear, Nd-rich films exhibit a quadratic law. For low Nd excess (x<0.04), a satisfying fit is obtained using the "dirty" d-wave model assuming that Nd ions at Ba sites act as strong scattering centers. At high x (x>0.15) the data are explained if Nd/Ba disorder becomes less effective as a source of scattering. The effect of localization has been discussed to account for the experimental results.     

First-principles calculations for titanium monoxide clusters TinO （n=1-9）

Based on the density-functional theory, this paper studies the geometric and magnetic properties of TinO （n=1-9） clusters. The resulting geometries show that the oxygen atom remains on the surface of clusters and does not change the geometry of Tin significantly. The binding energy, second-order energy differences with the size of clusters show that Ti7O cluster is endowed with special stability. The stability of TinO clusters is validated by the recent time-of-flight mass spectra. The total magnetic moments for TinO clusters with n=1-4, 8-9 are constant with 2 and drop to zero at n=5-7. The local magnetic moment and charge partition of each atom, and the density of states are discussed. The magnetic moment of the TinO is clearly dominated by the localized 3d electrons of Ti atoms while the oxygen atom contributes a very small amount of spin in TinO clusters.     

Effects of thickness and annealing condition on magnetic properties and thermal stabilities of Ta/Nd/NdFeB/Nd/Ta sandwiched films

Ta/Nd/NdFeB/Nd/Ta sandwiched films are deposited by magnetron sputtering on Si(100) substrates,and subsequently annealed in vacuum at different temperatures for different time.It is found that both the thickness of NdFeB and Nd layer and the annealing condition can affect the magnetic properties of Ta/Nd/NdFeB/Nd/Ta films.Interestingly,the thickness and annealing temperature show the relevant behaviors that can affect the magnetic properties of the film.The high coercivity of 24.1 kOe(1 Oe = 79.5775 A/m) and remanence ratio(remanent magnetization/saturation magnetization)of 0.94 can be obtained in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed for 3 min at 1023 K.In addition,the thermal stability of the film is also linked to the thickness of NdFeB and Nd layer and the annealing temperature as well.The excellent thermal stability can be achieved in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed at1023 K.     

C@Al_(12)团簇吸附H的密度泛函理论研究

利用密度泛函理论的方法研究了C@Al12Hn(1≤n≤7)团簇的结构和稳定性.n为偶数的C@Al12Hn具有更高的稳定性,大的HOMO-LUMO能隙、H原子的结合能以及高的垂直电离势表明这些团簇具有很高的物理和化学稳定性.最高占据分子轨道电荷密度分析显示,偶数n的C@Al12Hn团簇中,一对H原子倾向于占据相反的位置.变形电荷密度分析表明H原子与主体C@Al12之间的结合表现为共价键的特征.对奇数n的C@Al12Hn都具有1μB的磁矩.