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1.
The g-factors of the intra-band states 12,13,14,15 in a magnetic-rotational band built on the 11 state in 82 Rb are measured for the first time by using a transient magnetic field-ion implantation perturbed angular distribution (TMF-IMPAD) method.The magnetic-rotational band in 82 Rb is populated by the 60 Ni(27 Al,4pn) 82 Rb reaction,and the time-integral Larmor precessions are measured after recoil implantation into a polarized Fe foil.The calculation of g-factors is also carried out in terms of a semi-classical model of independent particle angular momentum coupling on the basis of the four-quasiparticle configuration π(g 9/2) 2 π(p 3/2,f 5/2) ν (g 9/2).The measured and calculated g-factors are in good agreement with each other.The g-factors and deduced shear angles decrease with the increase of spin along the band.This clearly illustrates the shear effect of a step-by-step alignment of the valence protons and neutrons in magnetic rotation.The semi-classical calculation also shows that the alignment of the valence neutron angular momentum is faster than that of the valence protons,which results in a decrease of g-factors with increasing spin.The present results provide solid evidence of the shear mechanism of magnetic rotation. 相似文献
2.
Nearly-spherical nuclei in three mass regions have recently been observed to exhibit rotational-like features. We have identified
almost 80 such bands; largest number (43) lie in the lead region. Most of these bands are assigned oblate multi-quasiparticle
configurations. Their interpretation in terms of ‘magnetic rotation’ does not allow for signature splitting in these bands.
We have however found signature splitting as well as signature inversion in many bands. We apply the two-quasiparticle plus
rotor model to understand the occurrence of signature splitting vis-a-vis the role of ‘shears mechanism’ in these bands. 相似文献
3.
A two-dimensional tilted axis cranking Hartree-Fock-Bogoliubov (CHFB) calculation is performed for 76Kr and 78Kr nuclei up to high spins J = 30 employing a pairing-plus-quadrupole (PPQ) model interaction Hamiltonian. Intricate details of the evolution of single
particle structures and shapes as a function of spin have been investigated. The results show the existence of energy levels
with high K quantum numbers lying close to the yrast line in both the nuclei. Such high K states should exhibit isomeric characteristics due to the K-selection rules for the γ-decays. Moreover, in 78Kr a new band with J = 20–30 lying below the observed ground band is predicted.
相似文献
4.
N. Aoi S. Kanno S. Takeuchi H. Suzuki D. Bazin M.D. Bowen C.M. Campbell J.M. Cook D.-C. Dinca A. Gade T. Glasmacher H. Iwasaki T. Kubo K. Kurita T. Motobayashi W.F. Mueller T. Nakamura H. Sakurai M. Takashina J.R. Terry K. Yoneda H. Zwahlen 《Physics letters. [Part B]》2010
The neutron-rich nucleus 74Ni was studied with inverse-kinematics inelastic proton scattering using a 74Ni radioactive beam incident on a liquid hydrogen target at a center-of-mass energy of 80 MeV. From the measured de-excitation γ rays, the population of the first 2+ state was quantified. The angle-integrated excitation cross section was determined to be 14(4) mb. A deformation length of δ=1.04(16) fm was extracted in comparison with distorted wave theory, which suggests that the enhancement of collectivity established for 70Ni continues up to 74Ni. A comparison with results of shell model and quasi-particle random phase approximation calculations indicates that the magic character of Z=28 or N=50 is weakened in 74Ni. 相似文献
5.
M.M. Rahman R. MuhidaM.S.H. Chowdhury H. Zainuddin B.Z. Azmi H. Kasai 《Current Applied Physics》2012,12(3):794-797
We investigate oxygen dissociative adsorption to a platinum monolayer on Ni(110) surface (Pt/Ni(110)) by density functional theory. We have shown that the activation barrier on Pt/Ni(110) is lower than that on a clean Pt(001) surface. This may be due to the effect of magnetization of Pt surface. The reason of decrease of activation barrier can be attributed to the flow of electrons from oxygen to platinum surface because the d orbitals have spin polarization at the Fermi level where the down spin d orbitals are unoccupied. 相似文献
6.
7.
The structural, electronic and magnetic properties of TMGen (TM=Mn, Co, Ni; n=1-13) have been investigated using spin polarized density functional theory. The transition metal (TM) atom prefers to occupy surface positions for n<9 and endohedral positions for n≥9. The critical size of the cluster to form endohedral complexes is at n=9, 10 and 11 for Mn, Co and Ni respectively. The binding energy of TMGen clusters increases with increase in cluster size. The Ni doped Gen clusters have shown higher stability as compared to Mn and Co doped Gen clusters. The HOMO-LUMO gap for spin up and down electronic states of Gen clusters is found to change significantly on TM doping. The magnetic moment in TMGen is introduced due to the presence of TM. The magnetic moment is mainly localized at the TM site and neighbouring Ge atoms. The magnetic moment is quenched in NiGen clusters for all n except for n=2, 4 and 8. 相似文献
8.
Zheng W Cleveland ZI Möller HE Driehuys B 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(2):284-290
When hyperpolarized noble gases are brought into the bore of a superconducting magnet for magnetic resonance imaging (MRI) or spectroscopy studies, the gases must pass through substantial field gradients, which can cause rapid longitudinal relaxation. In this communication, we present a means of calculating this spatially dependent relaxation rate in the fringe field of typical magnets. We then compare these predictions to experimental measurements of (3)He relaxation at various positions near a medium-bore 2-T small animal MRI system. The calculated and measured relaxation rates on the central axis of the magnet agree well and show a maximum (3)He relaxation rate of 3.83×10(-3) s(-1) (T(1)=4.4 min) at a distance of 47 cm from the magnet isocenter. We also show that if this magnet were self-shielded, its minimum T(1) would drop to 1.2 min. In contrast, a typical self-shielded 1.5-T clinical MRI scanner will induce a minimum on-axis T(1) of 12 min. Additionally, we show that the cylindrically symmetric fields of these magnets enable gradient-induced relaxation to be calculated using only knowledge of the on-axis longitudinal field, which can either be measured directly or calculated from a simple field model. Thus, while most MRI magnets employ complex and proprietary current configurations, we show that their fringe fields and the resulting gradient-induced relaxation are well approximated by simple solenoid models. Finally, our modeling also demonstrates that relaxation rates can increase by nearly an order of magnitude at radial distances equivalent to the solenoid radius. 相似文献
9.
采用密度泛函理论和slab模型,研究NH3在Ni单原子层覆盖的Pt(111)和WC(001)表面上的物理与化学行为,计算了Ni单原子覆盖表面的电子结构以及NH3的吸附与分解.表面覆盖的单原子层中,Ni原子的性质与Ni(111)面上的Ni原子明显不同.与Ni(111)相比,Ni/Pt(111)和Ni/WC(001)表面上Ni原子dz2轨道上的电子更多地转移到了其它位置,该轨道上电荷密度降低有利于NH3吸附.在Ni/Pt(111)和Ni/WC(001)面上NH3吸附能均大于Ni(111),NH3分子第一个N-H键断裂的活化能则明显比Ni(111)面上低,有利于NH3的分解,吸附能增大使NH3在Ni/Pt(111)和Ni/WC(001)面上更倾向于分解,而不是脱附.N2分子的生成是NH3分解的速控步骤,该反应能垒较高,说明N2分子只有在较高温度下才能生成.WC与Pt性质相似,但Ni/Pt(111)和Ni/WC(001)的电子结构还是有差异的,与Ni(111)表面相比,NH3在Ni/Pt(111)表面上分解速控步骤的能垒降低,而在Ni/WC(001)上却升高.要获得活性好且便宜的催化剂,需要对Ni/WC(001)表面做进一步改进,降低N2分子生成步骤的活化能. 相似文献
10.
The local electronic structure and magnetic properties of GaAs doped with 3d transition metal (Sc, Ti, V, Cr, Mn, Fe, Co,
Ni) were studied by using discrete variational method (DVM) based on density functional theory. The calculated result indicated
that the magnetic moment of transition metal increases first and then decreases, and reaches the maximum value when Mn is
doped into GaAs. In the case of Mn concentration of 1.4%, the magnetic moment of Mn is in good agreement with the experimental
result. The coupling between impure atoms in the system with two impure atoms was found to have obvious variation. For different
transition metal, the coupling between the impure atom and the nearest neighbor As also has different variation.
Supported by the National Natural Science Foundation of China (Grant No. 10347010) 相似文献
11.
采用密度泛函理论中广义梯度近似对非典型富勒烯C22和过渡金属内掺衍生物M@C22(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C22的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用. 相似文献
12.
文章介绍了原子核协变密度泛函理论的历史发展、理论框架、对原子核基态和激发态的描述以及在一些交叉学科领域的应用。首先,通过回顾原子核物理研究中的几个重要里程碑并结合二十一世纪原子核物理面临的机遇和挑战,对当前核物理的研究热点和重要课题进行了介绍。随后系统介绍了原子核协变密度泛函理论,内容包括协变密度泛函理论的历史发展、一般理论公式、介子交换模型、点耦合模型、交换项、张量相互作用、物理观测量的计算公式等。协变密度泛函理论的应用包括原子核基态性质和激发态性质的描述以及在核天体物理与标准模型检验中的应用。其中,基态性质包括原子核结合能、半径、单粒子能级、共振态、磁矩、晕现象等。激发态性质包括原子核磁转动、低激发态性质、集体转动、量子相变、集体振动等。在核天体物理与标准模型检验的应用中,主要以核纪年法测算宇宙年龄和Cabibbo-Kobayashi-Maskawa矩阵的幺正性检验等为例,介绍协变密度泛函理论在交叉学科领域的应用。 相似文献
13.
The electron paramagnetic resonance g factors and the local structure for Ni3+ in LaAl0.9Ni0.1O3 (LAN), La0.75Y0.25Al0.99Ni0.01O3 (LYAN) and YAl0.9Ni0.1O3 (YAN) are theoretically studied from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt are taken into account. According to the calculations, the ligand octahedra around Ni3+ are suggested to suffer 2% relative elongation along the [001] (or C4) axis due to the Jahn-Teller effect. 相似文献
14.
The structure of the collective bands in77Kr is investigated within our deformed shell model (DSM) based on Hartree-Fock states. The different levels are classified
into collective bands on the basis of their B(E2) values. The calculatedK = 5/2+ ground band agrees reasonably well with the experiment. An attempt has been made to study the structure of the 3-quasiparticle
band based on large J state in this nucleus. The calculated collective bands, the B(E2), and B(M1) values are compared with
available experimental data. The nature of alignments in the low-lying bands is also analyzed. 相似文献
15.
W.L. Feng X.M. Li W.C. Zheng Y.G. YangW.Q. Yang 《Journal of magnetism and magnetic materials》2011,323(5):528-531
The EPR g factors, g|| and g⊥, for the isoelectronic 3d9 ions Ni+ and Cu2+ at the tetragonal Cu+ site of the CuGaSe2 crystal are calculated from the high-order perturbation formulas based on a two-spin-orbit-parameter model. In the model, both the contributions to g factors from the spin-orbit parameter of central 3d9 ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ0, where θ is the angle between the metal-ligand bond and C4 axis, and θ0≈54.74° is the same angle in cubic symmetry) of Ni+ and Cu2+ centers, which are different from the corresponding angle in the host CuGaSe2 crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g||−g⊥ between the isoelectronic Ni+ and Cu2+ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe2 crystal. 相似文献
16.
Cuijing GuoWei Zhang Rongjin JiYanwei Zeng 《Journal of magnetism and magnetic materials》2011,323(5):611-615
Multi-doped YIG ferrites {Y1.7Gd0.5Ca0.8}[Fe2−xInx](Fe2.15V0.4Mn0.05Al0.4)O12 (x=0, 0.3, 0.6, 0.7, 0.8 and 0.9) with low saturation magnetizations (4πMs=400-600 G at 298 K) were prepared by a conventional ceramic technology and the effects of In3+-substitution on their structures and magnetic properties were systematically investigated using XRD, SEM and VSM. It has been found that as-synthesized powders and sintered ferrites showed a single-phase of garnet structure with a cell parameter (a) that increased linearly with increase in In3+ concentration from x=0 up to 0.9. Apparent relative densities of sintered samples were all over 98%, but no remarkable influences of In3+-substitution were observed by SEM on the refinement of crystal grains and the enhancement of sintering of ferrites. In addition, the Curie temperature Tc decreased almost linearly as In3+concentration increased, while the corresponding saturation magnetization at room temperature presented a variation characterized by a gradual increase first and then a rapid plunge. On the basis of quantitative analysis of XRD data and the theory on super-exchange interactions, it has been established that the incorporated In3+ ions via doping were exclusively located at the sites with octahedral coordinations in the crystal structure and the aforementioned magnetic properties can be simply attributed to weakening super-exchange interactions between neighboring magnetic ions through oxygen ions due to the “dilution effect” of added non-magnetic In3+ ions. 相似文献
17.
The complete diagonalisation (of energy matrix) method based on the two-spin-orbit-parameter model is applied to unifiedly calculate the spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) and optical band positions for Ni+ ion in silver gallium selenide (AgGaSe2) crystal. In the model, besides the contribution due to the spin-orbit parameter of central dn ion (i.e., the one-spin-orbit-parameter model in the traditional crystal-field theory), that of ligand ions are taken into account. The calculated results are reasonably consistent with the experimental values. The local structure of Ni+ centre in AgGaSe2 is estimated through the calculation. The complete diagonalisation method based on the one-spin-orbit-parameter model is also applied to calculate these electron paramagnetic resonance and optical data. It is found that although the calculated optical band positions are close to those based on the two-spin-orbit-parameter model and hence to the experimental values, the calculated spin-Hamiltonian parameters (in particular, the g factors) are in disagreement with the experimental values. The latter point is further confirmed from the calculations with the perturbation method. So, for the rational calculations of spin-Hamiltonian parameters of dn clusters with ligand having large spin-orbit parameter, the contributions due to spin-orbit parameters of both the central dn ion and ligand ion should be contained. 相似文献
18.
基于第一性原理,在密度泛函理论框架下,用广义梯度近似(GGA)研究了二十面体Y12TM(TM=Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn)团簇的电子结构和磁性,计算了它们的束缚能(BE)、中心原子到表面原子的间距、最高占据轨道(HOMO)、最低占据轨道(LUMO)及其能隙.研究表明:Y13、Y12Sc、Y12Ti、Y12V、Y12Cr团簇的主体原子和杂质原子呈现出铁磁性作用,而Y12Mn、Y12Fe、Y12Co、Y12Ni、Y12Cu、Y12Zn团簇的主体原子和杂质原子呈现出反铁磁作用. 相似文献
19.
First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3
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The effects of La and Sb doping on the electronic structure and optical properties of SrTiO 3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO 6 octahedra dominate the main electronic properties of SrTiO 3 , and its structural stability can be improved by La doping. The La 3+ ion fully acts as an electron donor in Sr 0.875 La 0.125 TiO 3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb 0.125 Ti 0.875 O 3 , there is a distortion near the bottom of the CBs for SrSb 0.125 Ti 0.875 O 3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr0.875La0.125TiO3 and SrSb0.125Ti0.875O3 , respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95% in most of the visible region, which is higher than that of Sr0.875La0.125TiO3 (85%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb0.125 Ti0.875 O3 . 相似文献
20.
The Born-Oppenheimer (BO) equilibrium molecular structure () of cis-methyl formate has been determined at the CCSD(T) level of electronic structure theory using Gaussian basis sets of at least quadruple-ζ quality and a core correlation correction. The quadratic, cubic and semi-diagonal quartic force field in normal coordinates has also been computed at the MP2 level employing a basis set of triple-ζ quality. A semi-experimental equilibrium structure () has been derived from experimental ground-state rotational constants and the lowest-order rovibrational interaction parameters calculated from the ab initio cubic force field. To determine structures, it is important to start from accurate ground-state rotational constants. Different spectroscopic methods, applicable in the presence of internal rotation and used in the literature to obtain “unperturbed” rotational constants from the analysis and fitting of the spectrum, are reviewed and compared. They are shown to be compatible though their precision may be different. The and structures are in good agreement showing that, in the particular case of cis-methyl formate, the methyl torsion can still be treated as a small-amplitude vibration. The best equilibrium structure obtained for cis-methyl formate is: r(Cm-O) = 1.434 Å, r(O-Cc) = 1.335 Å, r(Cm-Hs) = 1.083 Å, r(Cm-Ha) = 1.087 Å, r(Cc-H) = 1.093 Å, r(CO) = 1.201 Å, ∠(COC) = 114.4°, ∠(CCHs) = 105.6°, ∠(CCHa) = 110.2°, ∠(OCH) = 109.6°, ∠(OCO) = 125.5°, and τ(HaCOC) = 60.3°. The accuracy is believed to be about 0.001 Å for the bond lengths and 0.1° for the angles. 相似文献