Temperature Dependence of the Magnetic Hyperfine Field at 140Ce on Gd Sites in GdAg Compound

Perturbed gamma–gamma angular correlation technique was used to measure the magnetic hyperfine field at Gd sites in the intermetallic compound GdAg using the ¹⁴⁰La→¹⁴⁰Ce nuclear probe. A major and well-defined magnetic interaction is observed at ¹⁴⁰Ce substituting Gd sites in GdAg below 130 K, corresponding to a ferromagnetic ordering of Gd moments. The temperature dependence of magnetic hyperfine field, however, shows a sharp deviation from an expected Brillouin-like behavior for temperatures below 75 K. This additional magnetic interaction is believed to result from the polarization of Ce spin moments induced by the magnetic field from Gd atoms.     

Investigation of Hyperfine Interactions in GdNiIn Compound

Perturbed gamma–gamma angular correlation technique was used to measure the hyperfine interactions in the compound GdNiIn using the ¹¹¹InCd → and ¹⁴⁰La¹⁴⁰Ce probe nuclei at the In and Gd sites, respectively. A unique quadrupole frequency with asymmetry parameter η = 0.78 was observed for ¹¹¹Cd probe at In sites for the measurements above Curie temperature. Below T _C , the spectra for ¹¹¹Cd show combined magnetic dipole and electric quadrupole interaction. Below 85 K, a unique magnetic interaction is observed at ¹⁴⁰Ce. A linear relationship between the saturated magnetic hyperfine field and the magnetic transition temperature was observed for both probes, indicating that the main contribution to the mhf comes from the conduction electron polarization.     

Hyperfine Magnetic Anomaly in Atomic Spectra of Rare-Earth Elements

The constants of the hyperfine splitting in the atomic optical spectra of the rare-earth elements – Nd, Eu, Gd and Lu – were measured. The method of laser resonance fluorescence in the parallel atomic beam was used. The values of the hyperfine magnetic anomaly were determined from the comparision of magnetic dipole constant ratios of the neighbouring odd Z or N isotopes for the different atomic levels. The connection of these values and the parameters of atomic and nuclear structure is discussed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Fields in Complex Metallic Systems: Co Clusters Embedded in Cu

We have used first-principles linear muffin tin orbital (LMTO-ASA) electronic structure calculations, implemented directly in real space (RS) to theoretically investigate the behavior of the hyperfine field of Co clusters embedded in fcc Cu. We find that the magnitude of the dominant contact contribution to the hyperfine field decreases significantly as one goes from the Co site at the center of the cluster to those at the Co–Cu interface. To better understand this behavior, we use a simple model which closely reproduces the first-principles calculations, but is physically more transparent. Our approach can partially deconvolute the several dependences, calling attention to the processes which regulate the hyperfine field behavior in these complex Co–Cu systems.     

Anisotropy of the Hyperfine Field on 57Fe in Pure and Substituted Yttrium Iron Garnet

Using NMR, anisotropy of the hyperfine field on ⁵⁷Fe nuclei was measured in Y₃Fe₅O₁₂ with nonmagnetic, trivalent substitutions on d (Ga³⁺) and a (Y³⁺ - yttrium antisite defect) sites which are occupied by ferric ions in a pure, stoichiometric system. The measurements were performed by the spin-echo method at liquid helium temperature. Thorough analysis of the hyperfine field anisotropy on the ⁵⁷Fe nuclei in an ideal environment and in an environment where one of Fe³⁺ nearest cation neighbours is replaced by the nonmagnetic impurity is given. When the Fe³⁺ on which the NMR is measured is on the a site and the impurity is Ga³⁺(d), the results may be interpreted in terms of the superposition model. On the other hand, the results for Fe³⁺ on the d site and Y³⁺(a) are in clear disagreement with the predictions of this model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hyperfine Interaction of 111Cd in Fe3Sn Compound

The hyperfine interaction of ¹¹¹Cd in ferromagnetic Fe₃Sn compound was investigated by TDPAC in the paramagnetic region and below the Curie temperature. The results are compared with hyperfine magnetic fields and EFGs on ¹¹¹Cd and ¹¹⁹Sn in other stoichiometric Fe–Sn phases. This revised version was published online in September 2006 with corrections to the Cover Date.     

Perturbed Angular Correlation Study of Magnetic and Electric Hyperfine Interactions at 111Cd in GdNi2 and SmNi2

The magnetic hyperfine field B _hf of the closed-shell probe nucleus ¹¹¹Cd in the C15 Laves phase RNi₂ (R= Gd, Sm) has been investigated as a function of temperature by perturbed angular correlation (PAC) spectroscopy. The saturation magnetic hyperfine fields at 10 K are B _hf=7.7(2) and 3.9(1) T for GdNi₂ and SmNi₂, respectively. Although the probe nucleus resides on the cubic rare-earth site, a strong axially symmetric electric quadrupole interaction (QI) is observed in the paramagnetic phase at T300 K. The possible relation of this unexpected QI to the structural instability of RNi₂ is discussed.     

强磁场下Cs原子超精细塞曼能级上的光泵浦研究

强磁场中的Ｃｓ原子有较大的超精细塞曼分裂，实验用频率可调谐的窄线宽半导体激光调谐到各超精细塞曼能级上进行光泵浦，利用稳态吸收谱方法研究了原子的光泵浦。表明基态超精细相互作用的碰撞修正项导致的驰豫跃迁是谱形状和电子自旋极化新特征的根缘。同时提出了强场下极化度的一种测量方法。     

Study of Hyperfine Fields in CeIn3 by Electronic Structure Calculations

Electronic band structure calculations for the CeIn₃ compound utilizing the full potential linearized augmented plane waves method were performed with the aim to compute the hyperfine fields acting on Ce and In atoms. The latter are found to be in reasonable agreement with the values measured at low temperatures. The 4f orbital contribution dominates the magnetic hyperfine field at Ce ions while the contact field is negligible due to an almost complete cancellation of valence and core contributions. A non-zero magnetic hyperfine field appears at In sites due to the spin-polarization of the 5p sub-shells through the hybridization with the extended 6s, 6p and 5d Ce states which, in turn, are spin-polarized by the Ce 4f states. No net magnetic moment at In is observed since the sum of its 5p sub-shell spins is zero. The 5p shell of In is responsible for the presence of an electric field gradient at In nuclei. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Interactions at 181Ta in Hf2Co7

In this paper we report a time differential perturbed angular correlation (TDPAC) study of hyperfine interactions at ¹⁸¹Ta in Hf₂Co₇ compound. The TDPAC measurements have been performed in the temperature range 77–1023K. The measured spectra showed broad distribution of hyperfine interactions up to 388K. Above this temperature, in a reversible manner, two nuclear electric quadrupole interactions (EQI) have been observed: at 393K, _Q1=449.0(27)MHz, ₁=0.00(4) and _Q2=144.7(41)MHz, ₂=0.44(2). Since the Curie temperature for this compound is known from the literature to be around 420K, only magnetic order transition could be responsible for such an observation. However, the measurements of magnetization did not exhibit any drastic change in this temperature range.     

Hyperfine Interactions of Pm in Nd and Gd Hosts

Time differential perturbed angular correlation measurements were carried out using short lived isomeric 5/2⁺ state in ¹⁴⁷Pm to investigate the magnetic and electric hyperfine interactions in Nd and Gd hosts at different temperatures. At 10 K the magnetic hyperfine fields at ¹⁴⁷Pm in Nd and Gd hosts are 361(42) kG and 256(30) kG, respectively, and are very low as compared to the free-ion value while the electric field gradients are of comparable order. The magnetic hyperfine field in Gd is constant with temperature. The results are interpreted in terms of singlet ground state of Pm ion. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Fields of Light Interstitial Impurities in Ni

The magnetic hyperfine interaction of light interstitial impurities in Ni have been studied by means of the Korringa–Kohn–Rostoker (KKR) band structure method. This method allows to deal with the impurity problem by solving the corresponding Dyson equation for the Green’s function. It also allows to account for lattice relaxations. For this purpose a new technique was developed that allows to handle in principle arbitrary lattice distortions. Corresponding calculations have been performed for the magnetic hyperfine fields of the light interstitial impurities H to Ne in Ni. By minimising the force on the nearest neighbour host atoms their equilibrium position was determined. The resulting hyperfine fields for the equilibrium configuration are found to be in rather good agreement with available experimental data.     

Coupled Rearrangement Channel Calculation of the Hyperfine Structure of the dtμ Molecule

Hyperfine structure splittings are calculated for the J = v = 1 state of the dtμ molecule. The splittings are determined by the accurate three-body wave function obtained by coupled rearrangement channel method using the updated physical constants. The result obtained is in good agreement with the previous calculation within ∼0.07 meV. The discrepancy is due to the accuracy of the three-body wave function. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hyperfine Fields of 181Ta in UFe4Al8

The γ–γ Perturbed Angular Correlation technique was used to study the hyperfine interaction of ¹⁸¹Ta at the Hf site(s) in UFe₄Al₈ at room temperature and 12 K. The data at room temperature are well described by two electric field gradients, while at low temperature two combined hyperfine interactions have to be considered, one with the magnetic hyperfine field collinear with the c-axis and another with the magnetic hyperfine field in the basal plane. The results are compared with previous Mössbauer and neutron diffraction experiments and the lattice site of Hf is discussed.

     

On the Use of a H2–O2 Gas Target in Muonic Hydrogen Atom Hyperfine Splitting Experiments

We propose a substantial improvement of the experimental method for the measurement of the hyperfine splitting of the ground state of muonic hydrogen described in earlier papers [1,2]. By further developing the idea to use the diffusion of the muon hydrogen atoms as a signature of laser-induced hyperfine transitions, we suggest a technique based on the energy dependence of the rate of muon transfer to oxygen in the thermal region, and demonstrate its efficiency and significant practical advantages. This revised version was published online in July 2006 with corrections to the Cover Date.     

周期磁场调制下的二维电子结构

基于有限差分方法,研究周期梯度磁场调制下二维电子气的电子性质.结果表明:由于周期梯度磁场的存在,体系展现出丰富的电子能带结构.其子带的宽度随|k_y|增大而不断变窄,|k_y|越大势阱越深;由于在k_y > 0和k_y < 0两个区域的有效势能不一样,其能带结构在两个区域不一致且在k_y > 0的区域中形成更多束缚态.通过改变磁条周期、磁条到2DEG的距离及磁化强度研究其对电子能带结构的影响.     

Hyperfine Interactions of 8Li in Ferromagnetic Single Crystal Fe

The hyperfine interactions of ⁸Li implanted in single crystal Fe have been studied using the β-NMR technique. One kind of hyperfine field B _hf was found. Since no dipolar field was observed, ⁸Li nuclei are suggested to sit in substitutional sites. The B _hf and the spin-lattice relaxation time T ₁ were observed as functions of temperature. The experimental B _hf and T ₁ were compared with the theoretical predictions from the first principles KKR-band-structure calculations. While predicted B _hf for the substitutional site is consistent with the experiment, predicted T ₁ cannot reproduce the experiment well. This revised version was published online in September 2006 with corrections to the Cover Date.     

Magnetic Properties and the Electric Field Gradients of Fe4N and Fe4C

The magnetic properties and the hyperfine interactions of Fe₄N and Fe₄C under high pressures are discussed on the basis of first-principles electronic structure calculations performed by the KKR Green's function method and its extention into a full potential scheme (FP-KKR). The results show that both Fe₄N and Fe₄C undergo a weak first order transition from high to low spin states under pressure. This transition is sensitively reflected not only by H _hf but also by EFG. The calculated Curie temperature, magnetic moments and H _hf well reproduce the experimental observations.