Nuclear hyperfine effects in Dy(OH)3

A crystal field analysis of the experimental data on magnetic, optical and thermal properties of Dy(OH)₃ single crystals have been published The nuclear hyperfine properties of Dy³⁺ in Dy(OH)₃ were studied using a crystal field thus obtained. The hyperfine spectra were computed from 4–20 K with a minimum number of approximations. Under a weak crystal field, the lowest electronic level is a Kramers' doublet For this highly anisotropic crystal, the magnetic hyperfine and the quadrupole interactions are both prominent The quadrupole interaction energy is temperature dependent The value of the magnetic Sternheimer factor R_hf/R is determined to be 0 14 The observed specific heat $\text{C}{}_{\mathrm{hf}}\text{R}$ arising from hyperfine interactions have been explained satisfactorily A maxima is expected at 21 mK.     

Observation of a long relaxation time of the hyperfine field of Dy and Er after recoil implantation in iron and derivation of g-factors of rotational states in 164Er and 164Dy

After heavy ion multiple Coulomb excitation of ^162,164Dy and ^164,166Er and recoil implantation in iron the integral rotations of \gamma--\gamma directional correlations in the static hyperfine field were measured for the 4₁ ⁺, 6₁ ⁺ and 8₁ ⁺ states. The targets were cooled by liquid nitrogen and magnetized in beam direction by an external magnetic field of ± 4.5 T. With the known g-factors of ¹⁶⁶Er (A. Alzner et al., Z. Phys. A 322 (1985) 467) and ¹⁶²Dy (I. Alfter et al., Z. Phys. A 357 (1997) 13) effective average hyperfine fields were derived. They are smaller than the equilibrium values known from Mössbauer experiments (H.P. Wit et al., Hyp. Interact. 5 (1978) 233; L. Niesen et al., Hyp. Interact. 3 (1977) 109) and increase with the mean lives of the states. A possible explanation of the observed slow relaxation may be the hindrance of exchange within the spin system by the antiferromagnetic coupling between impurity atom and host. The data obtained for ¹⁶⁴Er and ¹⁶⁴Dy were used to derive the g-factors: g(4₁ ⁺,¹⁶⁴Er) = +0.365(38), g(4₁ ⁺,¹⁶⁴Dy) = +0.251(31), and g(6₁ ⁺, ¹⁶⁴Dy) = +0.272(50).     

The magnetic hyperfine field at Cd nuclei in the rare earth ferromagnets Gd,Tb, Dy,Ho, Er and Tm

The time differential perturbed angular correlation technique has been used to study the combined magnetic and electric hyperfine interactions at the site of a¹¹¹Cd impurity in the rare earth ferromagnets Gd, Tb, Dy, Ho, Er, and Tm at 4.2 °K. The following magnetic hyperfine fields at the site of¹¹¹Cd have been found: ¦H _hf ¦=340(7) kG in Gd, 275 (5) kG in Tb, 221 (4) kG in Dy, 116 (3) kG in Er and 60 (6) kG in Tm. In Ho two magnetically different sites were observed with magnetic fields of 159 (3) and 139 (3) kG. Both sites are equally populated. The coupling constantJ _5f of the conduction electron-4f interaction has been calculated for the different rare earth metals from the measured hyperfine fields by means of the RKKY theory.     

NMR of Dy nuclei in ferromagnetic DyAl2 and Dy metal

The NMR spin echo of Dy nuclei in ferromagnetic DyAl₂ yields for the Dy¹⁶¹ hyperfine field constant, a=?845.2±0.3 MHz and quadrupolar splitting, 2P=420.0±0.3 MHz compared to a=?830.0±0.5 MHz and 2P= 387.8±0.5 MHz in ferromagnetic Dy metal. The different contributions to these parameters are discussed. A line, observed at 1273 MHz Dy metal, is attributed to Δm_I = 2 transition.     

Mössbauer studies of Dy2Fe17−yAly hydrides

The x-ray and Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₂Fe_17–y Al (y=0, 1,5 and 3) compounds and their hydrides are reported.Hydrogenation slightly increases the lattice parameters. An appreciable increase of the isomer shift and the hyperfine field at⁵⁷Fe nuclei is observed after hydrogenation. The hyperfine field for both the parent compound and its hydride decreases with increasing Al content across the series. Only a small variation of the hyperfine field at¹⁶¹Dy nuclei is noticeable after hydrogenation.     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Investigation of the impurity hyperfine field polarization in polycrystalline Rare Earth ferromagnets

Time differential perturbed angular correlation spectra of¹¹¹Cd in ferromagnetic polycrystalline Dy have been measured at 4.2 K in external magnetic fields up to 60 kG. The experimental data were well reproduced by a calculation which assumed that the angular distribution of the magnetic hyperfine fields is identical to that of the magnetic moments of the 4f-shells. The distribution of the 4f-moments was derived from magnetic anisotropy data. The results of this work seem to justify the application of the integral perturbed angular correlation technique for the determination of magnetic hyperfine fields in incompletely polarized ferromagnetic samples. The magnetic hyperfine fields of¹⁷⁷Hf:Gd and¹⁷⁷Hf:Dy have been measured by this method as:H _hf(Hf:Gd)=–375(60)kG andH _hf(Hf:Dy)=–225(45)kG.     

Anomalous hyperfine field and orbital moment of cobalt in RCo2; R = Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Tm

⁵⁹Co spin echo NMR spectra in the magnetically ordered phase of the MgCu₂ type RCo₂ compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo₂ with the easy direction of magnetication parallel to the 〈011〉 or 〈111〉 direction, the ⁵⁹Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the ⁵⁹Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb_1?xY_xCo₂. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.     

Investigation of the magnetic hyperfine field at197Au impurities in the heavy Rare Earth metals

The Mössbauer effect has been used to measure the magnetic hyperfine field at the site of¹⁹⁷Au impurities in the heavy Rare Earth metals Gd, Tb, Dy, Ho and Er at 4.2 K. The magnetic hyperfine field decreases in a non linear way with decreasing spin of the Rare Earth host. For¹⁹⁷Au this decrease is stronger than for any other impurity investigated up to now. Possible reasons for this behaviour are discussed.     

The temperature dependence of the magnetic hyperfine field of tantalum in dysprosium

The temperature dependence of the magnetic and electric hyperfine interactions at the site of ¹⁸¹Ta impurities in polycrystalline Dy has been measured between 4.2 and 178 K using the time differential perturbed angular correlation technique. The value of the magnetic hyperfine field at 4.2 K is: |H_hf(TaDy)| = 212(9) kG The temperature dependence of the magnetic hyperfine field follows closely the prediction of the molecular field model.     

Ratio ofg I -factors and hyperfine structure anomalies of99Ru and101Ru

The ratio of theg _I -factors of⁹⁹Ru and¹⁰¹Ru has been measured accurately by the nuclear magnetic resonance method. Using hyperfine interaction constants from literature, the hyperfine structure anomalies of some atomic states of ruthenium are obtained.     

The contribution of 5d electrons to the saturation magnetic moments and magnetic hyperfine fields in the heavy rare earth metals

The main results of a model for 5d electrons in the heavy rare earth metals are presented. The model involves the use of wave functions based on published analyses for 4fⁿ5d6s² atomic configurations, and the spreading of each of these energy levels uniformly over a band of width W in the metals. Excess saturation magnetic moments above those of the tripositive ions can be explained by the model with W in the range 0.84±0.16eV in the five metals Gd, Tb, Dy, Er and Tm. The magnetic hyperfine fields in the metals include negative contributions from the 5d electrons which have been shown to amount to about ?250koe in Gd, Er and Tm.     

A study of the magnetic moments and Fe site hyperfine fields in iron-chromium alloys

The magnetization of Fe-Cr alloys ranging from 1 to 15 atomic % of Cr has been measured at room temperature in order to study the relationship between the Fe site hyperfine fields and the magnetic moment. The average moment decreases linearly, at a rate of -2.36 μ_B per Cr atom, up to 10% Cr concentration. The Fe site hyperfine fields were measured in a previous study¹ using the same samples. It is found that the hyperfine fields measured are not proportional to the corresponding magnetic moments. The results are interpreted using a model previously developed for other binary alloys of iron².     

Isotope shift and hyperfine structure of the highly excited atomic uranium

The laser induced fluorescence method using atomic beam combined with Doppler-free two-photon absorption technique was applied for the measurement of isotope shifts and hyperfine structures of atomic uranium including ²³⁴U, ²³⁵U, ²³⁶U and ²³⁸U isotopes. The isotope shifts between ²³⁸U-²³⁴U, ²³⁸U-²³⁵U, ²³⁸U-²³⁶U, and the hyperfine structure of ²³⁵U were obtained in the high lying odd levels around 4 eV. Received 3 December 2001 / Received in final form 4 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: oba@analchem.tokai.jaeri.go.jp     

Coulomb excitation studies of 160Dy, 162Dy and 164Dy

Coulomb excitation measurements with ¹⁶O and ⁴He projectiles have been performed on ¹⁶⁰Dy, ¹⁶²Dy, and ¹⁶⁴Dy. The ground-state rotational bands up through the 8⁺ member were observed in the ¹⁶O experiments. The measured excitation probabilities yield B(E2; I → I ?2) values which are generally in agreement with the rotational predictions except for the 6⁺ → 4⁺ values. In each nucleus, probabilities for exciting the 2⁺, 4⁺, and 6⁺ members of the γ-vibrational band were measured and compared with calculated results. The B (E2; 0⁺ → 2⁺γ) values were measured in experiments involving ⁴He ions. The K^π = 2^? octupole band was observed in each nucleus in addition to 1^? bands in ¹⁶⁰Dy and ¹⁶²Dy. Excitation probabilities were analyzed in an attempt to extract B(E3) values.     

Study of combined magnetic and electric hyperfine interactions for cadmium in Dysprosium by time differential perturbed angular correlations

The combined magnetic and electric hyperfine interaction at the site of a¹¹¹Cd impurity in magnetically ordered Dysprosium has been investigated as a function of temperature by time differential perturbed angular correlation measurements. Three different phases have been found in metallic Dy with transition temperatures of 85 and 179 °K in agreement with the results of bulk material measurements. In the paramagnetic phase above 179 °K a pure electric quadrupole interaction has been observed. The various contributions to the electric fieldgradient are analyzed and it is shown, that the dominant contribution comes from the conduction electrons. In the ferromagnetic phase which extends from 0 to 85 °K the magnetic hyperfine field at the site of¹¹¹Cd has the same temperature dependence as the spontaneous magnetization. The value of the hyperfine field at 4.2 °K is ¦H _eff¦=(221 ± 4) kG. At 85 °K a transition to the antiferromagnetic phase of Dy occurs, which shows a hysteresis of the transition temperature. In the antiferromagnetic phase the temperature dependence of the hyperfine field deviates considerably from the magnetization curve. It is suggested that this deviation might be due to a temperature dependence of thes-f exchange interaction.     

Investigation of the hyperfine structure of electronic levels in chromium atom

Measurements of the hyperfine structure (hfs) of electronic levels of the chromium atom were performed using two spectroscopic methods. For 7 energy levels (3 even parity and 4 odd parity) the magnetic dipole and electric quadrupole hyperfine interaction constants A and B were determined for the first time. In this case the method of laser induced fluorescence (LIF) on an atomic beam was used. The low lying metastable levels belonging to the term 3d⁴4s² a⁵D were remeasured by the method of laser-rf double resonance on an atomic beam (ABMR-LIRF). To improve the accuracy of hyperfine splittings measurements, the stability of the radio frequnecy (rf) generator was increased by the use of a frequency standard synchronized by a GPS signal. The values of the hfs intervals for these levels were determined with the accuracy of a few kHz. The improvement in accuracy enabled an estimation of the octupole-coupling constant C.     

Anomalies in resonant absorption line profiles of atoms with large hyperfine splitting

We examine a monochromatic absorption line in the velocity-nonselective excitation of atoms when the components of the hyperfine stricture of the electronic ground states are optically pumped. We show that the absorption lines possess unusual substructures for some values of the hyperfine splitting of the ground state (which exceed the Doppler absorption linewidth severalfold). These substructures in the absorption spectrum are most apparent if the hyperfine structure of the excited electronic state is taken into account. We calculate the absorption spectra of monochromatic light near the D ₁ and D ₂ lines of atomic rubidium ^85,87Rb. With real hyperfine splitting taken into account, the D ₁ and D ₂ lines are modeled by 4-and 6-level diagrams, respectively. Finally, we show that atomic rubidium vapor can be successfully used to observe the spectral features experimentally. Zh. éksp. Teor. Fiz. 111, 93–106 (January 1997)     

Thallium hyperfine anomaly

Measurements of the hyperfine structure in the highly charged hydrogen like systems ²⁰³Tl⁸⁰⁺ and ²⁰⁵Tl⁸⁰⁺ are underway at the Super EBIT at LLNL. This work considers the effects of the nuclear magnetization distribution on the hyperfine structure. The difference in energy splitting due to hyperfine structure for ²⁰³Tl and ²⁰⁵Tl, respectively, is found to be 0.031 04(1) eV, which corresponds to a transition wavelength difference of 3.640(1) nm. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hyperfine interactions and crystal field effects in intermetallic compounds between Dy and 3d transition metals

A model based on the relative strengths of the magnetic exchange and electric field interactions is proposed for explaining the differences observed between the ¹⁶¹Dy Mössbauer spectrum of Dy₂Ni₁₇ where two dysprosium sites are observed and spectra of Dy₂Fe₁₇ and Dy₂Co₁₇ which show only one hyperfine pattern.