New aspect in transient magnetic fields using heavy ion beams

Transient field precessions have been measured with the first excited 2 ₁ ⁺ -state as probe for ions of²⁸Si traversing Fe at v_ion?1v₀ and 13v₀(v₀=c/137) and⁶²Ni being stopped in Fe. The degree of polarization deduced for the Si ions, p_1s=0.19(6), is consistent with low-velocity data. There is clear evidence that the field strength is attenuated by heavy ion beams. For the⁶²Ni(2 ₁ ⁺ ) state at 1.173 MeV a g-factor value of g=0.34(7) was obtained in good agreement with a previous result.     

Light nuclei as distinct probes for transient magnetic fields

Salient features of transient magnetic fields are brought out from nuclear spin precession measurements on light ions penetrating polarized Fe-, Ni- and Gd-hosts. At low velocities ion fractions with singleK-shell vacancies, at high velocities H-like charge state fractions, can account for the observed precessions. The data suggest a sharp reduction of theK-shell field at a velocityv _ion?0.5v ₀. Large degrees ofK-shell polarization have been derived for C- and O-ions. Measurements in different ferromagnets show that the transient fields scale with the polarized electron density of the host.     

The g-factor of the first excited 2+ state in 26Mg from transient field precession measurements

Transient field (TF) precessions of the first excited 2⁺ state in ^24,26Mg have yielded g = +0.50 (13) for ²⁶Mg. Contrary to an earlier measurement the present data is in good agreement with Hartree-Fock calculations. The large effective TF of 280 (30) T at Mg nuclei for ν_ion ≈ 2.0 ν₀ is attributed to K-shell polarization of the ions.     

Measurements of transient magnetic fields on single-electron Ni-ions

Measurements were performed to determine the transient magnetic field assoclated with polarized is electrons of highly-stripped Ni ions traversing a ferromagnetic Fe layer. Partiele γ angular correlations and spin precessions have been measured with the first excited 2^↓-state in⁶²Ni. The observed precession indicates that the transient field is considerabls weaker than expected.     

Disparity between the transient hyperfine fields for Pt and Os in Fe; an electron vacancy sharing interpretation

Precessions of the 2 ₁ ⁺ states in¹⁹⁸Pt and¹⁹²Os have been measured in the enhanced transient hyperfine magnetic field acting on these nuclei as they recoiled through thin polarized cobalt foils. Two separate targets consisting of contiguous layers of¹⁹⁸Pt and¹⁹²Os electrodeposited on ～1 μm and ～4 μm Co foils were employed. The levels of interest were Coulomb excited by 80 MeV³²S and 220 MeV⁵⁸Ni beams and the precessions of the 2 ₁ ⁺ →0 ₁ ⁺ γ-ray angular distributions in both nuclides were measured simultaneously. The results of these studies are compared with recently reported similar studies in which ions of¹⁸⁸Os and¹⁹⁴Pt recoiled through thin polarized Fe foils. It is concluded that (i) the transient field acting on Pt in Fe is singularly anomalous, and (ii) the recent contention that the g-factors of the 2 ₁ ⁺ states in the event Pt isotopes may be substantially lower than had been reported in the literature cannot be sustained. This transient field discontinuity is examined in terms of possible molecular orbital electron vacancy sharing between Pt and Fe.     

Disparity in transient field characteristics for Au ions traversing Fe and Gd hosts through measurements ofg-factors in197Au

Transient field precessions were measured for levels in the nuclides of^182,184,186W and¹⁹⁷Au as their ions simultaneously traversed polarized Fe and Gd hosts. Consistent sets of gyromagnetic ratios were inferred for the lowest 5/2⁺ and 7/2⁺ states in¹⁹⁷Au using these two ferromagnetic host media, provided that (i) the transient field for Au ions in Gd is calibrated using the W in Gd precessions (simultaneously measured) and, (ii) the transient field for Au in Fe is calibrated using the field strength and velocity dependence for Pt in Fe (previously measured). The presentg-factor results are: g(5/2 ₁ ⁺ ;¹⁹⁷Au)=0.296±0.023, g(7/2 ₁ ⁺ ;¹⁹⁷Au)=0.241±0.021, and g(5/2 ₁ ⁺ ;¹⁹⁷Au)=1.2±0.2.     

Formation of two ripple modes on Si by ion erosion with simultaneous Fe incorporation

This report focuses on the self organized nanostructure formation on Si (0 0 1) by erosion with low energy Kr⁺ ions with simultaneous incorporation of metallic atoms, in particular Fe. The incorporation of Fe is thought to play an important role in the formation of some features. In the experimental set-up used here the Fe atoms come from the sputtering of a cylindrical stainless steel target situated between the source and the sample holder. It is demonstrated how the Fe flux can be regulated by operational parameters of the ion source. It is shown that two different ripple modes, one perpendicular to the ion beam projection on the surface and the other parallel, were formed at near normal incidence (α = 20°) with ion energy between 300 eV and 2000 eV and a fluence of 6.7 × 10¹⁸ cm⁻². The perpendicular mode ripples dominated the topography when E_ion = 2000 eV, while the parallel mode ripples were the main features observed when E_ion = 300 eV. The correlation of Fe concentration with ion sources parameters and resulting topography is analyzed. It is demonstrated that a certain Fe concentration is necessary for the formation of ripples that are oriented perpendicular to the ion beam and that the Fe concentration alone does not determine the evolving topography.     

Can projectiles traversing solids bind electrons at all velocities?

PAC measurements on the 4.43 MeV ¹²C(2⁺) state on recoil in magnetized iron at velocities υ_ion = 0.058c, 0.071c yield integral nuclear precession angles of Φ = ?0.18 (30), +0.17 (39) mrad respectively. Evidently, the high electron-spin-polarization transfer to the innermost carbon orbits implied by a previous measurement (υ_ion = 0.03c, Φ = +0.85 (14) mrad) is suppressed at higher ion velocities.     

Optical Stark effects in the stimulated Raman spectrum of molecular oxygen

High-resolution stimulated Raman spectroscopy has been used to observe optical Stark effects in pure-spin, rotational, and rotational-vibrational transitions in molecular oxygen (X³Σ_g^?). Recorded spectra in both polarized and depolarized configurations demonstrate some striking differences in the Stark splitting of ³Σ ground state molecules from that reported previously for ¹Σ molecules. An analysis of the position of a number of normal and satellite rotational-vibrational lines in both the polarized and depolarized spectra has led to a measurement of a value for the v = 1 excited state polarizability anisotropy and to a more accurate value for the band origin of the v = 1 ← 0 transition: γ₁ = (α_| ? α_|)₁ = (1.36 ± 0.17) × 10^?24 cm³, and ν₀ = 1556.385 ± 0.001 cm^?1.     

Large transient magnetic fields at high ion velocities in polarized iron

Nuclear spin precessions due to the transient magnetic field in polarized Fe have been measured as a function of the initial velocity of²⁸Si ions in the first-excited nuclear state. The transient field was found to increase linearly with the ion velocityv in the regionv/c=0.006–0.049. This is in contrast to the Lindhard and Winther model, which requires an inverse proportionality with ion velocity. Reanalysis of an earlier measurement on³⁰Si(2 ₁ ⁺ ) with the linear velocity dependence yields a reduced value for theg-factor ofg=0.37±0.12. Other available velocity-dependent data for²²Ne,⁵⁶Fe and¹⁹⁶Pt are consistent with a linear velocity dependence and suggest in addition a linear dependence on the nuclear charge Z of the moving ion. The increase of the transient field with recoil velocity can be explained semi-quantitatively by the capture of polarized Fe electrons into 1s and 2s vacancies in the moving ion. The velocity-dependent data and other discrepancies from the Lindhard and Winther model for¹⁶N,¹⁸O and very recently, for¹²C are also discussed in terms of the proposed microscopic model.     

Magnetic-field and temperature effects on the optical properties of dicyano-2,2′-bipyridyl-platinum(II) single crystals

Studies of the polarized emission of [Pt(CN)₂(bipy)] single crystals as function of temperature (1.9 K ⩽ T ⩽ 295 K) and homogeneous magnetic fields (0 ⩽ H ⩽ 6 T), and the temperature dependence of the polarized absorption spectrum are reported. Raising the temperature from 1.9 to 7 K or increasing the magnetic field from 0 to 1 T results in a blue shift of ≈175 cm^-1 in the E ⊥ a polarized emission (E: electric field vector, a: crystallographic a axis). Between 1.9 and 295 K at H = 0) and between 0 and 6 T (at T = 1.9 K), the emission lifetime decreases by factors of ≈10³ and ≈10², respectively. The results are explained within the C'_2v symmetry of the single complex assuming a coupling between neighboring central ions.     

Ion-electron coincidence study of the thermal He(23S) + H2 Penning reaction

A new Penning-electron-Penning-ion coincidence method is described. It is applied to the study of the thermal reaction of He(2³S) with H₂. The main results reported are separate electron energy spectra that are coincident with the three different ions formed: HeH₂⁺, HeH⁺ and H₂⁺. Based on these results it is shown that the Penning reaction of the He(2³S)/H ₂ system proceeds in two well-separated steps: (i) ionization at distances R (HeH₂) ? 6a₀ in which H₂⁺ (v) is formed in different vibrational states; and (ii) reactive collision of H₂⁺ (v) with He. For the second step the variation of the branching ratios with vibrational quantum numbers v = 0 to v = 10 is derived, and it is shown that these branching ratios may be regarded as relative vibrational-energy-dependent cross-sections for the collision of H₂⁺ (v) with He at an average relative kinetic energy of ～20 meV.     

Magnetic anisotropy in multilayers

Magnetic anisotropy between in-plane and out of plane magnetic alignments is studied in a variety of multilayer systems using Mössbauer spectrosopy to observe the (Fe) magnetic orientation. The surface anisotropy in Fe/Au (1 1 1) multilayers is measured as K _s = 0.9 × 10^?3 Jm^?2. In Fe/Ni multilayers the dependence of magnetic orientation on external field applied normal to the layers enables volume and interface anisotropies K _v = (?5 ± 1) × 10⁴ Jm^?3 and K _s = (?0.6 ± 0.4)× 10^?3 Jm^?2 to be evaluated. In similar applied field experiments coherent rotation of the magnetic Fe and NiFe layers in Fe/Cu/NiFe/Cu multilayers was observed for intervening Cu layer thickness x = 5 Å but independent rotation for x = 50 Å. Out of plane magnetic components are observed for DyFe₂, YFe₂ thin films and DyFe₂/YFe₂ multilayers. In fields of up to 0.25 T applied inplane only the moments of the YFe₂ film showed significant rotation.     

Formation and growth mechanisms of ion-induced iron-carbon nanocomposites at room temperature

The irradiation of graphite surfaces with a simultaneous Fe supply have resulted into the development of various types of carbon nanocomposites. Their morphologies - diameter, density, length and apex angle strongly depend on the ratios of Fe deposition rate (D_Fe) to ion sputtering rate (S_ion). By optimizing the ratio of D_Fe/S_ion (2.40%), the denser and well-aligned Fe-carbon nanocomposite fibers (Fe-CNFs) could be obtained, whose average length and diameter were 0.95 μm and 17 nm, respectively. As confirmed by energy-dispersive X-ray analysis, the Fe-CNFs with amorphous-like or fine-polycrystalline phase were surely composed of carbon and Fe. Two types of growth models have been employed to explain the formation of metal-carbon nanocomposites.     

Scattering of polarized protons by iron and nickel isotopes

Elastic and inelastic scattering of polarized protons (E = 17.2, 20.4, 24.6 MeV) by ^{54, 56}Fe and ^{58, 60, 62} Ni have been investigated. Most data can be readily accommodated by standard optical-model and DWBA procedures, including full Thomas coupling. The 2⁺₁ state (1.41 MeV) in ⁵⁴Fe is peculiar because the inelastic scattering data require deformation parameters for the central and spin-orbit parts of the nuclear potential that differ by a factor 2 to 3; moreover, this anomaly shows a marked energy dependence.     

Thermal neutron induced charged particle reactions on58,59,61Ni

The thermal neutron induced charged particle spectroscopy on^{58, 59, 61}Ni (target nuclei) was done at the 87 m thermal neutron curved guide of the Grenoble high flux reactor. In the⁵⁹Nu(n, α)⁵⁶Fe reaction two lines showed up corresponding toα-particle transitions to the ground and first excited states in⁵⁶Fe with σ_α0=13.1±1.1 b and σ_α1 =0.188±0.01 b. A value of σ_γα≦13 mb was obtained for the two-step⁵⁹Ni(n, γα)⁵⁶Fe reaction. The technique to unfold theγα-spectrum and to get information on the primary low energyγ-rays is given and the present and our previous data on the¹⁴³Nd(n, γα)¹⁴⁰Ce reaction are analysed. For the⁵⁹Ni(n, p)⁵⁹Co reaction _p0=1.34±0.18b,σ _p1<0.30 b were determined. The cross-sections for the⁵⁸Ni(n,α)⁵⁵Fe and⁶¹Ni(n,α)⁵⁸Fe reactions were σ_α0≦30 Μb and σ_α0≦30 Μb respectively; these andσ _p1upper limit value are about 20–1500 times lower than the existing data. The other results are compared with the existing data and the differences are explained. The experimental data are compared with the values obtained from the statistical model.     

Electron work function in YNi3 − x T x (T = Cu,Fe, Mn; x = 0, 0.5) intermetallics

The electron work function in cast samples and cylindrical compacts of YNi_{3 ? x} T _x (T = Cu, Fe, Mn; x = 0, 0.5) intermetallics is determined using the contact potential difference method. A correlation is found between the electron work function and the electronegativity of elements substituting Ni in the YNi₃ structure.     

Graphite nanosheets doped with Fe, Ni, and N, synthesized in one step, and their unique magnetic performance

Graphite nanosheets (GNs) doped with N, Fe, or Ni were synthesized by pyrolysis of metal tetrapyridinoporphyrazine (MPTpz, M=Fe²⁺, and Ni²⁺) and a mixture of MPTpzs in a chemical vapor deposition furnace. The products obtained were characterized by scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy. The magnetic properties of the GNs obtained were investigated at room temperature using a vibrating sample magnetometer with an applied field of −10 000-10 000 Gs. The results show the GNs obtained are terrace-like and ultra-thin, with very high aspect ratio. Fe, Ni and N atoms have been doped to the GNs successfully. There are two types of N atom that are introduced into pure carbon systems: pyrinidic and graphitic N atoms. The GNs obtained exhibit ferromagnetic behavior at room temperature. Sample S1, obtained by pyrolysis of a mixture of MPTpzs (M=Fe²⁺ and Ni²⁺), have the highest coercivity force. The saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) values of sample S1 are 24.51 emu g⁻¹, 3.95 emu g⁻¹, and 207.34 Gs, respectively.     

Rate coefficient and transition probability of XeO

Rate coefficients of XeO(¹S) at various vibrational levels (v = 0, 1 and 2) were observed by measuring absolute intensities of the spectrum in the low-pressure d.c. glow of an Xe-O₂ mixture discharge. The association coefficients at the various levels are K_a0 = 2.4×10^-34 cm⁶ at v = 0, K_a1 = 1.1 × 10^-34 cm⁶ atv = 1, and K_a2 = 9.1 × 10^-35 cm⁶ at v = 2. The transition probability from XeO(¹S)₀ to $\text{XeO(}{}^1\text{D)u}$ is estimated to be A₀ = 1.3 × 10⁵ sec^-1.     

High-resolution infrared and microwave spectroscopy of the ν4 and 2ν2 bands of 14NH3 and 15NH3

More than two thousand Stark resonances of the ν₄ and 2ν₂ band transitions of ¹⁴NH₃ and ¹⁵NH₃ were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on ¹⁵NH₃ is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v₄ = 1 excited vibrational state of ¹⁴NH₃ and ¹⁵NH₃. Accuracies of all available spectroscopic data on the v₄ = 1 and the v₂ = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v₄ = 1 a (antisymmetric level) and v₂ = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v₄ = 1 a and the v₂ = 1 s states and between the v₂ = 2 s and the v₂ = v₄ = 1 a states (i.e., (v₁, v₂, v′₃, v′₄) = (0 1 0⁰ 1¹)) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10^?6. The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm^?1.