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The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science [1]. Twenty years after the first demonstration of isolated attosecond pulses [2], they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules and solids [3, 4]. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics [5, 6], surface science [7], and imaging [8]. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cut-off region of the XUV spectrum was already demonstrated in 2013 [9], the number of photons per pulse was insufficient to perform pulse characterisation via attosecond streaking [10], let alone to perform a pump-probe experiment. Here we report on the generation and full characterisation of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 106 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate one or two orders of magnitude above current implementations.

Many experiments in attosecond science will benefit from attosecond pulses at high repetition rates with sufficient photon flux for pump-probe experiments. We use 7fs, 800nm pulses from a non-collinear optical parametric chirped pulse amplification (NOPCPA) laser system to generate few-pulse attosecond pulse trains (APTs) in the extreme ultraviolet (XUV) at a repetition rate of 100kHz. The pulse trains have been fully characterized by recording FROG-CRAB (Frequency-Resolved Optical Gating for Complete Reconstruction of Attosecond Bursts) traces with a velocity map imaging spectrometer., Comment: 7 pages, 4 figures, submitted version

In this paper, a model based on the molecular field theory is used to fit experimental data of the magnetic hyperfine field (mhf) at nuclei of a magnetic dilute impurity in a magnetic host and determine separately the contributions of the host and the impurity to mhf, which otherwise would not be possible. The model is used to fit data on the temperature dependence of mhf at 140Ce nuclei as an impurity replacing rare-earth (RE) ions in REAg (RE = Gd, Tb, Dy, Ho) hosts. Experimental data on GdAg and DyAg are available in the literature and data on the temperature dependence of mhf for TbAg and HoAg were measured by perturbed gamma–gamma angular correlation (PAC) spectroscopy. Due to the magnetic interplay between host and impurity magnetic ions, the behavior of the temperature dependence of mhf below respective TN of each compound shows an accentuated deviation from an expected Brillouin-like pattern for each compound. This unusual behavior is a consequence of an additional magnetic interaction which emerges from the polarization of localized moments of Ce induced by the magnetic field from RE ions. The impurity contribution calculated from the model are shown to follow the same behavior of the reduced hyperfine field determined from experimental data. The host contribution is discussed in terms of the indirect magnetic coupling between the magnetic RE ions of the host and the obtained values are supported by first-principles calculations based on the density functional theory (DFT). It is also shown that both contributions calculated by the model have values within the expected experimental systematic. Moreover, density of states (DOS) from first-principles calculations explain the mechanism responsible by the observed anomalous behavior of the temperature dependence of mhf. The model presented here can be applied to understand the complex phenomenon of interactions between the magnetic ions of a ordered host and dilute magnetic impurity atoms. The physical description of these magnetic interactions might have an important impact to new applications in spintronics and quantum computing.

Hafnium oxide thin films with varying oxygen content were investigated with the goal of finding the optical signature of oxygen vacancies in the film structure. It was found that a reduction of oxygen content in the film leads to changes in both, structural and optical characteristics. Optical absorption spectroscopy, using nanoKelvin calorimetry, revealed an enhanced absorption in the near-ultraviolet (near-UV) and visible wavelength ranges for films with reduced oxygen content, which was attributed to mid-gap electronic states of oxygen vacancies. Absorption in the near-infrared was found to originate from structural defects other than oxygen vacancy. Luminescence generated by continuous-wave 355-nm laser excitation in e-beam films showed significant changes in the spectral profile with oxygen reduction and new band formation linked to oxygen vacancies. The luminescence from oxygen-vacancy states was found to have microsecond-scale lifetimes when compared with nanosecond-scale lifetimes of luminescence attributed to other structural film defects. Laser-damage testing using ultraviolet nanosecond and infrared femtosecond pulses showed a reduction of the damage threshold with increasing number of oxygen vacancies in hafnium oxide films.

The progress in the development of a high acquisition rate attosecond XUV-IR pump-probe beamline is discussed. A high repetition rate parametric amplifier allows driving the harmonic generation process at a repetition rate of 100 kHz.

This paper reports the investigation of the magnetic hyperfine field ${B}_{hf}$ in a series of rare-earth ($R$) cadmium intermetallic compounds $R\mathrm{Cd}$ and ${\mathrm{GdCd}}_{2}$ measured by perturbed angular correlation (PAC) spectroscopy using $^{111}\mathrm{In}/^{111}\mathrm{Cd}$ as probe nuclei at Cd sites as well as first-principles calculations of ${B}_{hf}$ at Cd sites in the studied compounds. Vapor--solid state reaction of $R$ metals with Cd vapor and the $^{111}\mathrm{In}$ radioisotope was found to be an appropriate route of doping rare-earth cadmium compounds with the PAC probe $^{111}\mathrm{In}/^{111}\mathrm{Cd}$. The observation that the hyperfine parameters depend on details of the sample preparation provides information on the phase preference of diffusing $^{111}\mathrm{In}$ in the rare-earth cadmium phase system. The $^{111}\mathrm{Cd}$ hyperfine field has been determined in the compounds $R\mathrm{Cd}$ for the $R$ constituents Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, in several cases as a function of temperature. For most $R$ constituents, the temperature dependence ${B}_{hf}(T)$ of $^{111}\mathrm{Cd}$:$R\mathrm{Cd}$ is consistent with ferromagnetic order of the compound. DyCd, however, presents a remarkable anomaly: a finite magnetic hyperfine field is observed only in the temperature interval 35 K $\ensuremath{\le} T \ensuremath{\le}$ 80 K which indicates a transition from ferromagnetic order to a spin arrangement where all $4f$-induced contributions to the magnetic hyperfine field at the Cd site cancel. First-principles calculation results for DyCd show that the ($\ensuremath{\pi}, \ensuremath{\pi}$, 0) antiferromagnetic configuration is energetically more favorable than the ferromagnetic. The approach used in the calculations to simulate the $R\mathrm{Cd}$ system successfully reproduces the experimental values of ${B}_{hf}$ at Cd sites and shows that the main contribution to ${B}_{hf}$ comes from the valence electron polarization. The de Gennes plot of the hyperfine field ${B}_{hf}$ of $^{111}\mathrm{Cd}$:$R\mathrm{Cd}$ vs the $4f$-spin projection $(g\ensuremath{-}1)J$ reflects a decrease of the strength of indirect $4f\ensuremath{-}4f$ exchange across the $R$ series. Possible mechanisms are discussed and the experimental results indicate that the indirect coupling is provided by the intra-atomic $4f\ensuremath{-}5d$ exchange and interatomic $5d\ensuremath{-}5d$ interaction between the spin-polarized $5d$ electrons of neighboring $R$ atoms. The ratio of the hyperfine fields of GdCd and ${\mathrm{GdCd}}_{2}$ scales with the number of nearest Gd neighbors. In the paramagnetic phases of the $R\mathrm{Cd}$ compounds, the PAC spectra indicate the presence of a broad distribution of weak quadrupole interactions suggesting a perturbation of the cubic CsCl symmetry of the Cd site, most probably due to chemical disorder of the $R$ and Cd sublattices. A substantial interchange of $R$ and Cd atoms is also reflected in the temperature dependence of the linewidth of the magnetic hyperfine interaction in the magnetically ordered phase of $R\mathrm{Cd}$ and ${\mathrm{GdCd}}_{2}$. Its critical increase towards the order temperature is evidence for a distribution of the order temperature with a width of about 10 K.

Magnetic and electric hyperfine interaction of the nuclear probe 111In/111Cd in intermetallic compounds of the rare earth-gallium system have been investigated by perturbed angular correlation (PAC) spectroscopy. The PAC measurements, supported by X-ray diffraction, provide evidence for a marked phase preference of 111In for hexagonal RGa2 over orthorhombic RGa and of RGa3 with the L12 structure over RGa2. In the case of SmGa2, the magnetic hyperfine field Bhf, the electric quadrupole interaction and the angle β between Bhf and the symmetry axis of the electric field gradient have been determined as a function of temperature. The angle β = 0 is consistent with the results of previous magnetization studies. Up to T ≤ 17 K the magnetic hyperfine field has a constant value of Bhf = 3.0(2) T. The rapid decrease at higher T gives the impression of a first-order transition with an order temperature of TN = 19.5 K. In the RKKY model of indirect 4f interaction the ratio TC/Bhf(0) is a measure of the coupling constant. For 111Cd:SmGa2 (TC/Bhf(0)~6.5 K/T) this ratio is significantly smaller than for the same probe in other R intermetallics (SmAl2 ~9.5 K/T, Sm2In ~13.5 K/T).

The hyperfine field at 181Ta lattice sites in a nanostructured HfO2 thin film doped with Fe was studied using Rutherford Backscattering Spectrometry and Perturbed Angular Correlation techniques. The 409 nm Hf film was deposited by Electron Beam Evaporation on a silicon substrate. The radioactive 181Hf ions were produced by neutron activation of the nanofilm in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n,γ)181Hf. These studies provided an excellent opportunity to obtain unique information regarding local arrangement of the grains, structure, phase transformations of nanoparticles and interfaces of nanostructured materials and the thin film.

Hafnium oxide thin films with varying oxygen content were investigated with the goal of finding the optical signature of oxygen vacancies in the film structure. It was found that a reduction of oxygen content in the film leads to changes in both, structural and optical characteristics. Optical absorption spectroscopy, using nanoKelvin calorimetry, revealed an enhanced absorption in the near-ultraviolet (near-UV) and visible wavelength ranges for films with reduced oxygen content, which was attributed to mid-gap electronic states of oxygen vacancies. Absorption in the near-infrared was found to originate from structural defects other than oxygen vacancy. Luminescence generated by continuous-wave 355-nm laser excitation in e-beam films showed significant changes in the spectral profile with oxygen reduction and new band formation linked to oxygen vacancies. The luminescence from oxygen-vacancy states was found to have microsecond-scale lifetimes when compared with nanosecond-scale lifetimes of luminescence attributed to other structural film defects. Laser-damage testing using ultraviolet nanosecond and infrared femtosecond pulses showed a reduction of the damage threshold with increasing number of oxygen vacancies in hafnium oxide films.

The hyperfine field at 181Ta lattice sites in nanostructured HfO2 thin films was studied by the Perturbed Angular Correlation (PAC) technique. Thin oxide films were deposited by Electron Beam Evaporation on a silicon substrate. The thickness of the films was ~100 nm and ~250 nm. Radioactive 181Hf nuclei were produced by neutron activation of the film samples in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n,γ)181Hf. PAC measurements were carried out after annealing at 1473 K. The PAC technique allows the determination of the electric field gradient (EFG) at the probe sites.

In this work the perturbed angular correlation technique is used to locally monitor the epitaxy and thermal stability of the hafnium layer in a Zr/Hf/Zr multilayer. The studies reveal that the system is highly homogeneous and presents high epitaxy. Measurements at high temperatures show that no HfOx formation occurs up to 562 K but at this temperature the Hf layer is no longer oxygen-defect free.

The magnetic hyperfine field ( B hf ) at Nd sites in NdAg was investigated experimentally by perturbed gamma–gamma angular correlation technique using 140 La– 140 Ce probe nuclei and by first-principles electronic structure calculations. The temperature dependence of the observed B hf shows a sharp deviation from an expected Brillouin-like behavior. This behavior is believed to result from an additional magnetic interaction from the polarization of Ce spin moments induced by an exchange interaction between Ce and Nd ions. The experimental results for the temperature dependence of B hf have been fitted by using a model based on the molecular field theory. The results are discussed in terms of a competition between the RKKY interaction and the 5d–5d interaction for the indirect magnetic coupling between the magnetic Nd ions.

In the present work, the time differential perturbed angular correlation (PAC) technique was used to study the temperature dependence of electric field gradient (efg) in GdCoO 3 perovskite using 111 Cd and 181 Ta nuclear probes. The radioactive parent nuclei 111 In and 181 Hf were introduced in the oxide lattice through chemical process during sample preparation and were found to occupy only the Co sites in GdCoO 3 . The efg's at 111 Cd and 181 Ta show temperature dependence with two different fractions each that change with temperature. In the case of 111 Cd the quadrupole frequency slowly decreases, with corresponding increase of the temperature and shows a peak like structure at around 200 K and a discontinuity at 700 K. These changes have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin state and from intermediate-spin to high-spin state of Co 3 + ion similar to LaCoO 3 compound. Indication of a Jahn–Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.

The hyperfine field at 181Ta lattice sites in a nanostructured Hf02 thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive 181Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction 180Hf(n,γ)181Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the 181Ta probe sites. The 181Ta isotopes appear in the sample as disintegration product of 181 Hf.

The local magnetic interaction at the transition metal sites in RMO3 (R=La, Nd; M=Cr, Fe) compounds has been investigated by perturbed angular correlation (PAC) technique using 181Hf→181Ta probe nuclei. The present measurements cover a temperature range from 10 K to 1000 K. Above the respective Neel temperature, each compound shows a unique quadrupolar frequency that decreases linearly with temperature. These interactions were assigned to the radioactive probe substituting Cr or Fe sites. Below TN, a combined electric plus magnetic hyperfine interaction was observed. The magnetic interaction revealed that the super transferred hyperfine fields on 181Ta at the Cr sites in (La,Nd)CrO3 extrapolated to 0 K, are much smaller than the corresponding values at Fe sites in (La,Nd)FeO3. This difference was attributed to different distribution of d electrons in Cr3+ (3d3) and Fe3+ (3d5) ions in each compound. As the fields for Nd compounds are smaller than those for La compounds, the role of rare-earth ions in the magnetism of these oxides is also discussed.

The temperature dependence of the electric field gradient (efg) in TbCoO3 perovskite was measured by perturbed angular correlation (PAC) technique using 111Cd and181Ta nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced into the compound through a chemical process during sample preparation. The electric quadrupole interactions at 111Cd show two different sites, assigned to probe substituting Tb and Co atoms. The temperature dependence of quadrupole frequencies show sharp discontinuities which have been interpreted as thermally activated spin state transitions from low-spin ground state configuration to the intermediate-spin state and from intermediate-spin to high-spin state of Co3 + ion. For 181Ta only one interaction was observed, which was assigned to probe at Co site. Indication of a Jahn–Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out. No magnetic order was observed till 77 K.

This work had the objective to determine the Hydraulic Conductivity K(theta) function for different depth levels z, of columns of undisturbed soil, using the gamma ray transmission technique applied to the Sisson method. The results indicated a growing behavior for K(theta) and a homogeneous soil density, both in relation to the increase of the depth. The methodology of gamma ray transmission showed satisfactory results on the determination of the hydraulic conductivity in columns of undisturbed soil, besides being very reliable and a nondestructive method.O estudo da condutividade hidráulica para solos não saturados é essencial quando aplicado às situações relacionadas à irrigação, drenagem e transporte de nutrientes no solo, é uma importante propriedade para desenvolvimentos de culturas agrícolas. Este trabalho tem o objetivo de determinar a função Condutividade Hidráulica K(teta), em diferentes níveis z de profundidade, em colunas de solo indeformado, utilizando a transmissão de raios gama aplicada ao método de Sisson. Os resultados indicam um comportamento crescente para K(teta) e uma densidade de solo homogênea, ambos em relação ao aumento da profundidade. A metodologia de transmissão de raios gama mostrou resultados bastante satisfatórios na determinação da condutividade hidráulica em colunas de solo indeformado, além de ser muito confiável e não destrutivo.

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.

In this paper, the effect in structural and magnetic properties of iron doping with concentration of 20% in hafnium dioxide (HfO2) nanoparticles is investigated. HfO2 is a wide band gap oxide with great potential to be used as high-permittivity gate dielectrics, which can be improved by doping. Nanoparticle samples were prepared by sol-gel chemical method and had their structure, morphology, and magnetic properties, respectively, investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD), and magnetization measurements. TEM and SEM results show size distribution of particles in the range from 30 nm to 40 nm with small dispersion. Magnetization measurements show the blocking temperature at around 90 K with a strong paramagnetic contribution. XRD results show a major tetragonal phase (94%).

The magnetic hyperfine field (mhf) at Dy sites in DyAg and DyCu was investigated with perturbed gamma–gamma angular correlation technique using 140 La– 140 Ce probe nuclei. The temperature dependence of the observed mhf shows a deviation from an expected Brillouin-like behavior with a sharp increase of mhf values for temperatures below approximately half of T N for each compound. This additional magnetic interaction is believed to result from the polarization of Ce spin moments induced by the magnetic field from Dy atoms. The experimental results for the temperature dependence of mhf are fitted by using a model based in the molecular field theory. The results are discussed in terms of the RKKY model for the indirect magnetic coupling between the magnetic Dy ions.

Fil: Forker, M.. Centro Brasileiro de Pesquisas Fisicas; Brasil. Ministerio da Ciencia, Tecnologia e Inovacoes; Brasil

The magnetic behavior of Gd2O3 nanoparticles, produced by thermal decomposition method and subsequently annealed at different temperatures, was investigated by magnetization measurements and, at an atomic level, by perturbed γ − γ angular correlation (PAC) spectroscopy measuring hyperfine interactions at 111In(111Cd) probe nuclei. Nanoparticle structure, size and shape were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Magnetization measurements were carried out to characterize the paramagnetic behavior of the samples. XRD results show that all samples crystallize in the cubic-C form of the bixbyite structure with space group Ia3. TEM images showed that particles annealed at 873 K present particles with highly homogeneous sizes in the range from 5 nm to 10 nm and those annealed at 1273 K show particles with quite different sizes from 5 nm to 100 nm, with a wide size distribution. PAC and magnetization results show that samples annealed at 873 and 1273 K are paramagnetic. Magnetization measurements show no indication of blocking temperatures for all samples down to 2 K and the presence of antiferromagnetic correlations.

This paper presents the first results of an innovative solid-state Marx type modulator connected to a Plasma Based Ion Implantation (PBII) system. The PBII system has two main objectives; support surface engineering research and assist the development of new pulsed power modulators for plasma applications. The results of preliminary tests done in nitrogen gas atmosphere, with 1011 cm−3 ion density and 0.1 Pa pressure are discussed. About 25 µs width, 1 kHz negative pulses, of ∼10 kV negative amplitude, were applied to a metallic cylinder (100 mm × 10 mm) vertically placed on it, drawing 6 A peak current. The modulator limits the plasma short-circuit up to 100 A per pulse.

Anderson Camargo Moreira1*, Otavio Portezan Filho2, Fabio Henrique de Moraes Cavalcante3 and Carlos Roberto Appoloni2 1Programa de Pos Graduacao em Ciencias e Engenharia de Materiais/EMC, Universidade Federal de Santa Catarina – UFSC, 2Depto. de Fisica, Universidade Estadual de Londrina – UEL, 3Centro de Fisica Nuclear, Instituto Superior de Engenharia/DEEA/ISEL, Universidade de Lisboa, 1,2Brasil 3Portugal

The magnetic and electric hyperfine interactions of the nuclear probe Cd111 in the hexagonal antiferromagnetic rare earth-gallium RGa2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) intermetallic compounds have been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature. With the exception of R = Nd and Ho, the magnetic hyperfine field Bhf is roughly proportional to the spin projection (g − 1)J of the R constituent. However, in the group of the light rare earths, the variation of Bhf with (g − 1)J is much weaker than that for the heavy R constituents, in contrast to the trend reported for all rare earth intermetallics investigated up to now as well as to the trend of the magnetic ordering temperatures of RGa2. The orientation of the 4f spins relative to the c axis of RGa2 deduced from the angle between Bhf and the symmetry axis of the electric field gradient was found to be temperature independent and in agreement with the results of previous magnetization measurements...

Hyperfine interactions in perovskite-structure RCoO3 (R=Gd,Tb) compounds have been measured by perturbed angular correlation technique using Cd111 and Ta181 nuclear probes. The electric quadrupole interactions at Cd111 show two different sites, assigned to probe substituting Gd or Tb and Co atoms. The temperature dependence of quadrupole frequencies shows discontinuities which have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin (IS) state and from IS state to high-spin state of Co3+ ion. For Ta181 only one major interaction was observed, which was assigned to probe at Co sites. Indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.