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1

Oxygen Emissions from Single-Crystalline Fe_3O_4 Surfaces Induced by Low-Energy Ion Bombardments

100%

Kim-Ngan N., Soszka W.

Acta Physica Polonica A

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2006

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vol. 109

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issue 6

715-721

EN

Negative-charged ion energy spectra of the Fe_3O_4 (001) and (111) surface revealed large peaks attributed to the O^- recoils from a binary collision. Under Ar^+ ion bombardments such an emission was largely affected by the screening effect of the Fe ions. A distinguished peak related to the O^+ recoil ions was observed under Ne^+ ion bombardments, while such a peak was merged into the high background in the case of Ar^+ ion ones. A weak effect from the Verwey transition was found on oxygen emissions. For the (111) surface a small peak characteristic of the O^+ recoils from double collisions appeared in the energy spectra around 140-170 K and a minimum was observed in both R^+(T) and R^-(T) curves under 6 keV Ne^+ ion beam.

2

Scanning Tunneling Spectra and Low Energy Ion Scattering Studies of the Verwey Transition in MBE Fe_3O_4 (100) Thin Film

81%

Kim-Ngan N., Soszka W., Hietschold M.

Acta Physica Polonica A

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2001

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vol. 99

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issue 2

267-276

EN

The (100) surface of magnetite Fe_3O_4 thin film was studied by a UHV low-temperature scanning tunneling microscope and by an ion scattering spectroscopy. The tunneling spectra revealed a widening of the gap with decreasing temperature, which may be related to the metal-insulator phase transition in this material. A strong effect of this phase transition on ion scattering from such a surface was observed. The temperature dependence of the scattered ion yield, R^+(T), revealed two minima at around 100 K and at 125 K under Ne^+ bombardment with the primary energy up to 6 keV. The disappearance of the high-temperature minimum at a bombarding energy of 6.5 keV gave a further evidence for the ion velocity dependence of the character of the R^+(T) curve, which has been first observed for a MBE Fe_3O_4 (111) film surface.

3

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

71%

Tarnawski Z., Kim-Ngan N., Wang X., Duijn V., Franse J.

Acta Physica Polonica A

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1998

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vol. 93

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issue 3

513-522

EN

The low-temperature specific-heat C(T) data of high-T_{c} superconductors RBa_{2}Cu_{3}O_{7-x}(R123O_{7-x}) were reviewed. A discussion of the C(T) data obtained on single-crystalline samples of Er123O_{7-x} and Sm123O_{7-x} compounds in applied magnetic fields for better evaluation of the crystal-electric-field parameters is given. The C(T) measurements of Sr-substituted compounds RBaSrCu_{3}O_{7} revealed the λ-type of peak related to the antiferromagnetic order at 1.2 K and 0.6 K respectively for Dy- and Er-compounds. The magnetic singlet ground state in these compounds is produced by weak exchange interactions of -0.05 T/μ_{B} and -0.035 T/μ_{B}, respectively. For Nd- and Sm-compounds, only a broad anomaly around 0.6 K was observed which is well fitted with a Schottky-type anomaly with an energy splitting of 1.4 K.

4

Surface Investigations of Selected Materials by Low-Energy Ion Scattering Technique

71%

Goc-Jagło D., Sitko D., Jagło G., Kim-Ngan N., Soszka W.

Acta Physica Polonica A

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2007

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vol. 111

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issue 5

763-771

EN

Surfaces of three selected materials were investigated by means of low-energy ion-scattering technique: (1) the magnetite (Fe_3O_4) exhibiting the so-called Verwey transition (T_V(bulk)=125 K) accompanied by a small cubic-monoclinic crystal distortion, (2) the intermetallic compound NdMn_2 undergoing an antiferromagnetic-paramagnetic phase transition (T_N=104 K) accompanied by a large crystal distortion with a volume change of 1%, and (3) the typical insulator BaTiO_3 with two structural transitions below 300 K. The primary energy of the (Ne^+, Ar^+) ion beam was in the range of 4-8 keV, and the low-energy ion-scattering spectra were collected in the temperature range of 85-300 K. A large influence from the Verwey transition on the neutralization and re-ionization of scattered ions from magnetite surface was observed, while no visible change at the magnetic phase transition in NdMn_2 was revealed in the low-energy ion-scattering spectra. A strong dependence of the characteristics of the low-energy ion-scattering spectra on the irradiated time was observed for BaTiO_3 indicating that this surface was heavily charged by ion bombardments.

5

Interface Properties of Single and Bi-Layer Fe_3O_4 Films Grown on MgO(001) Studied by RBS and Channeling Experiments

71%

Kim-Ngan N., Balogh A., Brötz J., Zając M., Korecki J.

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issue 4

570-575

EN

Series of Fe_3O_4/MgO(001) and Fe_3O_4/Fe/MgO(001) films (single- and bi-layer films, respectively) with a total layer thickness in the range of 20 ÷ 150 nm were investigated by the Rutherford backscattering spectrometry (2 MeV He^{+} ion beam), by the Rutherford backscattering spectrometry channeling experiments (1.5 MeV He^{+} ion beam). Depending on the layer thickness of each layer and the film geometry, a single Fe peak and/or a double-anomaly feature was revealed in the Rutherford backscattering spectra. For all films no magnesium presence in the surface layer was observed. For both single- and bi-layer films with a total layer thickness less than 60 nm only one minimum was observed in the channeling curves, while a double minimum was revealed for the bi-layer films with a larger thickness. X-ray reflectometry measurements have revealed that the film density is the same as that of the bulk one.

6

Superconductivity in U-T Alloys (T = Mo, Pt, Nb, Zr) Stabilized in the Cubic γ-U Structure

61%

Sowa S., Kim-Ngan N., Krupska M., Paukov M., Tkach I., Havela L.

Acta Physica Polonica A

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2016

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vol. 130

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issue 2

521-526

EN

Using ultrafast cooling (with the cooling rate up to 10⁶ K/s) helps to minimize the T-alloying concentration (T = Mo, Pt, Pd, Nb, Zr) necessary to retain the γ-U phase down to low temperatures. All investigated splat-cooled U-T alloys become superconducting with T_{c} in the range of 0.61-2.11 K. The bulk character of superconductivity can be concluded for some of the splats when comparing the specific-heat anomaly at T_{c} with the BCS theory prediction.

7

Amorphous 5f Ferromagnetic Hydrides UH_{3}Mo_{x}

61%

Tkach I., Kim-Ngan N., Maškova S., Andreev A., Matěj Z., Havela L.

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vol. 126

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issue 1

292-293

EN

γ-U metal, stabilized down to room temperature in the bcc structure by Mo doping, can absorb hydrogen at high H_{2} pressures only. The product is amorphous hydride UH_{3}Mo_{x} analogous to β-UH_{3}. Such hydrides are ferromagnetic with high Curie temperatures (up to 200 K), enhanced with respect to β-UH_{3}. Magnetic moment of U also increases. Large disorder together with high anisotropy lead to a very high coercivity, reaching 4 T at low temperatures. As amorphization normally tends to suppress magnetic ordering of U compounds, such hydrides represent a new class of materials, amorphous U-based ferromagnets with relatively high Curie temperature.

8

Electronic States of UNi_2 from Photoemission Spectroscopy

61%

Zalecki R., Kołodziejczyk A., Kim-Ngan N., Adamska A., Kowalczyk A., Toliński T., Mihalik M.

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EN

We measured the angle-resolved ultraviolet and X-ray photoemission spectra of UNi_2 single crystal. The valence band angle-resolved ultraviolet photoemission spectra were compared to the accessible band structure calculations. For UNi_2 the lowest binding energy strong emission at about -0.1 eV comes from U 5f states and overlaps with the Fermi edge. A small feature at -0.6 eV was ascribed also to U 5f electrons with more localised character. The higher-energy two-peak structure at about -1.2 eV and -2.1 eV comes from Ni 3d states. X-ray photoemission spectroscopy shows the standard two-line spin-orbit splitting of the Ni 2p states and of the U 4f states. Some hybridisation of the Ni 3d and U 5f state was observed in the spectra. The pronounced satellites to the Ni 2p and 3p states, associated with the on-site Coulomb repulsion and other electron correlation energies, were observed.

Refine search results

Oxygen Emissions from Single-Crystalline Fe_3O_4 Surfaces Induced by Low-Energy Ion Bombardments

Scanning Tunneling Spectra and Low Energy Ion Scattering Studies of the Verwey Transition in MBE Fe_3O_4 (100) Thin Film

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

Surface Investigations of Selected Materials by Low-Energy Ion Scattering Technique

Interface Properties of Single and Bi-Layer Fe_3O_4 Films Grown on MgO(001) Studied by RBS and Channeling Experiments

Superconductivity in U-T Alloys (T = Mo, Pt, Nb, Zr) Stabilized in the Cubic γ-U Structure

Amorphous 5f Ferromagnetic Hydrides UH_{3}Mo_{x}

Electronic States of UNi_2 from Photoemission Spectroscopy