Band 100, Heft 9

It has been claimed by R. Sietmann that the attribution of the discovery of the so-called ‘Auger’ effect to Pierre Auger was a false attribution and that Lise Meitner should have got the credit for that discovery. However Sietmann himself recognised that Meitner's description of this effect was ‘buried in’ two larger papers whose primary concern was nuclear physics. Sietmann only mentioned Auger's 1925 article and did not mention his 1923 article, an omission now found in many places. We examine again L. Meitner's and P. Auger's contributions to the description of the ‘Auger’ effect. Meitner's concern was the exact nature of the (nuclear) beta radiations about which she opposed Ch. D. Ellis, and this had been the subject of an intense Berlin–Cambridge controversy where Ellis' description eventually prevailed. Auger's observations were the central theme of his PhD thesis at the J. Perrin's laboratory on the composed photoelectric effect. We thus believe that while L. Meitner should have shared the Nobel Prize with O. Hahn, the Auger effect has rightly been attributed to Auger.

Applied surface and interface analysis methods such as Auger electron spectroscopy and X-ray photoelectron spectroscopy are particularly well suited to studying intergranular segregation. In the case of internal interfaces such as grain boundaries, they must be transformed into two open surfaces by intergranular fracture. The main task is quantification of the measured spectra. Advantages and disadvantages of different approaches are discussed. It is shown that only for very low segregation levels do the simple and modified ratio methods give acceptable results. With increasing amount of enrichment, the more complicated methods with full description of the contribution of the first few monolayers to the total measured intensity have to be applied in order to obtain reliable concentration values that are useful for the determination of the concentration- and temperature-independent standard enthalpy and entropy of segregation.

Mechanical loss measurements were performed at high temperature in fine-grained ceramics, such as zirconia and alumina. At high temperature, the mechanical loss increases exponentially with temperature, which accounts for material creep. The results are analyzed with a model of grain-boundary sliding lubricated by an intergranular glassy phase. When the amount of the intergranular glassy phase is higher, the mechanical loss level is globally higher and so is the creep rate. On the other hand, doping fine-grained ceramics with nano-sized reinforcements such as multiwall carbon nanotubes results in a decrease in the high-temperature mechanical loss. In this case grain-boundary sliding is more difficult and as a consequence better creep resistance is observed.

The fatigue-induced modifications of the structure of power devices on components that underwent extreme electro-thermal fatigue were investigated, with special attention to the behaviour of the Al metallization layer. Electrical cycling induced a moderate grain growth in the metallization layer, except for the regions located beneath the connection wires. There the wire bonding process is associated with severe plastic deformation, leading to a fragmentation of the initial grains and significant grain growth. Grain-boundary grooving is another example of fatigue-induced structural changes: it reveals an intense stress- and temperature-driven grain boundary diffusion process.

Systematic magnetic and specific-heat studies of hydrides of ternary compounds on the basis of rare earths or actinides help to unravel different roles of f-states in these two classes of materials. In rare earths, H absorption tends to suppress magnetism by weakening the exchange interaction mediated by conduction electrons. Light actinides exhibit a 5f band of variable width at the Fermi level and the hydrogenation makes magnetic features typically stronger. 5f band narrowing due to volume expansion is responsible for this net tendency, but the effects of H bonding cannot be neglected.

We performed magnetic measurements on the hydrogenated system (U, Th)CoSn as part of an investigation of UTX compounds (T – transitional metal, X – p-metal). The U 1– x Th x CoSn compounds crystallize in the hexagonal structure (ZrNiAl type, space group P 2m). Hydrogen absorption of approximately 1 H/f. u. could be achieved. The hydrogenation does not change the crystal structure. In all cases it leads to a unit-cell expansion by 3.0 % to 3.6 %. Studies of the temperature dependence of the magnetic susceptibility indicate a certain increase in the Curie temperature T C in the hydrides, but the Th concentration at which ferromagnetism vanishes remains practically unchanged (U 0.2 Th 0.8 CoSn has a paramagnetic ground state).

We present the results of specific heat, magnetization and susceptibility measurements performed on single crystals of PrPdSn and NdPdSn intermetallic compounds. Both compounds crystallize in the orthorhombic TiNiSi-type crystal structure and order antiferromagnetically at T N = 4.2(1) K (PrPdSn) and T N = 3.5(1) K (NdPdSn). NdPdSn also undergoes an order-to-order phase transition at T 1 = 1.95(3) K. Both compounds exhibit high magnetocrystalline anisotropy at low temperatures and a complicated magnetic structure, which is underlined by the metamagnetic phase transitions of both compounds.

Finite-temperature magnetism of Ni-based transition metal alloys with the face-centered cubic structure is studied theoretically in the framework of the first-principles approach. Calculated total and local magnetic moments agree well with experiment. The mean-field approximation, the random-phase approximation (RPA), as well as the renormalized RPA extended to random alloys are used to estimate the Curie temperature. The most satisfactory agreement with the experiment for a broad class of Ni-based alloys Ni (M = Cu, Fe, and Mn) over the whole concentration range isobtained by using the renormalized RPA approach.

Superlattices of 15 periods of (GaSb/Mn) with bilayer periods of 3 nm and 10 nm were grown on a GaAs(001) substrate by laser ablation and studied by X-ray glancing-incidence reflectometry. Both qualitative analysis and quantitative treatment of the X-ray reflection curves allow us to restore the depth profiles of the core electron density into the samples studied and to estimate the diffusion depth of Mn atoms into adjacent thicker GaSb layers, which appeared to be 3.5 nm thick.

Due to hydrogenation, the crystal structure of GdNiAl distorts from hexagonal to orthorhombic. The magnetic ordering temperature decreases dramatically and the magnetic entropy of this phase transition is in good agreement with theory. LuNiAl does not change its structure type, but it was found that the electronic contribution to specific heat decreases dramatically. None of the two phases loses its metallic character.

Antiferromagnetic order at T N = 21 K was discovered in the intermetallic compound HoZn 5 Al 3 , which crystallizes in its own structure type. A metamagnetic transition can be induced by magnetic fields of 4 T. Enormous values of specific heat below 1 K are attributed to the Ho nuclear specific heat.

We present a study of the magnetocaloric effect in selected substituted RCo 2 compounds. The first system was Gd(Rh x Co 1 – x ) 2 with x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30. The substitution of Co by Rh leads to a decrease in the critical temperature with increasing rhodium content from T c = 350 K for x = 0.05 to T c = 200 K for x = 0.30. The maximum entropy change slowly increases with increasing Rh concentration and reaches about 1 J K – 1 kg – 1 for x = 0.30 and a field change of 1 T. The second studied system was Dy(Fe x Co 1 – x ) 2 with x = 0.00, 0.01, and 0.03. The critical temperature as well as the magnetic entropy change strongly depends on the Fe concentration. The transition temperature increases from 140 K in DyCo 2 to 210 K for 3 % Fe but the maximum of the entropy change quickly decreases from 5 to 1.2 J K –1 kg – 1 for field of 1 T.

Thickness modes of magnetoelastic waves in a bi-layered structure magnetic–non-magnetic material have been theoretically investigated. Plots illustrating the dependence of harmonics of resonant frequencies upon the magnetic layer thickness were constructed at various magnetoelastic wave vectors. A dependence of the dimensional resonance frequencies on the wave number of magnetoelastic waves propagating along the saturating field direction is found. Peculiarities of the resonant frequency harmonics behavior with varying magnetic layer thickness and number are analyzed. The multimode character of the thickness magnetoelastic resonances, attributed to the possibility of excitation of magnetoelastic waves with different wave number is discussed.

The influence of equal channel angular pressing (ECAP) on the microstructure changes of magnesium alloy AZ31 was investigated. The microstructure changes were correlated with electrochemical characteristics of the surface. Eight passes of ECAP resulted in significant grain refinement (factor 100) of the initial squeeze-cast (SC) alloy. The influence of microstructure changes on electrochemical properties of the surface was evaluated using electrochemical impedance spectroscopy. The variation of electrochemical characteristics of the surface of the SC and ECAP alloy was determined after 3 and 7-day exposure in the corrosion solution of 0.1 M NaCl. The fine-grained deformed structure after ECAP was found to have significantly higher charge transfer resistance as compared to the squeeze-cast material.

The effects of severe plastic deformation on the mechanical properties and deformation behavior of Gum Metal with a nominal composition of Ti-36Nb-2Ta-3Zr-0.3O (mass.%) were investigated using high-pressure torsion (HPT). Applying the HPT process, the alloy shows ultra-low Young's modulus, high strength, extended elastic limit, high ductility, and very low hardening during HPT. The tensile strength of Gum Metal increases with increasing equivalent strain, while work hardening is much smaller than reported values for other common metallic materials. The deformation structure is composed of ultrafine grains produced by transgranular shear through application of HPT. These results suggest that the strengthening mechanism of Gum Metal is attributable to a unique plastic deformation which operates in the region where the local stress reaches values close to that of ideal strength.

The results of high-resolution X-ray diffraction and X-ray glancing-incidence mirror reflection studies of structural characteristics of the GaAs/Ga 1– x In x As/GaAs diluted magnetic semiconductors, with an Mn δ-layer well separated from the Ga 1– x In x As quantum by the GaAs spacer, are presented. A strong correlation between the structural, magnetic, electro-physical and optical properties of the samples gives evidence that the samples consist of a distribution of ferromagnetic and paramagnetic regions. Such a phase separation can be understood by a non-random distribution of the local magnetic moments and fluctuations of the exchange interaction in the samples having semiconductor-type conductivity.

Doping the Bi2212 phase by Pb usually results in an enhancement of the pinning properties and the T c . Using elements other than Bi and/or other sites one may obtain opposite results. In this work we present the effect on structural and magnetic properties of Bi2212 superconducting ceramics when co-doping with La and Pb is used. Bi 1.4 Pb 0.6 Sr 2 Ca 1– x La x Cu 2 O 8 +δ (0 ≤ x ≤ 0.025) superconducting ceramic samples were prepared using a solid-state reaction method. Structural and magnetic characterizations were made by means of X-ray diffraction, scanning electron microscopy and AC susceptibility measurements. The obtained crystalline structure is mainly tetragonal with a c-axis lattice parameter decreasing with La content. Substitution by La reduces the fraction content of the parasitic phase Bi2201 and the size of the grains. The transition temperature T c is enhanced quasi linearly with the La content and the superconducting volume fraction has a maximum for x = 0.01.

The effect of hydrogenation on magnetic properties of the weakly ferromagnetic superconductor UCoGe was studied. UCoGe hydrides were synthesized at T = 773 K at different pressure of H 2 gas (8, 5, 2 bar). The hydrogenation at 8 bar and 5 bar results in a change of the crystal structure from orthorhombic (TiNiSi structure type) to hexagonal (ZrBeSi type) with H concentrations just below 2 H/f. u. For one of such β-hydrides, UCoGeH 1.7 , the Curie temperature increases from 3 K up to 50 K and the spontaneous magnetic moment from 0.03 μ B/f . u. to 0.05 μ B/f . u. An α-hydride of UCoGe (ΔV/V = 0.25 %) with a hydrogen concentration 0.1 H/f. u. was obtained at 2 bar. It has the same crystal structure as a pure compound and surprisingly exhibits no magnetic order.

Nanolayers were deposited onto surfaces of n-type InP single crystal wafers by electrophoresis from reverse micelle colloid solutions containing palladium nanoparticles. Two types of nanolayers were deposited, by applying a positive potential or a negative potential on the InP wafer. Further, wafers with nanolayers were annealed in high vacuum at 400 °C. The nanolayers were studied using capacitance–voltage characteristics on a mercury probe, by atomic force microscopy and by secondary-ion mass spectroscopy. Two types of Schottky-like diodes were prepared on wafers with the two types of nanolayers and studied by current–voltage characteristics. The diodes with nanolayers deposited by applying the positive potential, which contained Pd nanolayers, showed characteristics with better rectifying properties than the other type of diodes. Correlations among measured characterizations were found.

A detailed theoretical study of the structure and electric field gradients (EFG) of the Zr 2 Ni compound is presented. Using all-electron augmented plane waves plus local orbitals formalism, the equilibrium volume, bulk modulus, and EFGs at both non-equivalent crystallographic positions, Zr and Ni, are calculated. The possible mechanism of formation of the EFGs at both sites are analyzed and discussed. We have also performed supercell calculations with Cd and Ta impurities. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Cd and Ta probe atoms in the time-differential perturbed angular correlation measurements of this compound.

Solution growth of Gd–Cu–Al resulted in the formation of single crystals of GdCu 4 Al 8 with tetragonal ThMn 12 -type structure (a = 8.751 Å, c = 5.148 Å), Gd 2 Cu 9.4 – 6.7 Al 7.6 – 10.3 with hexagonal Th 2 Zn 17 -type structure (a = 8.83 Å, c = 1.28 Å), and Gd(Cu, Al) 4 with orthorhombic CeNi 2+ x Sb 2 – x -type structure. An antiferromagnetic ordering of GdCu 4 Al 8 was found below 35 K, which is in agreement with the previously reported T N = 35 K and T N = 32 K measured on polycrystalline samples. In the temperature range 50 – 320 K the magnetic susceptibility χ follows the Curie–Weiss law with μ eff = 7.8 μ B/f . u. and θ p = – 17 K for B c, μ eff = 7.9 μ B/f . u. and θ p = – 18 K for B ⊥ c. The a-axis is the easy magnetization direction. The Gd(Cu, Al) 4 and Gd(Cu, Al) 4 compounds order antiferromagnetically below T N = 35 K and T N = 31 K, respectively.

Here we present an analysis of the low-temperature specific heat of selected nitrides (Cr 3 GaN, GaN, and InN) and niobates (CaNb 2 O 6 , Ca 2 Nb 2 O 7 , and Sr 2 Nb 2 O 7 ). The low-temperature specific heat is considered as a sum of electronic and phonon contributions, where the electronic part is almost negligible. The phonon specific heat is then described using an additive combination of the Debye and Einstein approaches for acoustic and optical phonons, respectively, together with the correction for the anharmonicity of the phonon spectrum.

The electronic structures of rare-earth-filled skutterudites have been investigated by high-resolution photoemission spectroscopy. In order to reveal their bulk nature, the bulk-sensitive photoemission spectroscopy with soft X-ray (hv∼800 – 1100 eV) and hard X-ray (hv∼8000 eV) is a very powerful tool since the rare-earths' valence and electronic structures on the surface are often different from those in the bulk. Our experimental results clearly show the coexistence of the strongly mixed-valence state and the heavy-fermion state in SmOs 4 Sb 12 and the quasi-particle peak near the Fermi level in PrFe 4 P 12 induced by the hybridization between the rare-earth 4f and conduction electrons.

Frequency and temperature dependences of the impedance components have been investigated in darkness and under illumination for PbTe(In) nanocrystalline films. Synthesis of the films was performed using evaporation of a target source to a cooled glass substrate. The films have a column-like structure with a mean grain size varying from about 60 nm to 170 nm depending on the deposition temperature. Analysis of the data obtained revealed that the conductivity of the films is determined by two mechanisms: charge transport along the inversion channels at the grain surface and activation through barriers at the grain boundary. Persistent photoconductivity appears in the films below T = 150 K. The frequency dependence of the relative photoresponse has a pronounced maximum. The photoresponse in the ac mode may be higher by two orders of magnitude than in the dc measurements.

X-ray photoelectron spectroscopy (XPS), electron microprobe microanalysis (EPMA), and secondary ion mass spectrometry (SIMS) have been used for analyzing the chemical composition in surface layers of iron-base alloys. Samples analyzed in this study were a ferritic Fe–Mn alloy annealed under low partial pressure of oxygen and an austenitic Fe–Mn–Si–Cr alloy annealed under vacuum. The XPS results showed that manganese was enriched and oxidized while iron was metallic in the surface layer of the Fe–Mn alloy annealed under a low partial pressure of oxygen. The EPMA results showed that manganese was depleted while chromium was enriched in the surface layer of the Fe–Mn–Si–Cr alloy annealed under vacuum. The SIMS depth profiles coupled with the EPMA results indicated that the enrichment of chromium in the surface layer improves the oxidation resistance of the alloy. The enrichment and depletion of manganese in the surface layer is discussed on the basis of the thermodynamic properties of the iron–manganese system.