Mössbauer study on the magnetic state of iron particles in Fe-N and Fe-Zr-N soft magnetic thin films

The magnetic state of -Fe particles and the behaviour of nitrogen and zirconium during annealing in Fe₉₆N₄ and Fe_85.6Zr_7.6N_6.8 magnetic thin films have been studied by conversion electron Mössbauer spectroscopy for ⁵⁷Fe. The crystalline phases present in the Fe-N annealed films were -Fe and -Fe₄N, and those in the Fe-Zr-N annealed films were -Fe and ZrN. In the Fe-N films annealed below 300°C, about 60% nitrogen is incorporated interstitially into -Fe and the rest is used for the formation of -Fe₄N. In the Fe-N film annealed at 500°C, almost all nitrogen participates in the formation of -Fe₄N, leading to the grain growth of -Fe particles and an increase in coercive force. The values (291–325 kOe) of internal magnetic field of iron sites in -Fe in the Fe-Zr-N films are much smaller than that (333 kOe) of the iron site in pure -Fe. Even if the Fe-Zr-N films were annealed at 500–700°C, some zirconium and nitrogen is still incorporated substitutionally and interstitially into -Fe, respectively. In particular, the substitutional zirconium depresses the grain growth of -Fe particles, perhaps due to a chemical interaction between zirconium and iron.     

Functionalized surfaces of polylactide modified by Langmuir–Blodgett films of amphiphilic block copolymers

To modify the surface of poly(L-lactide) (PLA) supports, we have investigated the feasibility to deposit on the PLA surface Langmuir–Blodgett films of amphiphilic block copolymers based on poly(L-lactide). AB and ABA block copolymers were prepared with PLA as the A block and either poly(ethylene oxide), -methoxy--hydroxy poly(ethylene oxide), -carboxy--hydroxy poly(ethylene oxide) or poly(L-aspartic acid) as the B blocks. Films with phase-separated hydrophilic and hydrophobic blocks in a bilayer brush structure were prepared by compression of the copolymer Langmuir films on the water/air interface. The interfacial behavior of the monolayers and the effect of the copolymer composition on the phase separation was followed by measurements of the surface-pressure/area isotherms using a Langmuir trough and by contact angle measurement of deposited Langmuir–Blodgett (LB) films. The phase separation of the hydrophilic and PLA blocks is more effective in diblock AB copolymers compared with triblock ABA copolymers. The presence of ionic groups in the hydrophilic chains facilitates penetration of hydrophilic segments into the water subphase. Dynamic contact angle measurements were used to study the stability of the LB-films transferred on the PLA support and the changes in the surface properties upon incubation of surfaces in water.     

Synthesis, crystal structure and X-ray powder diffraction data of the phosphor matrix 4SrO·7Al2O3

The white phosphor matrix 4SrO·7Al₂O₃ has been synthesized by firing the appropriate mixture of SrCO₃, Al(OH)₃ and H₃BO₃ in the molar ratios 1:3.5:0.135 at 1300°C for 4–7 h. The crystal structure of 4SrO·7Al₂O₃ has been determined as a orthorhombic Pmma space group with a=24.7451(2)Å, b=8.4735(6)Å, c=4.8808(1)Å, V=1023.41(3)ų, Z=2, and D=3.66 g cm^–3 by the Rietveld analysis. The refinement figures of merit are R_p=8.26, R_wp=11.60, R_bragg=4.44 and s=2.61 for 844 reflections with 2<119.94°. And the corresponding X-ray powder diffraction data are presented for search/match analysis.     

Pressureless sintering of β-SiC with Al2O3 additions

-SiC was pressureless sintered to 98% theoretical density using Al₂O₃ as a liquid-phase forming additive. The reaction between SiC and Al₂O₃ which results in gaseous products, was inhibited by using a pressurized CO gas or, alternatively, a sealed crucible. The densification behaviour and microstructural development of this material are described. The microstructure consists of fine elongated -SiC grains (maximum length 10 m and width 2–3 m) in a matrix of fine equi-axed grains (2–3 m) and plate-like grains (2–5m). The densification behaviour, composition and phases in the sintered product were studied as a function of the sintering parameters and the initial composition. Typically, 50% of the -phase was transformed to the -phase.     

The martensitic transformation in cold-worked Fe-Mn alloys studied by Mössbauer spectroscopy

The effect of cold-working on 16, 23 and 30 at% Mn iron-manganese alloys (C<0.05 at%) has been examined using Mössbauer spectroscopy and X-ray diffractometry. The induced martensitic transformation , depends on the composition and on the initial structure. It is found that the transformation in presence of the phase occurs only at high deformations.     

The structure of the γ′ extended solid solution in a splat-cooled Ag-50 at.% Cu alloy

The structure of the extended solid solution in electron transparent areas of a splatcooled Ag-50 at.% Cu alloys was examined by transmission electron microscopy. This phase was usually found to be spinodally decomposed at large grain sizes (–1m in diameter), in contrast to X-ray diffraction data indicating that the solid solution was undecomposed. A solidification model for rapidly quenched eutectic alloys is proposed to account for the observed structure of the splat-cooled alloy. A transformation curve for the spinodal decomposition of is also calculated and related to predictions derived from the solidification model.     

Heat conduction in a multilayer composite wedge

A new method for analytically solving a problem of steady-state heat conduction for multilayer composite wedge-shaped bodies is suggested based on a generalization of the integral Mellin transform.Notation T temperature - _rr, thermal conductivity coefficients - thickness of composite material layers (1) - N₁(), N ₂ ⁽¹⁾ (), N ₂ ⁽²⁾ () auxiliary local functions from the rapid variable =r/ - m(r, p) auxiliary function entering the core of the generalized integral Mellin transform - ₀ half of the wedge aperture angle Moscow Institute of Chemical Engineering. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 4, pp. 487–491, April, 1993.     

Microhardness response of nitrogen-implanted and X-irradiated lithium fluoride

The microhardness behaviour of {001} faces of LiF has been investigated before and after both nitrogen-ion implantation and implantation followed by X-irradiation. Implantation alone produced no changes in either hardness or dislocation etch-pit rosette sizes on the surface, though radial indentation fracture was promoted. Implantation followed by X-irradiation produced high densities of colour centres deep into the crystal, much deeper than the implantation damage depth (0.2m). Hardness and rosette sizes were affected to depths of 150m, which was less than the colouration depth. Thus the colour centres producing the colour are probably different from those impeding dislocation motion.     

Third sound in3He-4He mixture films

We report third-sound studies of³He-⁴He mixture films for 0.3T1.8 K carried out in two different experimental situations. In one experiment detailed measurements of the amplitude of both the temperature and thickness variation of the film were made for pure⁴He and the results for |T/d| are in good agreement with the predictions of Bergman. Mixture studies in this apparatus were made difficult due to the presence of capillary condensation. In spite of this a number of interesting results are reported. Subsequent measurements were made in a new apparatus where capillary condensation effects could be demonstrably avoided. Helium films of 5.7 layers of⁴He were studied as a function of added amounts of³He. BelowT0.7 K the third-sound measurements are consistent with model calculations based on a bilayer film. We conclude that for 0.3T0.6 K films of the type we have studied are isotopically layered in the van der Waals field provided by the substrate.     

Dielectric properties of thin solid films formed on silicon

We report on the measurement of the frequency-dependent complex permittivity, ()=()-i(), over the frequency range, 30 MHz to 6 GHz, of silicon wafers and of thin dielectric films formed on silicon. Measurements, as a function of temperature and time treatments, were obtained by means of an HP Network Analyzer and dielectric probe and the resulting ()and()plots for the silicon wafers are shown to have a Debye-type [1] profile, thereby indicating that the associated polarization mechanism is of the orientational variety.     

An Interpretation of Dispersionless Modes in Neutron Diffraction Experiments on Helium Films

We analyze the dynamic structure function S(q, ) for neutron scattering off helium films in the direction perpendicular to the substrate. Dispersionlessmodes that have been found in neutron diffraction experiments on helium films adsorbed on graphite powder (H. J. Lauter, H. Godfrin, and H. Wiechert, Excitations in ⁴ He films, in Proceedings of the Second International Conference on Phonon Physics, World Scientific, 1985) are interpreted as standing waves or resonances of the helium liquid perpendicular to the substrate. Our interpretation is supported by microscopic calculations of the ⁴He dynamic structure function.     

Suppression of Anomalous Allotropic Transformations at High Pressures

Anomalous allotropic transformations accompanied by a reduction in the density of the substance can be suppressed by applying a high pressure equal to the ratio of the heat of transition to the difference in the volumes of the phases involved. The estimated pressures necessary to suppress the (ZrO₂), (Fe), and (Sn) phase transitions are 4.34, 3.00, and 0.495 GPa, respectively.     

Plasma spraying of ferrites

The production of thick films (> 20 m) of polycrystalline ferrite by the arc plasma deposition process is described. Operating conditions of a plasma torch of the authors' own design are quoted. As-sprayed films have high electrical conductivity and low magnetic permeability, but these parameters are restored close to the bulk values by annealing. The surface finish of the films is coarse and unaffected by the particle size of the powder sprayed.     

Effect of resonant impurity scattering on collective mode peaks in the ultrasound attenuation of heavy fermion superconductors

We have calculated the attenuation of longitudinal ultrasound due to real order parameter fluctuations in impure polar and planarp-wave superconductors. The quasiparticle self-energy and the corresponding vertex corrections have been included in thet-matrix approximation for arbitrary scattering rate =1/2_N and all scattering phase shifts _N (0 _N/2). We obtain sound attenuation peaks belowT _c whose heights, positions, and shapes depend on ₀ (sound frequency), (₀), _N, and (coupling strength due to particle-hole asymmetry). The peaks become much more distinct and sharper for _N =/2 (resonant scattering by impurities) than for _N=0 (Born approximation). By choosing , _N, and suitably, qualitative agreement between calculated and observed peaks in UBe₁₃ and UPt₃ can be achieved.     

Knudsen molecular flow in a channel with a small temperature difference at its ends

The thermomolecular pressure difference (TPD) of helium, argon, and krypton is measured in a packet of glass capillaries for temperatures 273 and 293 K at their ends in a 10–100 range of Knudsen numbers.Notation exponent of the thermomolecular pressure difference effect - Kn Knudsen number - rarefaction parameter - Q_T reduced thermal creep flux - Q_P reduced Poiseuille flux - C(_t) Cercignani-Lampis scattering kernel - R specular scattering kernel - (1 – ) fraction of specular reflection - _t accommodation coefficient of the tangential momentum - P_c, P_h gas pressure in the cold and hot volumes, respectively - coefficient of dynamic viscosity - m mass of gas molecules - k Boltzmann constant - D, L the capillary diameter and length, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 719–724, May, 1988.     

Measurement of the Thermal Diffusivity of Metallic Foils and Films by the Photoacoustic Method1

The thermal diffusivities of four kinds of metallic foils from 20 to 200m in thickness were measured by a photoacoustic method on the basis of the Rosencwaig and Gersho theory. The measured data for continuous foils of uniform microscopic structure almost agreed with the literature values. Measurements were also carried out on two kinds of metallic thin films with of 10m thickness produced by sputtering. The difference in thermal diffusivity between the foils and the sputtered films depended on the uniformity of the microscopic structure.     

Amplifier based on a field-effect triode with negative current feedback

Conclusions A field-effect triode amplifier with series negative current feedback allows a voltage gain of the order of 200–300 to be obtained for a load resistance R_s1 M. The coefficient K_u begins to decrease noticeably only for a feedback resistance above 500 .The current gain reaches (8–10)·10³. Increasing the resistances R_s and R_L to hundreds of ohms has practically no effect on K_i. For a further increase of R_s and R_L the coefficient K_i decreases.The power gain reaches its maximum value (of the order of 10⁴ or more) for R_s100 and R_L=10–100 k. An increase in R_s leads to a reduction of K_pmax and to a shift of the extremum of the function K_p=f(R_L) into the range of higher values of R_L.A large input resistance of the amplifier (tens of megohms and higher) is obtained when R_s increases to 10–100 M. The maximum input resistance is obtained for R_L and R_s and may exceed values of from hundreds of megohms to several gigaohms. The minimum input resistance is hundreds of kilohms for R_L and R_s0.The minimum input resistance (5–10 k or less) is ensured for R_g and R_L0. An increase of the output resistance to hundreds of megohms or higher occurs for R_g and R_s.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 67–70, September, 1971.     

Instantaneous plastic strain associated with stress changes during the steady state creep of Al and Al-4.20 at% Mg alloy

The instantaneous strains resulting from stress changes during steady state creep of polycrystalline aluminium and an Al-4.2 at % Mg alloy in the temperature range 100 to 300° C, have been determined. Instantaneous plastic strains were found in both materials for stress increments and decrements. For polycrystalline aluminium the instantaneous plastic strain on a stress increment, (+), was considerably larger than the instananeous strain on a stress increment, (–), whereas for Al-4.2 at % Mg (+) was approximately equal to (–). Work hardening rates determined from (+) and (–) for polycrystalline aluminium vary from about one-tenth to one-half of Young's modulus and depend strongly on temperature and stress. The need to improve existing creep theories to include both climb (recovery) and glide components is suggested.On leave from Department of Engineering Materials, University of Windsor, Windsor, Ontario N9B 3P4, Canada.     

Superconducting state in M3C60: Strong vs. weak coupling

The superconducting state in the doped fullerenes is due to strong coupling (e.g.,2.1 for Rb₃C₆₀) to low-frequency intramolecular modes _L 250 cm^–1 (^21/2). The analysis is based on an equation describingT _c for any strength of the coupling and on recent isotope effect and NMR data.     

Anisotropic magnetic properties of obliquely deposited Ni films

Magnetic properties of evaporated nickel films, deposited onto 75 m thick 300 H Kapton substrates by evaporation at oblique off-normal angles of incidence, were investigated by SQUID magnetometry. We found that, in the film plane, the direction of easy magnetization lay perpendicular to the incidence plane for films deposited at < 50°. At large s, the easy axis changed to the direction parallel to the incidence plane. The anisotropy, coercivity and squareness of the hysteresis loops increased with an increase in . The results may be qualitatively understood from the presence of an inclined columnar structure with shape anisotropy governing the demagnetization of the magnetic fields.