[en] An interstitial Pr₃(Fe,Ti)₂₉ hydride was synthesised by gas-phase hydrogenation on Pr₃(Fe,Ti)₂₉ powder using H₂. The reaction kinetics between Pr₃(Fe,Ti)₂₉ and H₂ gases was studied in a constant-volume reactor. The sample starts to rapidly absorb hydrogen, interstitially, at about 533 K. Absorption passes through a maximum at about 598 K (1.6 H/f.u) and then interstitial hydrogen desorption takes place up to the temperature of 673 K. By cooling to room temperature, the sample absorbs more hydrogen, interstitially, reaching the value of 3.6 H/f.u. By remaining at room temperature, the sample absorbs even more hydrogen reaching the value of 5.2 H/f.u. The lattice expansion observed is 2.1% and the Curie temperature, T_C, increased from 392 to 518 K. The hydride exhibits saturation magnetisation, M_S, of 145.4 and 157.5 Am²/kg at room temperature (RT) and at 5 K, respectively, anisotropy field, H_A, of 2.1 T (RT) and 4.5 T (5 K) and average hyperfine field, H_eff, of 23.3 T (RT). The magnetic anisotropy of Pr₃(Fe,Ti)₂₉ hydride is the same as that of the parent compounds, easy-cone-like, changing only in the cone angle (from 34 deg. to 26 deg.)

[en] The ternary hydride phases, DyFe₃H/sub x/ with x = 1.7, 2.5, and 4.2 all retain the PuNi₃ rhombohedral structure of DyFe₃ with a maximum volume expansion of 18% for DyFe₃H/sub 4.2/. All phases show a preferential expansion parallel to the c₀ axis. From bulk magnetization measurements, the Dy-Fe spin compensation temperature is found to decrease linearly from 545⁰K for DyFe₃ to 150⁰K for DyFe₃H/sub 4.2/ with increasing volume of the hydride phases. The ¹⁶¹Dy Moessbauer results for the two Dy sites in the structure indicate a slight reduction occurs in free-ion moment found for DyFe₃ in all hydride phases. In addition, the ⁵⁷Fe Moessbauer data show that the average Fe moment for the five inequivalent Fe sites increases with hydrogen concentration up to x = 2.5

[en] The angular dependence of coercivity in a Sm(Co_0.75F_0.12Cu_0.10Zr_0.03)_7.6 alloy is studied as a function of temperature in order to probe possible indications of a change in the reversal mechanism. The results show a gradual change of the magnetization reversal mechanism from pinning (at room temperature) to nucleation (at 500 deg. C) with a mixture of both mechanisms co-existing in a large temperature range. The relatively weak angular dependence does not agree quantitatively with the degree of grain misalignment calculated by refinement of X-ray diffraction data. Possible explanations are discussed

[en] The texture and microstrain in CoPt/Ag nanocomposite films is monitored as a function of film thickness. Perpendicular anisotropy due to (0 0 1) texturing is achieved by annealing films with thickness below 15 nm at 600 deg. C. As a function of film thickness δ the texture evolves from weak (0 0 1) below 9 nm to strong (0 0 1) at δ=12 nm which deteriorates rapidly above 15 nm and evolves to (1 1 1) above 40 nm. The strain is minimized in the range of film thickness where the (0 0 1) texturing is optimum indicating a texturing mechanism related to the reduction of mechanical strain energy

[en] Published in summary form only

[en] A program, written for the calculation of Moessbauer spectra of ⁵⁷Fe in the presence of relaxation effects in magnetically ordered polycrystalline materials has been extended to treat the case of an applied external magnetic field parallel or perpendicular to the gamma rays. The program uses the Liouville operator formalism with the usual nuclear spin Hamiltonian and an electronic spin Hamiltonian including axial and rhombic distortions in the general case of non coincident crystal field and e.f.g. principal axis systems. Model calculations with typical values of the spin Hamiltonian parameters for S=3/2 were obtained within reasonable computer times. The calculation has been applied to two cases of Fe³⁺ S=3/2 paramagnets. It was shown that satisfactory fits to the experimental spectra could be obtained only with the introduction of relaxation effects

[en] We report on the role of Ag underlayers in promoting (0 0 1) texture and perpendicular anisotropy in post-annealed CoPt:Ag bilayers and CoPt:Ag nanocomposites grown on Si(0 0 1). Films without Ag underlayers have a (1 1 1) texture. Thin (t_Ag=1.2 nm) underlayers are found to promote a strong (0 0 1) texture for CoPt thickness (t_CoPt) up to 50 nm which gradually evolves to (1 1 1) above 100 nm.The results are compared to similar studies in CoPt:Ag nanocomposites. The angular dependence of the coercivity follows a Stoner-Wolfarth rather than a pinnig type of reversal

[en] We report on a broadband technique for making frequency-swept permeability measurements of magnetic thin films. The device is essentially a strip line short circuited to the ground plane. The measurement of the input impedance of the cell loaded with the sample is modeled appropriately with an equivalent electrical circuit and the complex permeability is deduced. The technique is applied in deducing the complex permeability of thin permalloy films deposited on Si(1 0 0) substrates in the frequency range from 200 MHz to 4 GHz

[en] Members of the R₂Fe₃Si₅ series become either superconducting or magnetically ordered depending on whether the metal atom R (= rare earth, Y or Sc) is diamagnetic or paramagnetic respectively. Moessbauer effect and magnetization measurements were made to determine the magnetic state of the iron and the nature of the superconducting electrons. ⁵⁷Fe Moessbauer measurements on the Sc, Dy and Er compounds all showed two partially resolved, quadrupole split spectra at all temperatures from 300 to 1.5⁰K, indicating that there is no resolvable magnetic interaction at the iron site. No major change in the spectrum of Dy₂Fe₃Si₅ was observed in passing through its antiferromagnetic ordering temperature of approx. 4⁰K. Measurements in an applied field of 5.6 T set an upper limit of 0.03 μ/sub B/ for the iron moment in Sc₂Fe₃Si₅. However, measurements at 4.2⁰K in fields up to 7 T for the Dy compound gave an internal field approx. 9% smaller than the applied field and linear with applied field. This corresponds to an induced moment at the iron site of approx. 0.07 μ/sub B/ at 7 T applied field. The ¹⁶¹Dy Moessbauer resonance clearly showed the onset of magnetic order around 4⁰K and the magnetic moment on Dy at 1.5⁰K was found to be 7.0 +- 0.2 μ/sub B/ consistent with the magnetization measurements. The nature of the superconducting electrons in the R₂Fe₃Si₅ series is discussed in the light of available measurements

[en] It has recently been shown that many intermetallic compounds of d- and f- shell elements reversibly absorb large amounts of hydrogen to form ternary hydrides at easily accessible temperatures (0-100⁰ C) and hydrogen pressures (.01-10,000 torr). Such ternary hydrides have been considered in many energy conversion or storage applications. Two fundamental questions may be addressed regarding this class of hydrides. The first one is related to the ease with which hydrogen is absorbed from the gas phase by these intermetallics, and the second to the location of hydrogen atoms once it is absorbed in the intermetallic lattice. Hyperfine interaction measurements on a large number of systems have been carried out in relation to these questions. In many cases, measurements of this type are shown to contribute rather direct and at times unique information concerning these two aspects of hydrogen absorption. In particular, we demonstrate that conversion electron Moessbauer spectroscopy has the potential of providing evidence for the chemical and magnetic state of the surface layers in the intermetallic. This information, in turn, has direct bearing on the hydrogen absorption mechanism. Furthermore, since hyperfine interaction measurements are microscopic probes, they offer the possibility of distinguishing different local hydrogen environments surrounding a given metal atom. Information of this type can be used in conjunction with results from bulk measurements to determine hydrogen location in the metal lattice. Examples illustrating both aspects of ternary hydride formation will be discussed. (orig.)