Accommodation (reptation) is a magnetizing process which occurs when the field is cycled between two extrema. The resulting minor loops do not close upon themselves, but rather approach a closed limit cycle with each application of the applied field extrema. This paper shows that there is significant accommodation in an evaporated nanograin iron powder. The shape of the accommodating loops depends on the applied field extrema.

Magnetic properties of three kinds of nanograin Fe powder were studied. The first two, designated as NM(Ar) and NM(N), were obtained by ball milling the iron powder under an argon or nitrogen atmosphere. The third, designated NN, was obtained by evaporation and condensation. They have grain sizes of 20, 7, and 60 nm, respectively. The particle sizes of the first two were in the micrometer range, whereas those of the NN were in the nanometer range. The NN powder exhibited a coercivity of 79 mT; its magnetic moment at saturation was lower than that of bulk iron. The coercivities of the NM(N) and NM(Ar) were much smaller and their magnetic moment values at high fields were closer to that of bulk iron (210 A⋅m2/kg). The NM(N) and NN samples exhibited marked time dependences of the magnetic moments following a relatively abrupt change of the applied field. The moment changes by more than 0.5% of the saturation moment within 50 min and continues to change for many hours. Much smaller effects were detected in the NM(Ar) sample. The viscosities were investigated as a function of temperature and jump field. The results showed differences in the behavior of the three samples. The powders were consolidated by cold isostatic pressing followed by sintering at around 600 °C for several hours. The magnetic behavior of the sintered samples approach that of bulk iron.

We report on low-field measurements of the Meissner effect in a BYCO high-T-c superconductor with large pinning, The positive Meissner effect (PME) observed at low fields in a SQUID magnetometer is shown to be an artifact arising from the presence of a small field gradient. No PME is observed using an extraction technique to measure the magnetization.

A compositionally modulated alloy of 3 nm layers each of Cu and Co was electrodeposited on a (100) oriented Cu single crystal substrate. Anisotropy with fourfold symmetry in the plane of the film was investigated using ferromagnetic resonance, vector VSM techniques, and measurements of magnetic viscosity. This anisotropy is thought to be the first such effect to be observed in multilayered samples produced by either sputtering or electrodeposition. The anisotropy energy, K1, is roughly consistent with values published for fcc cobalt.

The existence of a magnetic aftereffect (magnetic viscosity) in Ni/Cu multilayered alloys was established using a vibrating sample magnetometer at room temperature and at 86 K. It was shown that the effect is strongly dependent on the step field H2 (i.e., the value the field is reduced to after the magnetic moment has been aligned in high field) and exhibits a maximum relaxation rate for values of H2 around the reverse coercive field −Hc. Aftereffect behavior of this type has been observed in other materials, although most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation in the CMA was shown to be enhanced at 86 K over its value at room temperature. New measurements over a wider temperature range show that the enhancement in this sample reaches a maximum near 120 K, but below that temperature the relaxation does freeze out. The temperature of maximum enhancement varies from sample to sample.

5 7Fe Mössbauer effect and magnetic-susceptibility measurements were performed on Y0.2Pr0.8Ba2(Cu0.98Fe0.02)3O7−δ and Y0.8Pr0.2Ba2(Cu0.98Fe0.02)3O7−δ, where δ≊0. The insulating 80% Pr compound showed susceptibility anomalies and a large hyperfine field distribution at low temperatures in addition to a hyperfine field spectrum for Fe on the Cu(2) sites. The superconducting 20% Pr compound displayed none of these effects at any temperature. After examining the alternatives, it is postulated that magnetic ordering of the Pr ions and an enhanced rare-earth transition-metal interaction due to f-electron admixture is responsible for these observations.

Magnetic measurements on Ni-Cu compositionally modulated multilayers prepared by electrodeposition indicate less diffusion of Cu into the Ni than previously obtained by either electrodeposition or other means. These samples exhibit magnetic behavior much more closely resembling that of bulk Ni than has been seen previously for Ni-Cu multilayers. No dead layer is found.

The superconducting properties of the bulk oxides La1.85Sr0.15CuO4−x and Ba2YCu3O7−y were investigated through their magnetic behavior by vibrating-sample magnetometry and complex ac susceptibility, and by dc resistivity and microwave response. These oxides were then used as targets in the preparation of thin films using a laser-ablation technique. The superconducting properties of the films were established through their microwave response. The M-H loops at low temperatures clearly establish the type-II behavior of the Ba-Y-Cu-O materials. The real part of the ac susceptibility showed the superconducting transition. Simultaneously, the imaginary part of the ac susceptibility showed the existence of nonsuperconducting portions in the samples which have a low enough resistivity to carry a significant amount of current. The novel method of microwave response was used to detect the superconductivity for both the bulk oxides and the thin films.

The purpose of this paper is to investigate the crack growth and fatigue life estimation of the optimized rivet joints in aluminum 2024 sheets numerically and experimentally. For this point, the optimal model is obtained using the Taguchi and finite element method (FEM), with respect to the cost functions and the defined levels for the parameters. The relevant geometrical parameters such as rivets length, holes diameter, and dimensional tolerances as well as pattern of where the rivets are and the material of the rivet joints are optimally determined and subsequently the fatigue life of the aluminum joint is obtained by experimental tests. The Taguchi method with its own algorithm reduced the number of experiments to 32 design points. These experiments are simulated by the FEM with a three-dimensional (3D) elastoplastic model. After the determination of optimal joint, a 3D boundary element model (BEM) of fatigue crack growth is performed on the optimal model and its fatigue life is evaluated. Then, to validate the numerical results of the fatigue life of this optimized joint, the samples are fabricated and subjected to constant-range alternative loading by a servo-hydraulic machine. The results showed that the mode of failure in the samples is the fracture at the front plate, where the punch was applied to the rivets shank and occurred in the first row. Also, the results of experimental tests for fatigue crack growth are compared with the numerical method that results in acceptable achievements.

Magnetic hysteresis loops, ac susceptibility, and resistivity measurements have been made on a Ba2 YCu3 O7−x-type high- Tc superconductor. The shape of the hysteresis loops well below Tc are reminiscent of constricted hysteresis loops observed in certain ferromagnetic materials which are usually associated with magnetic aftereffects. Similar dynamic effects, with a time constant on the order of 10 s at 40 K, are shown to be present in the superconducting material. This dynamic magnetic viscosity effect is in addition to the flux creep observed for longer time periods.

The magnetic properties of Ni/Cu compositionally-modulated alloys with [100], [110] and [111] textures were measured by magnetometry and ferromagnetic resonance. These alloys were found to exhibit a pronounced magnetic aftereffect.

The magnetic properties of iron-oxide particulates dispersed in silver (prepared by rf diode sputtering silver and iron oxide over a wide composition range) have been investigated using the Mössbauer effect, electron microscopy, and vibrating sample magnetometry. The sputtered films are nanocrystalline mixtures of immiscible particles of the two constituents (even when only a very small amount of silver is present). At room temperature, the Mössbauer effect data show that for most compositions (even those with low silver content) the majority of the film is superparamagnetic, with the fraction of material in the superparamagnetic state increasing with increasing Ag content. Consistent with these results, very narrow hysteresis loops were observed. On decreasing the temperature to near 100 K, the fraction of material in the superparamagnetic state decreased and the magnetically ordered component increased. Electron diffraction patterns clearly showed the presence of polycrystalline Ag and Fe3 O4 in the films, but composition analysis (0.03 μm resolution) was unable to separate these regions.

In the previous paper1, the concept of Mössbauer imaging was proposed. Here we report the first experimental demonstration of this concept. For simplicity, a one-dimensional imaging experiment is described; however, the fundamental imaging principle thus demonstrated generalizes, in a straightforward way, to higher dimensions. Finally, we speculate on some possible applications of this technique in materials science.