Volume 89, Issue 3, 01 February 2001
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
89(2001); http://dx.doi.org/10.1063/1.1339855View Description Hide Description
Nanocrystalline and a composite system constituted by nanocrystalline Fe and have been synthesized by ball-milling commercial magnetite and an equimolar mixture of iron and magnetite powders. The physical parameters governing the milling process have been strictly controlled so as to achieve the nanocrystalline state of the precursor material and to avoid chemical reactions. X-ray diffraction and Mössbauer spectroscopy measurements have been carried out both on as-milled powders and on samples previously subjected to annealing treatments in the 100–600 °C temperature range. The results, providing information on the structural and compositional features of the produced samples, are discussed in terms of structural disorder which is healed by subsequent annealing. In the case of the composite system, this analysis indicates that a high mixing degree between the constituent phases has been reached. In particular, the presence of a sextet with anomalous hyperfine parameters in the Mössbauer spectrum of as-milled has been associated with an alteration of the magnetite structure at the interface with bcc Fe. For both sets of samples, the influence of the structural features on the macroscopic magnetic behavior has been investigated by performing magnetic hysteresis loop measurements at room temperature.
89(2001); http://dx.doi.org/10.1063/1.1338514View Description Hide Description
The giant magnetoimpedance (GMI) effect has been studied in layered FeSiB/Cu/FeSiB films in the frequency range of 100 kHz–40 MHz. The field dependence of the GMI ratio shows that the GMI ratio increases with magnetic field reaching a positive maximum value at a certain field, and then gradually decreases to negative values. For the layered films with a Cufilm width of 0.6 mm, the positive maximum GMI ratio is about 2%, which is smaller than the value of the negative GMI ratio (−6.6% at at a frequency of 5.2 MHz. With an increase of the Cufilm width, a positive maximum GMI ratio of 4.5% and 13.5% is obtained for and 5.2 MHz in the layered films with a Cufilm widths of 1 and 1.3 mm respectively. In addition, all the layered films exhibit a large negative GMI ratio at a relatively large field and it is associated with the easy axis orientation of the layered films. The increase of the positive maximum GMI ratio with an increase of Cufilm width at 5.2 MHz may be due not only to the effect by the increase of Cufilm width, but also to the difference in the easy axis orientations of the layered FeSiB/Cu/FeSiB films.