Influence of hydrogen on magnetic properties of soft magnetic amorphous alloys
The influence of electrolytic hydrogenation on the magnetic properties of three different kinds of amorphous alloys has been investigated. The alloys studied were Fe/sub 83.3/Si/sub 3.5/B/sub 11.2/C/sub 2/, Fe/sub 38/Ni/sub 38/Mo/sub 2/Si/sub 8/B/sub 14/, and (Co/sub 86/Fe/sub 5/Cr/sub 9/)/sub 75/Si/sub 10/B/sub 15/. The experimental results showed that after hydrogenation the samples became very brittle and the soft magnetic properties degraded dramatically, but saturation magnetization sigma /sub s/ and average hyperfine field increased markedly. As hydrogen evolved from the charged samples which were placed in air at room temperature, the magnetic properties, toughness, and average hyperfine field were gradually recovered. >
Hydrogen induced anisotropy in magnetic amorphous ribbons
A study about induced anisotropy by hydrogen charging has been performed in both, positive and negative magnetostrictive amorphous alloys. A strong perpendicular to surface anisotropy at the sample surface in every hydrogenated sample has been observed from Bitter pattern and from hysteresis loops obtained by magnetooptical Kerr effect. This perpendicular anisotropy is only in the volume fraction near to sample surface, as it is inferred from hysteresis loops and magnetization curves measured by induction. A model assuming that the large perpendicular induced anisotropy is due to the mechanical stresses produced by the change of volume of the hydrogenated zones has been developed. From this model, by fitting experimental results, anisotropy energy, internal stresses, and hydrogen charged volume have been calculated.
Atmospheric drag effects on the KOMPSAT-1 satellite during geomagnetic superstorms
We examine the atmospheric drag on the low earth-orbiting satellite, KOMPSAT-1 in a sun-synchronous orbit at ~685-km altitude starting in 1999, during a 3-month (October-December) period in 2003. This 3-month interval includes the October 29-30 and November 20 magnetic superstorms and weak to moderate storms. We observed that the daily KOMPSAT-1 drag acceleration transiently responses to transient storm-time disturbances. That is, there is an one-to-one correspondence between the KOMPSAT-1 drag accelerations and the storm events. We find that the drag acceleration correlates strongly with the level of geomagnetic disturbance. This indicates that the trajectory of KOMPSAT-1 is significantly perturbed during extremely disturbed intervals because of atmospheric density increase. The main contributor to the density increase is Joule heating associated with the geomagnetic activity rather than the solar EUV radiation, as reported by previous studies. We suggest that understanding how the upper atmosphere responses to the geomagnetic-associated heating is important to predict space weather impacts on low earth-orbiting satellites.