Magneto-impedance effect in soft magnetic tubes

Soft magnetic crystalline alloys have been fabricated in a tube form by ele ctrodepositing magnetic FeNi and FeNi-Al2O3 onto W fibers with a diameter o f 25 mu m. Fine Al2O3 particles have also been incorporated into the magnet ic matrix to improve mechanical properties. As-prepared materials are not m agnetically soft. With heat treatment, the magnetic properties of these com posites are similar to commercial bulk soft FeNi alloys. A giant magnetoimp edance value as large as 190% has been found in as-prepared FeNi-W with a m agnetic layer thickness of 20 mu m. This value is comparable to GMI observe d in amorphous magnetic wires. Experiments also show that GMI values decrea se when the Al2O3 content increases in a range from 0 to 7.0 at. %. This be havior is due to the increase in electrical resistivity and magnetic permea bility of the samples that modifies the skin effect. (C) 2000 American Inst itute of Physics. [S0021-8979(00)56508-6].