  A study of magnetic hysteresis and Giant magnetoimpedance (GMI) in amorphous
glass covered Co-Si-B and Co-Mn-Si-B wires is presented. The wires, about 10
microns in diameter, were obtained by glass-coated melt spinning technique.
Samples with positive magnetostriction (MS) have a rectangular bistable
hysteresis loop. A smooth hysteresis loop is observed for wires with nearly
zero MS. When MS is negative, almost no hysteresis is observed. The GMI was
measured in the frequency range between 20 Hz and 30 MHz. The shapes of the
impedance versus field curves are qualitatively similar to each other for both
positive and zero MS samples. Impedance is maximum at zero field, and decreases
sharply in the range 10-20 Oe. For the negative MS wires, when the driving
current is small, the impedance is maximum at a finite external field. The
position of the maximum approaches zero with increasing current. The
contributions of the moment rotation and domain wall motion in the three cases
are discussed.
