Filing Date: 2002-04-03.-- Priority Data: GB 0108373.2 (2001-04-03)A Co-Fe-Mn-B-Si alloy suitable for use in the manufacture of micro wires which exhibit bistable magnetic behaviour, the alloy comprising: Iron from 2 to 15 at . % Manganese from 3 to 7.5 at . % Boron from 12 to 16 at. % Silicon From 8 to 14 at . % Cobalt - balance Wherein the alloy exhibits an essentially rectangul ar magnetisation loop.