New Semi-Hard Magnetic Alloys of Co–Fe–Be System

Abstract

New semi-hard magnetic alloys, which have a square hysteresis loop and a low value of magnetostriction, are presented here. These alloys consist of about 90% Co, about 1% Be, and the balance Fe. We can attain a coercive force between 10 and 30 Oe by controlling the Be content. The Co content affects the stress sensitivity of the hysteresis-loop shape. One example is a tape 0.126 mm wide and 0.011 mm thick containing 88.5% Co, 1.3% Be, and 10.2% Fe, finally annealed at 800°C for 10 sec. This tape exhibits a coercive force of about 30 Oe, a squareness ratio of about 0.9, and very small change in the hysteresis-loop shape with 20-kg/mm2 tensile stress. In a sample containing more than 0.7% Be, CoBe precipitates and the grain size is much smaller than in a sample without Be. This fact contributes to the increase of coercive force with Be content. Moreover, the drawn wire has a 〈111〉 fiber texture, and the rolled-flat tape has a {110} 〈111〉 texture. These textures do not change until at least 900°C annealing temperature, and the squareness ratio of the hysteresis loop along the wire or the tape axis remains high. One of these alloys is now used for information storage in a computer memory device named CTM (Composite Tape Memory).