New Low-Magnetostrictive Permanent-Magnet Alloys

Abstract

Some present day applications require magnetic materials to be used while being stressed in a complex manner. Of current interest would be a ductile material that has a square hysteresis loop, a magnetic saturation of approximately 18 000 G, a coercive force in the range of 10 to 20 Oe, and, in addition, a very low value of magnetostriction. It has recently been found that some of the face‐centered cubic alloys of the Co–Fe–Au system fulfill these requirements. The level of coercive force is controlled by gold additions and by precipitation aging. Detailed study on an alloy of 82% Co, 12% Fe, and 6% Au showed that the coercive force is increased by increasing the degree of cold work prior to the aging treatment. Furthermore, the aging temperature for the peak value of coercive force varied greatly with the degree of prior cold work. For wire initially solution heat‐treated at 1050°C, the coercive force peak occurred at an aging temperature of 775°C; whereas for wire initially cold‐drawn 97.5%, the peak occurred at 550°C, a decrease of 225°C. Thus, the kinetics of precipitation is greatly facilitated by prior cold work in this alloy. The 82% Co, 12% Fe, and 6% Au alloy exhibits a very low strain sensitivity, the coercive force changing only a few percent under a tensile stress of 5 kg/mm². A squareness ratio better than 0.85 is obtained after appropriate treatment.