TERNARY AND QUATERNARY RARE-EARTH COBALT MAGNETIC-MATERIALS WITH LOW REVERSIBLE TEMPERATURE COEFFICIENTS

Permanent magnets made from SmCo5 exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per degree between -100 and +200°C. For special applications in precision instruments such as gyros and accelerometers it is desirable to reduce considerably the temperature coefficient of magnetization. Earlier studies have indicated that good temperature-compensated magnets may be prepared by replacing a part of Sm in SmCo5 with other heavy rare earth atoms such as Gd, Dy, Ho and Er. In the present study a number of compositions of the type SmxRl-xCo5 [R = Gd, Dy, Ho, Er, Tm, Yb, and Ti], (SmGd) Co5-yFey and Sm0.6 (R′Gd)0.4Co5 [R′ =Dy, Ho, Er] were prepared and examined by a number of techniques. X-ray diffraction patterns indicated the formation of essentially single phases in many of these compositions. Saturation magnetization, remanance, coercive force, anisotropy field and energy product of these materials at room temperature are reported. Magnetization measurements were performed in the temperature range -100 to +200°C and the values of α (reversible temperature coefficient of magnetization) were determined. As an illustration, for a material of composition Er0.2Sm0.8Co5.2 we observed the following results: 4πMs=11.6 kG, Br=11.1 kG, H ci =8.6 kOe and (BH)max = 17 MGOe at room temperature. The values of α observed are 0.025 between 150-225 K, 0.008 between 225-300 K and -0.009 between 300 and 375 K. Results for other compositions and their systematic trends are discussed.