Microstructure and magnetic properties of melt-spun Sm2Fe15-xCoxCr2C2 (x = 0-4) nanocomposite magnets

The amorphous formation ability, crystallization behavior, microstructure and magnetic properties of melt-spun and heat treated Sm2Fe15Cr2C2 magnets have been systematically studied using XRD, DSC, TEM and magnetic measurements. It has been found that the as-spun ribbons are comprised of a mixture of alpha-Fe, a small amount of 2 : 17 phase and an amorphous phase when the wheel speed is 17 ms and become pure amorphous when the wheel speed is increased up to 61 m/s. The coercivity is dramatically increased by subsequent annealing. A higher annealing temperature combined with a shorter annealing time leads to a higher coercivity and annealing at 900 degrees C for 1 min was found to give the highest coercivity of 12.1 kOe. XRD and TEM studies reveal that the microstructure of the annealed ribbon is composed of 2 : 17 carbide as the majority phase and a small amount of alpha-Fe as the minority phase. The average grain size at the optimum annealing was found to be about 35 nm for the 2. 17 and 60 nm for alpha-Fe. It is further found that a small amount of Co substitution for Fe not only increases the Curie temperature of the 2 : 17 carbides, but also significantly reduces the grain size of alpha-Fe to about 20 nm, leading to a much smoother hysteresis loop and a better temperature dependence of coercivity. (C) 1998 Elsevier Science B.V. All rights reserved.