Effect of substitution of Zr on the magnetic properties of R2Co17 (R = Ce and Sm)

The ternary systems Ce₂Co_17?xZr_x and Sm₂Co_17?xZr_x have been studied to ascertain the effect of Zr substitution on the magnetic properties. X-ray diffraction experiments show that single phase materials can be obtained only in the range of x ≤ 1 and that Zr stabilizes the hexagonal Th₂Ni₁₇ structure. The unit cell volume is found to increase by substitution of Zr. The Curie temperature T_c decreases monotonically with increasing x at an approximate rate of 100 and 90 deg/atom for the Ce and Sm systems, respectively. The saturation magnetic moments also decrease monotonically with increasing x for both the systems. The rate of decrease is larger than that expected as a simple dilution. The anisotropy fields H_A are significantly increased by Zr substitutions for both the systems, reaching 70 and 200 kOe at 77 K in the cases of Ce₂Co₁₆Zr₁ and Sm₂Co₁₆Zr₁, respectively. Among all the substituents studied until now, Zr seems to be the most effective for permanent magnet applications. Crystallographic and magnetic characteristics indicate that Zr replaces Co when the ternaries are formed.