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Abstract:
Alloys with the composition RECo13−x Ga x (x≤4.4) have been prepared by arc melting and subsequent annealing for 120 h at 800 °C in evacuated, Mo‐lined silica capsules. The Ce,Pr compounds were found to decompose at 900 °C, and no compound formation was observed for the Gd,Sm members in the investigated temperature range from 600 to 900 °C. For the LaCo13−x Ga x system an extended homogeneity region was observed crystallizing with the cubic NaZn13 type for concentrations x<2.5. For concentrations x>2.5 x‐ray powder diffraction analysis for all the rare earth members proved isotypism with a tetragonal NaZn13 ‐derivative structure, whose crystal symmetry and atom sites were consistent with the Ce2Ni17Si9 type of structure. From magnetization experiments in the range from 5 to 1300 K a generally hard‐magnetic behavior was observed for all the RE alloys with tetragonal symmetry and ferromagnetic ordering occurs below T c <650 K. Curie temperatures in the LaCo13−x Ga x system monotonically drop from T c =1290 K for cubic LaCo13 to T c =145 K for tetragonal LaCo8.7Ga4.3. For the Ce compound ferrimagnetic behavior is suggested. Assuming trivalent rare earth ions, effective paramagnetic moments of the Co atoms decrease as a function of x from 5.9 μ B at x=3.1 to ∼3 μ B at x=4.3.
