Intrinsic magnetic properties of R2Fe17CyNx compounds: (R=Y, Sm, Er, and Tm)

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Abstract
Samples of R 2Fe17C y N x (R=Y, Sm, Er, Tm) were prepared by arc melting appropriate amount of R, Fe, and C, vacuum annealing at 1373 K and finally annealing at 740 K in nitrogen for 10 h. The magnetic properties of these compounds were investigated by means of ac initial susceptibility,magnetization measurements, and x‐ray diffraction. The thermal stability of the nitride phase was studied by differential scanning calorimetry. It was found that, when heated above 600 K, R 2Fe17C y N x irreversibly decomposes N which is irrespective of the carbon concentration and rare‐earth element. The Curie temperatures of R 2Fe17C y N x are independent of the carbon concentration and are approximately 400 K higher than those of the corresponding pure R 2Fe17compounds. However, the Curie temperatures cannot be correlated to the composition x of the initial R 2Fe17C y N x compounds at room temperature because some N was lost during the heating to T c . In the Er and Tm compounds spin reorientation transitions were found, marking the change of the easy magnetization direction from the c axis to the basal plane with increasing temperature. The Tm compounds show an additional magnetic transition at low temperatures (below 40 K). A coexistence of the hexagonal and the rhombohedral structural modifications was found in Er2Fe17C y N x when y<1.5, characterized by two different spin reorientation temperatures. The anisotropy fields of Sm2Fe17C y N x are higher than that of Sm2Fe17N x . Indications of a magnetic phase transition were found also in Sm2Fe17C0.7N x and Sm2Fe17C0.9N x .