Magnetic, X-ray diffraction, and Mössbauer spectroscopy studies of Nd₂Fe₁₅Ga₂C_x magnets

X-ray diffraction patterns of Nd₂Fe₁₅Ga₂C_x (0 ≤ x ≤ 2) show that all the alloys studied have the Th₂Zn₁₇ rhombohederal structure. The lattice parameters and the unit cell volume are found to increase linearly with increasing carbon concentration. Structural measurements on magnetically aligned powder samples show that the samples studied possess magnetic anisotropy with a basal easy axis. Magnetization measurements at 5K and at room temperature show that all samples under investigation are ferromagnetic, and the saturation magnetization increases with increasing x, reaching a maximum at x = 1, and then decreases slowly for larger values of x. Mössbauer spectra show that all the samples are magnetically ordered at room temperature and the average hyperfine field behaves similar to the saturation magnetization, where it reaches a maximum of 242 kOe for x = 1. The isomer shift is negative and it increases with increasing C concentration. The results are explained in terms of the volume expansion and the magnetovolume effects.