Impact of carbon insertion on the microstructure and magnetic properties of nanocrystalline Pr2Co7 alloys

Highlights: •High-energy milling technique. •X-ray diffraction using the Rietveld method. •Transmission electron microscopy. •Curie temperature and coercivity. •Extrinsic and intrinsic properties of carbides. -- Abstract: In this work, we have investigated a multi-scale study of the Pr2Co7 carbides. The Pr2Co7Cx compounds (where x = 0, 0.25, 0.5, 0.75, 1) were synthesized by melting pure components in stoichiometric proportion in an arc furnace followed by high ball energy milling and annealing at different temperatures. The Pr2Co7Cx compounds was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Rietveld analysis of XRD diagrams showed that the nanocrystalline Pr2Co7Cx compounds annealed at T = 973 K, mainly adopt a hexagonal Ce2Ni7 type structure with P63 mmc space group. We have shown that the lattice parameters a, c, and cell volume V increased with increasing x content. TEM images showed that the addition of carbon refined the microstructure. In fact, it was observed that the mean grain size decreased from about 40 nm, when x = 0, to 15 nm when x = 1. A systematic study of the intrinsic magnetic properties of these alloys was done and showed the insertion of carbon yields enhancement of the Curie temperature by 130 K for x = 1. This is due to the hypothesis of magnetovolumic and electronic effects on these properties. All thes studied compounds are ferromagnetic. The saturation moment μs of nanocrystalline Pr2Co7Cx increases from 8.3 to 11.6 μB/f.u with increasing C content from x = 0 to 1. In addition, the study of extrinsic magnetic properties, shows that the coercivity of the nanocrystalline Pr2Co7Cx compounds decreases with increasing carbon content. The best overall properties including a coercivity Hc of 10.5 kOe and a maximum energy product (BH)max of 11.5 MGOe for x = 0.25, have been obtained at room temperature. These magnetic properties are suitable for hard magnetic applications