Effect of Fe substitution on structural and magnetic properties of Pr₂Co_7-xFe_x compounds

¹ Laboratoire Matériaux Organisation et Propriétés, Faculté des Sciences de Tunis, Université Tunis El Manar, 2092 Tunis, Tunisia
² CMTR, ICMPE, UMR7182, CNRS – Université Paris 12, 2-8 rue Henri Dunant F-94320 Thiais, France

^a e-mail: FERSI@glvt-cnrs.fr

Abstract

This work focuses on the synthesis, structure, and magnetic properties of Pr-Co-Fe compounds. Our previous study of Pr₂Co₇ alloys with high coercivity is shown that for samples annealed at Ta= 800 °C, the main phase is hexagonal of the Ce₂Ni₇ type structure. This leads to the formation of a magnetically hard Pr2Co7 phase; the coercivity being equal to 18 kOe at 293 K and 23 kOe at 10 K and important saturation magnetization. These performances are due to the combination of the complementary characteristics of 3d-itinerant and 4f-localized magnetism of Co and Pr, respectively. Its Curie temperature is about 600 K. The aim of this study is to follow the effect of partial substitution of Co by Fe on Pr₂Co_7-xFe_x structural and magnetic properties, where x =0.25, 0.50, 0.75 and 1. These compounds were synthesized by mechanical alloying. The Rietveld analysis of DRX shows that these intermetallics, annealed at Ta = 700 °C, adopt mainly hexagonal Ce₂Ni₇ type structure with P6₃/mmc group space. Moreover, it points out a lattice expansion along the c axis after Fe substitution for Co. Furthermore, these hexagonal phases possess magnetic properties more attractive than Pr₂Co₇, the Curie temperatures are higher than Pr₂Co₇ ones and the highest is obtained for x = 0.5 where TC = 760 K. This increase is due to the well-known electronic effect that invokes the reduction of antiferromagnetic coupling. These phases are particularly promising for permanent magnet applications.