MAGNETIC AND STRUCTURAL CHARACTERISTICS OF PRCO13-XSIX ALLOYS AND THEIR NITRIDES

PrCo13-xSix alloys with 0 less than or equal to x less than or equal to 4.5 have been synthesized and studied at temperatures from 10 to 1273 K and in fields up to 17 kOe. The structure and magnetic properties of the alloys vary significantly with changes in Si content x. In the alloys with x = 0, TMA and XRD studies show the phases present to be Pr2Co17 and Co. For x = 1.5 or 2.0, the alloys are essentially single-phase fcc materials (NaZn13 structure type). At larger values of x the ternary alloy formed in a bct structure (Ce2Ni17Si9 structure type). Replacement of Co by Si in PrCo13 results in a drop in T-C from 1318 K (for LaCo13) to similar to 900 K for fcc Pr(Co,Si)(13) alloy and to similar to 20 K for bct Pr(Co,Si)(13) alloys. There is also a large drop in magnetization from 104.6 emu/g for the alloy with x = 1.5 to 19.2 emu/g for the alloys with x = 4.0. A bct alloy (x = 3.5) showed negligible magnetic anisotropy. Si doping sharply reduces the Co moment. Si doping also reduces the Pr moment to 1.5 mu(B) (fcc alloys) and to 1.8 mu(B) (bct alloys). Nitrogenation fails to improve Pr(Co,Si)(13) alloys as permanent magnet materials.