Structural, magnetic and exchange interaction studies on R2Fe17-xGax (R = Tm, Er and Sm) compounds

A detailed investigation of the structure and magnetic properties of R2Fe17 -xGax (R = Tm, Er and Sm and x = 0-7) was carried out by means of powder X- ray diffraction, magnetization and AC magnetic susceptibility measurements. With increasing Ga content, a structural transformation from hexagonal Th2 Ni17-type structure to rhombohedral Th2Zn17-type structure is observed in c ompounds Er2Fe17-xGax (x = 0-7) and Tm2Fe17-xGa, (x = 0-7). The compounds S m2Fe17-xGax (x = 0-7) crystallize in rhombohedral Th2Zn17-type structure. T he Curie temperature increases in the initial Ga concentration range, reach es a maximum and then decreases at higher Ga concentration. The exchange in teraction parameter J(FeFe) reaches a maximum and then decreases whereas th e value of J(RFe) is almost independent of Ga concentration. X-ray diffract ion measurements on magnetically aligned powder samples show a uniaxial ani sotropy for compounds with at x = 2, 3 and 4 in the Sm2Fe17-xGax series whe reas, it was observed for x = 7 in the Tm2Fe17-xGax compounds. (C) 2000 Els evier Science B.V. All rights reserved.