Structure and magnetic properties of RFe13-xSix (R = Pr, Nd or Gd, x = 2.5-5)

RFe13-xSix (R = Pr, Nd and Gd) alloys with x = 2.5-5 have been synthesized and characterized in a magnetic field up to 17 kOe and in a temperature range 10-1173 K to ascertain whether they might be useful as high temperature, high-energy permanent magnet materials. It was found that a body-centered tetragonal (BCT) Ce2Ni17Si9-type structure forms in PrFe13-xSix alloys when x greater than or equal to 4. The Curie temperatures T-c of this BCT phase are in a range 50-90 K, higher than that of the corresponding PrCo13-xSix BCT phase (similar to 20 K). The PrFe13-xSix alloys with x greater than or equal to 4 show spin reorientation at cryogenic temperatures (15-47 K) and exhibit significant coercivity in loose powder samples below their spin-reorientation temperature. Using the information about the magnetization of LaFe13-xSix BCT alloys, one can estimate the moment of Pr ion in PrFe13-xSix alloys, It is found to be very close to that in PrCo13-xSix BCT alloys, around 2 mu(B)/atom. For R = Nd or Gd, the RFe13-xSix alloys occur only as mixtures of RFe2Si2, R(Fe,Si)(11) and Fe-Si. The Ce2Ni17Si9-type structure cannot be formed in these alloys even when x = 5. The low T-c for the PrFe13-xSix alloys precludes their use as a permanent magnet material, except perhaps at low temperature.