Studies of Mossbauer spectra for nitrides RTiFe11Nx (R=Y, Nd, Sm, Gd and Er)

Abstract

Magnetic properties and 57Fe Mossbauer spectra for the nitrides, RTiFe11Nx, and for their parents RTiFe11 (R=Y, Nd, Sm, Gd and Er) have been studied. The Curie temperatures of RTiFe11Nx increase by 135-200 degrees C over those for RTiFe11. The maximum Curie temperature is 745 K for GdTiFe11Nx. The Fe atomic moments at room temperature are 1.84 mu B and 1.52 mu B for YTiFe11Nx and YTiFe11, respectively. Mossbauer spectra of the nitrides are fitted by using seven sets of subspectra, needed because the N atoms affect the hyperfine parameters. As compared to RTiFe11, the average hyperfine field increases by 5-9 T and the average isomer shift by 0.10-0.18 mm s-1 for RTiFe11Nx. For most of the RTiFe11 series and their nitrides, the average hyperfine fields have a linear relationship with (gR-1) JR which can be understood with the RKKY theory. The core electron polarization field, Bcp, 4s electron polarization field, B4s, and transfer field, Bmp, have been analysed and compared for the Y compound. The N atoms bring about an increase in magnitude of Bcp and Bmp and a decrease in magnitude of B4s, which leads to an average increase of about 9 T in magnitude for the hyperfine field of YTiFe11Nx as compared to YTiFe11. The proportionality coefficient between the average hyperfine field and the Fe moment for YTiFe11Nx deviates far from the normal value of 15T mu B-1. This is attributed to a very large increase in the total conduction-electron polarization field.