Nitrogen gas-solid reaction process and basic magnetism of the interstitially modified rare-earth 3d transition-metal nitrides R2Fe17N3 (R=Y, Ce, Nd, Sm) and Y2Co17N3

In this paper, we present our recent results of studies of the nitrogen absorption process, magnetization measurements, and neutron powder-diffraction measurements for interstitially modified nitrides R2Fe17N3 (R=Y, Ce, Nd, and Sm) and Y2Co17N3. (1) The studies of nitrogen absorption rates in the Sm2Fe17 under various N2-gas pressure up to 6 MPa indicated that the nitrogen absorption into grain interior is promoted by diffusion of nitrogen atoms under low N2-gas pressure, while under high N2-gas pressure, the nitrogen absorption is promoted by the grain growth of fully nitrogenated phase Sm2Fe17N3 rather than the diffusion, making high-pressure nitrogenation effective for synthesizing high-quality nitrides. (2) The high-field magnetization measurements of the Nd2Fe17 and Nd2Fe17N3 single crystals at 4.2 K indicated that interstitial modification of nitrogen atoms gives rise to a strong enhancement of crystalline electric field (CEF) acting on R atoms, leading to almost three times larger CEF-parameter A20 upon nitrogenation. (3) Neutron powder-diffraction studies of Y2Fe17 and Y2Fe17N3.1 with rhombohedral structure indicated that the N atoms fully occupy at the 9e site. The introduction of N atoms into Y2Fe17 brought such a strong modification in the Fe magnetic moment that the moment of the 18f-Fe atoms being the nearest to the 9e-N atoms is the smallest, whereas the 6c-Fe and/or 18h-Fe atoms being relatively farther from the 9e-N atoms have the largest moments at 10 K. The results obtained are discussed on the basis of the calculated electronic band structures