Nitrogen gas–solid reaction process and basic magnetism of the interstitially modified rare-earth3dtransition-metal nitridesR2Fe17N3(R=Y,Ce,Nd,Sm)andY2Co17N3

Abstract

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 ${R}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$ $(R=\mathrm{Y},$ Ce, Nd, and Sm) and ${\mathrm{Y}}_{2}{\mathrm{Co}}_{17}{\mathrm{N}}_{3}.$ (1) The studies of nitrogen absorption rates in the ${\mathrm{Sm}}_{2}{\mathrm{Fe}}_{17}$ under various ${\mathrm{N}}_{2}$-gas pressure up to 6 MPa indicated that the nitrogen absorption into grain interior is promoted by diffusion of nitrogen atoms under low ${\mathrm{N}}_{2}$-gas pressure, while under high ${\mathrm{N}}_{2}$-gas pressure, the nitrogen absorption is promoted by the grain growth of fully nitrogenated phase ${\mathrm{Sm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$ rather than the diffusion, making high-pressure nitrogenation effective for synthesizing high-quality nitrides. (2) The high-field magnetization measurements of the ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{17}$ and ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$ 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 ${A}_{2}^{0}$ upon nitrogenation. (3) Neutron powder-diffraction studies of ${\mathrm{Y}}_{2}{\mathrm{Fe}}_{17}$ and ${\mathrm{Y}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3.1}$ with rhombohedral structure indicated that the N atoms fully occupy at the $9e$ site. The introduction of N atoms into ${\mathrm{Y}}_{2}{\mathrm{Fe}}_{17}$ brought such a strong modification in the Fe magnetic moment that the moment of the $18f\ensuremath{-}\mathrm{Fe}$ atoms being the nearest to the $9e\ensuremath{-}\mathrm{N}$ atoms is the smallest, whereas the $6c\ensuremath{-}\mathrm{Fe}$ and/or $18h\ensuremath{-}\mathrm{Fe}$ atoms being relatively farther from the $9e\ensuremath{-}\mathrm{N}$ atoms have the largest moments at 10 K. The results obtained are discussed on the basis of the calculated electronic band structures.