Preparation, structural and magnetic properties and stability of interstitial Sm 2Fe 17-carbonitrohydrides

Abstract

Sm 2Fe 17-carbides, -nitrides, -hydrides, -carbonitrides, -carbohydrides, -nitrohydrides and -carbonitrohydrides were synthesized by reacting Sm 2Fe 17 powder with the appropriate gases (acetylene, nitrogen or hydrogen). Carbonation, nitrogenation and hydrogenation were performed at about 600 °C, 450 °C and 250 °C respectively. Low-carbon concentration carbides were prepared by conventional melting. The structural and magnetic properties were measured for each of the prepared compounds. Nitrogen and carbon can partially or fully occupy the 9(e) octahedral interstices. In addition to these, hydrogen can also partially occupy the 18(g) tetrahedral interstices. Interstitial carbon, nitrogen and hydrogen atoms cause an expansion of the lattice of the parent compound. Hydrogenation of the saturated Sm 2Fe 17-carbide or saturated Sm 2Fe 17-nitride causes preferential lattice expansion along the c-crystallographic direction. Hydrogen atoms cause the largest increase in saturation magnetization, followed by nitrogen and carbon atoms. The largest increase in the anisotropy field is caused by the nitrogen atoms followed by the carbon atoms. The hydrogen atoms cause a decrease in the anisotropy field. The nitrogen atoms cause the largest increase in the Curie temperature followed by the carbon and hydrogen atoms. Nitrogen atoms are very strongly bonded to the samarium atoms and weakly to the iron atoms, whereas carbon atoms are strongly bonded to both the samarium and iron atoms. This strong bonding makes the reversible removal of the nitrogen and carbon atoms impossible. However, hydrogen bonding is much weaker and therefore, hydrogen atoms can be absorbed and desorbed easily without any change in the Sm 2Fe 17 structure. Nitrogen and carbon atoms can replace the hydrogen atoms in the 9(e) sites.