Synthesis and Magnetic Moment of bct and fct-Fe-N

摘要

Giant magnetic moment exceeding a Slater-Pauling curve is predicted by theoretical calculation in α-Fe and γ-Fe, with increasing their unit-cell volume[1], and experimentally confirmed in γ-Fe, grown on Cu-Au by MBE, at low temperature[2]. However, γ-Fe that shows giant magnetic moment has low T{sub}c, and is hard to be applied to the actual magnetic devices such as a write pole of hard disk head. On the other hand, γ'-Fe{sub}4N is a stable phase of bulk material, that has fcc bone structure of Fe of which the octahedron position is occupied by N. Magnetic moment of γ'-Fe{sub}4N is small as 1.8μ{sub}B/Fe, but the T{sub}c is relatively high as 761K[3]. We can thus expect to obtain large magnetic moment with high T{sub}c with changing N content in fcc(fct) Fe lattice. Turning to α-Fe, which has high T{sub}c～1100K, its magnetic moment is potentially high. The present authors already clarified that a saturation magnetization of α"-Fe{sub}16N{sub}2, is about 240emu/g[4]. In addition, taking into account that α' or α" phases, bct bone structure of Fe, could be regarded as fct Fe lattice, we may say that α' and γ' phases of Fe-N are closely related to each other. Standing on these backgrounds, we expect to enhance the magnetic moment with maintaining high T{sub}c in bct and fct-Fe-N by increasing the unit-cell volume and N content. However, previous study showed that exceeding N addition poisons the volume effect of magnetic moment[5]. So we should enlarge unit cell volume with adding suitable N. In the present study, we synthesized bct and fct phases with various unit-cell volume by expanding in-plane lattice spacing and examined the volume effect of magnetic moment and T{sub}c for these phases.