Magnetic ordering in nitrides with the eta-carbide structure, (Ni,Co,Fe)2(Ga,Ge)Mo3N.

Compositions in the series Ni(2-x)Co(x)GeMo(3)N (0 < or = x < or = 2), Co(2)Ge(1-x)Ga(x)Mo(3)N (0 < x < or = 0.7), Co(2-x)Fe(x)GeMo(3)N (0 < or = x < or = 2), and Co(2-x)Fe(x)Ge(0.5)Ga(0.5)Mo(3)N (0 < or = x < or = 0.8) have been synthesized by the reductive nitridation of binary oxides and studied by appropriate combinations of magnetometry, transport measurements, neutron diffraction, and Mossbauer spectroscopy. All of these compositions adopt the cubic eta-carbide structure (a approximately 11.11 A) and show a resistivity of approximately 10(-3) Omega cm. No long-range magnetic order was observed in Ni(2-x)Co(x)GeMo(3)N, although evidence of spin freezing was observed in Co(2)GeMo(3)N. The introduction of gallium into this composition leads to the onset of antiferromagnetic ordering at 90 K in Co(2)Ge(0.3)Ga(0.7)Mo(3)N. The magnetic structure consists of an antiferromagnetic arrangement of ferromagnetic Co(4) groups, with an ordered magnetic moment of 0.48(9) micro(B) per cobalt atom. The same magnetic structure is found in Co(0.5)Fe(1.5)GeMo(3)N and Co(1.2)Fe(0.8)Ge(0.5)Ga(0.5)Mo(3)N. The former orders above room temperature with an average moment of 1.08(3) mu(B) per transition-metal site, and the latter at 228 K with an average moment of 1.17(4) micro(B) per site. The magnetic behavior of these compounds is discussed in terms of the electron count within each series.