LaFe_13-x-yM_xSi_yN₃ compounds (M = Mn) were synthesized by flowing ammonia over intermetallic precursors at 623 K for 4 hours. The nitrides were characterized by room temperature powder X-ray diffraction, magnetic thermogravimetry (mTGA), differential scanning calorimetry (DSC), and magnetization measurements. The nitrides derived from Si-poor (y ≤ 3) cubic intermetallics retain the NaZn₁₃-type crystal structure and the lattice parameters, a, of the synthesized trinitrides increase by ~3 % compared to the precursors. The nitrogenation increases ferromagnetic ordering temperature by approximately 200 K when compared with the corresponding nitrogen-free NaZn₁₃-type phases, but unlike those of the latter, T_Cs of the nitrides are independent of the Fe/Si ratio. Partial substitution of Fe with Mn lowers T_C of the trinitride similarly to the non-nitrogenated precursors. The magnetic ordering transitions in the nitrides are broad, resulting in rather weak magnetocaloric effects peaking at -2.0 J/Kg K for a 0 to 5 T magnetic field change. The nitrides are stable below 750 K, but they begin to lose nitrogen above this temperature, fully decomposing above 1050 K.
Ames Laboratory is operated for the U.S. Department of Energy (DOE) by Iowa State University under Contract No. DE-AC02-07CH11358. This work was supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences of the U.S. DOE.