Synthesis and magnetic properties of LaFe13-x-yMxSiyN3 nitrides

Abstract

Single-phase LaFe13-x-yMxSiyN3 compounds (M = Mn) were synthesized by subjecting intermetallic precursors to the ammonia flow at 623 K for 4 h. The nitrides derived from Si-poor (y ≤ 3) cubic intermetallics retain the NaZn13-type crystal structure and show considerable (~3 %) lattice expansion compared to the nitrogen-free materials. The temperatures of the magnetic ordering transitions, all of which are second order, increase by ~ 200 K as a result of nitrogenation, and all nitrides exhibit rather weak and broad magnetocaloric effects. The nitrides are stable below 750 K, but they begin to lose nitrogen above this temperature, fully decomposing above 1050 K. The nitrogenation of the tetragonal LaFe9Si4 results in the decomposition of the intermetallic phase and formation of the Fe3N compound together with unidentified amorphous phase(s).