Crystal structure of novel ferromagnetic LaFe13-xGaxC compounds

The addition of a small amount of carbon stabilizes NaZn13-type compounds in La-Fe-Ga system. New LaFe13-xGaxC compounds have been synthesized. The crystal structure-type depends on the Ga concentration. Compounds with x≤2.5 and x≥7 crystallize in the cubic NaZn13-type structure. Compounds with 2.5<x<7 have a tetragonal crystal lattice (space group I4/mcm) presenting a superstructure of a new type on the basis of NaZn13. The best long-range order is observed in compounds with x=3.5-4. Compounds are ferromagnets with Curie temperatures 120-400 K. For LaFe9.5Ga3.5C (TC=394 K), an average magnetic moment per Fe atom constitutes 1.78 μB at 2 K. The easy magnetization direction lies close to the basal plane of a tetragonal lattice at all temperatures. A value of the magnetocrystalline anisotropy constant K1 does not exceed 106 erg/cm3