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 less than or equal to 2.5 and x greater than or equal to 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 (T-C 394 K), an average magnetic moment per Fe atom constitutes 1.78 mu(B) 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 K-1 does not exceed 10(6) erg/cm(3). (C) 2003 Elsevier Science B.V. All rights reserved.