MAGNETIC INSTABILITY OF ULTRATHIN FCC FEXNI1-X FILMS

The ''invar effect'' in Fe3Nit-x alloys occurs when the Fe content app roaches 65%. At this point, the magnetization falls to zero, and a mar tensitic structural transformation from a fee to a bce lattice occurs. This paper addresses the question: ''What happens if the structural t ransformation is suppressed in an ultrathin alloy film?'' We present r esults to this effect, showing the variation of the magnetization with changing composition in ultrathin film grown on Cu(100). We find a ne w low-spin, ferromagnetic phase of matter, which is a sensitive functi on of the atomic volume.