Ferromagnetism in Fe3−x−yNixGeTe2

Polycrystalline samples of Fe3−yGeTe2(0.08 ≤y≤ 0.29) and the solid solutions Fe3−x−yNixGeTe2(0.24 ≤x≤ 1.32; 0.14 ≤y≤ 0.41) were synthesized at 898–973 K in a resistance furnace and characterized by X-ray and neutron powder diffraction with Rietveld analysis (Fe3GeTe2type,P63/mmc,a= 402.665(3),c= 1632.820(14) pm forx= 0,y= 0.08). Fe3Ge layers with planar FeGe hexagons and additional iron atoms above and below the rings are separated by double layers of tellurium atoms. Fe3GeTe2is ferromagnetic belowTC= 230 K with magnetic moments aligned along thecaxis.TCdepends on the iron content and decreases with increasing iron vacancies continuously to 153 K in Fe2.71GeTe2. Further reduction ofTCis possible by nickel substitution until magnetic ordering is nearly absent in Fe1.33Ni1.32GeTe2. The suppression of the magnetic ordering is caused by random dilution of the magnetic iron atoms either by vacancies or by non-magnetic nickel atoms.