Effect of nonstoichiometry on the transition from ferromagnetism to antiferromagnetism in the ternary indides Ce1.95Pd2+2xIn1-x and Ce2+xPd1.85In1-x

Single phase polycrystalline samples of the ternary indides Ce1.95Pd2+2xIn1 -x (0.05 less than or equal to x less than or equal to 0.23) and Ce2+xPd1.8 5In1-x (0.06 less than or equal to x less than or equal to 0.37) were synth esized and characterized by microprobe analysis and x-ray diffraction. The effect of the chemical composition on the magnetic properties was investiga ted by means of magnetization and specific-heat measurements as well as by neutron diffraction. The ternary indides crystallize in the parent Mo2FeB2 structure (space group P4/mbm) and form two branches of solid solutions due to different substitutional mechanisms. In the Pd-rich branch indium vacan cies at the 2a site are compensated by an excess of palladium located at an additional 4e site. In the Ce-rich branch the excess of cerium replaces in dium atoms at the 2a site. The magnetic properties are strongly influenced by the chemical composition. Excess of palladium favors antiferromagnetism of a sinusoidal modulated type with the propagation vector k approximate to [0.22,0,0] whereas excess of cerium induces ferromagnetism. The magnetic m oments in both cases are oriented parallel to the c axis.