INVESTIGATION OF THE TRANSITION FROM FERROMAGNETIC TO ANTIFERROMAGNETIC ORDER IN THE CEMN2(GEXSI1-X)2 SYSTEM

Samples in the alloy system CeMn2(GexSi1-x)2 exhibit a crossover from antiferromagnetic ordering for CeMn2Si2 to ferromagnetic ordering for CeMn2Ge2 as a function of concentration. The low temperature behavior of samples in the range 0.0 less-than-or-equal-to x less-than-or-equal-to 1.0 using the techniques of dc magnetization, ac susceptibility, and thermal expansion were studied. From this we have determined the magnetic phase diagram which shows four concentration regions of qualitatively different low temperature behavior. Increasing substitution of Ge for Si in CeMn2Si2 shows a depression of T(N) and the gradual development of ferromagnetic order at T almost-equal-to 305 K. For 0.42 less-than-or-equal-to x less-than-or-equal-to 0.60 there is a clear ferromagnetic transition at T almost-equal-to 305 K followed by a sharp drop in magnetization at lower temperatures. For all samples ac susceptibility shows a sharp peak near 300 K indicating the onset of magnetic order at that temperature. Neither ac susceptibility nor thermal expansion measurements show clear anomalies at T(N) below T(c). There is evidence of mixed magnetic behavior for these samples.