Magnetism and phase relations of the PrAl2CaAl2, GdAl2CaAl2 systems

The magnetic properties and phase relations of the ternary systems Pr_1?xCa_xAl₂ and Gd_1?xCa_xAl₂ are reported. The first system exhibits complete miscibility whereas the second shows a miscibility gap extending from x = 0.5 to 0.8. The ternaries were examined magnetically to ascertain whether antiferromagnetism could be produced by replacing the trivalent rare earth ion with divalent Ca. Results for the (Pr, Ca)Al₂ system give some indication that the exchange changes sign when 80% or more of the Pr is replaced by Ca. The α-phase (Gd-rich) alloys in the (Gd,Ca)Al₂ system are ferromagnetic with Curie temperatures only modestly reduced from that of GdAl₂. The β-phase (Ca-rich) alloys in this system are paramagnetic to 4.2°K. The evidence suggests that PrAl₂ and CaAl₂ are electronically similar in regard to band structure and both differ in band structure from GdAl₂.