Constitution, structural chemistry and magnetism of the ternary system Ce-Ag-Ge

Phase relations have been established for the Ce-Ag-Ge system at 850 degree s C by means of X-ray diffraction, light optical microscopy, and quantitati ve electron probe microanalysis, Phase equilibria are characterized by the existence of extended solid solutions of Ce(AgxGe1-x)(2-y) (ThSi2 type), Ce (Ag1-xGex)(1-y) and Ce(Ag1-xGex)(2-y) (unknown structure type). New ternary compounds were found to exist: Cesimilar to 7Agsimilar to 8Gesimilar to 5 (unknown structure), Cesimilar to 6Agsimilar to 5Gesimilar to 9 (unknown st ructure), Ce3Ag4Ge4 (Gd3Cu4Si4 type), and Ce(AgxGe1-x)(2) (AIB(2) type). Ge /Si substitution was investigated for the alloy systems CeAg-Si,Ge,, (CaIn2 type for x < 0.67 and LiGaGe type for x greater than or equal to 0.67) and CeAgx(SiyGe1-y)(2-x) (AIB(2) type). Magnetic behavior was studied from sus ceptibility and magnetization measurements down to 1.7 K and employing magn etic fields up to 5 T. In contrast to earlier descriptions of CeAgGe to ord er antiferromagnetically below 4.8 K, the authors' susceptibility and magne tization measurements revealed rather a soft ferromagnetic nature below 6.8 K. Substitution of Ge by Si, x(Si) = 0.1, 0.33, 0.5, 0.67, and 0.75, enhan ces the ferromagnetic interactions. The AIB(2)-type alloys, CeAg0.67Ge1.33 and CeAgGe0.84Si0.16 showed soft ferromagnetism with Curie temperature (T-C ) = 7.5 and 8.3 K, respectively. Starting from ferromagnetic binary CeGe2 ( ThSi2-y type, T-C = 7.2 K) replacement of Ge by Ag retains the ferromagneti sm below 8 K for x(Ag) = 0.08, but changes to antiferromagnetism with order ing (Neel) temperature T-N = 9 K for x(Ag) = 0.13, For CeAg2Ge2 (ThCr2Si2 t ype) the antiferromagnetic type of order is confirmed, but with lower order ing temperature, (T-N = 4.5 K) than derived earlier. Ce,Ag,Ge, (Gd,Cu,Ge, t ype) exhibits spin-glass behavior below 7 K, Complex magnetic properties we re encountered for Cesimilar to 6Agsimilar to 5Gesimilar to 9 (Cesimilar to 6Agsimilar to 5Gesimilar to 9 type) with two subsequent phase transitions at T-N = 8.5 K followed by T-C = 6.9 K.