Magnetic and transport properties or the pseudobinary systems Ce(Fe1-xCox)2 and (Ce1-ySc)Fe2 -: art. no. 054405

We studied the dilute substitution effect on magnetic and transport properties in an unstable ferromagnet CeFe2 with a C15 cubic Laves-phase structure. In the Co substitution system Ce(Fe1-xCox)(2) with x less than or equal to0.10, while the Curie temperature T-C decreases with increasing the Co concentration, an antiferromagnetic ordering appears in the low temperature region for x greater than or equal to0.05, and the transition temperature T-o from ferromagnetic to antiferromagnetic states monotonously increases with increasing the Co concentration. On the other hand, in the Sc substitution system (Ce1-yScy)Fe-2 with y less than or equal to0.10, both the Curie temperature T-c and saturation magnetization M-s at 4.2 K gradually increase with increasing the Sc concentration. Despite the decrease in lattice parameter upon substitution in both the systems, an antiferromagnetic ground state is stabilized in Ce(Fe1-xCox)(2). whereas a ferromagnetic ground state is stabilized in (Ce1-yScy)Fe-2. These results indicate that the Fe 3d-Fe 3d ferromagnetic exchange interaction and the antiferromagnetic spin correlation arising from the Ce 4f-Fe 3d hybridization compete in CeFe2, and the enhancement/depression of the 4f-3d hybridization effect might make the ferromagnetic ground state in CrFe2 unstable/stable. Furthermore, Ce(Fe1-xCox)(2) exhibited a negative giant magnetoresistance reaching about Delta rho/rho = similar to 60-65% at 4.2 K, which is accompanied by a metamagnetic transition from antiferromagnetic to ferromagnetic states. The giant magnetoresistance effect is originated from the reconstruction of Fermi surface due to the collapse of the superzone gap after the metamagnetic transition.