Magnetic and transport properties of the pseudobinary systemsCe(Fe1−xCox)2and(Ce1−yScy)Fe2

Abstract

We studied the dilute substitution effect on magnetic and transport properties in an unstable ferromagnet ${\mathrm{CeFe}}_{2}$ with a C15 cubic Laves-phase structure. In the Co substitution system $\mathrm{Ce}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}$ with $xl~0.10,$ while the Curie temperature ${T}_{C}$ decreases with increasing the Co concentration, an antiferromagnetic ordering appears in the low temperature region for $x\ensuremath{\geqq}0.05,$ and the transition temperature ${T}_{0}$ from ferromagnetic to antiferromagnetic states monotonously increases with increasing the Co concentration. On the other hand, in the Sc substitution system $({\mathrm{Ce}}_{1\ensuremath{-}y}{\mathrm{Sc}}_{y}){\mathrm{Fe}}_{2}$ with $yl~0.10,$ 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 $\mathrm{Ce}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2},$ whereas a ferromagnetic ground state is stabilized in $({\mathrm{Ce}}_{1\ensuremath{-}y}{\mathrm{Sc}}_{y}){\mathrm{Fe}}_{2}.$ These results indicate that the $\mathrm{Fe}3d--\mathrm{Fe}3d$ ferromagnetic exchange interaction and the antiferromagnetic spin correlation arising from the $\mathrm{Ce}4f--\mathrm{Fe}3d$ hybridization compete in ${\mathrm{CeFe}}_{2},$ and the enhancement/depression of the $4f\ensuremath{-}3d$ hybridization effect might make the ferromagnetic ground state in ${\mathrm{CeFe}}_{2}$ unstable/stable. Furthermore, $\mathrm{Ce}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}$ exhibited a negative giant magnetoresistance reaching about $\ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}=\ensuremath{\sim}60--65%$ 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.