La-substitution effects on multisite Ce compound CePtGe₂

The CePtGe₂ compound, which shows antiferromagnetic transition at Neel temperature T_N = 3.8 K, has two crystallographically inequivalent Ce sites. Recently, the coexistence of a localized f-electron state at one of two Ce sites and an itinerant heavy f-electron state at the other Ce site has been suggested. In this study, we have prepared polycrystalline samples of (Ce_1-xLa_x)PtGe₂ (x = 0 ∼ 0.2) and have measured their electrical resistivity and magnetization. The specific heat for x = 0.2 has been measured also. With increasing x, the downward bending of the temperature dependence of the resistivity and the cusp-type anomaly in the susceptibility associated with T_N shift to lower temperatures with a linear extrapolation of T_N directing to 0 K at x ∼ 0.5. Also, the saturation magnetization decreases linearly with increasing x, pointing to the disappearance of magnetic moments at the same La concentration. These results indicate that only the Ce ions with the localized f-electron are substituted by La ions. On the other hand, the transition from the antiferromagnetic state to the ferromagnetic-like polarized magnetic state at a very weak magnetic field, which is comparable to that of conventional Ferrite magnets, was realized via the La-substitution. (author)