Anisotropic behavior of magnetic and transport properties in CePdSb and CePtSb

Measurements of resistivity rho, Hall coefficient R-H, magnetic susceptibil ity chi, magnetization, specific heat C and magnetoresistance have been per formed on the hexagonal ferromagnets CeTSb (T = Pd,Pt) and the isostructura l compounds LaTSb using single crystalline samples. Strong anisotropy in rh o, rho(c) > rho(a), was observed for both the Ce compounds as well as the L a compounds. However, R-H(T) for CeTSb does not exhibit strong anisotropy b etween H//a and H//c. The anisotropic behavior of chi(T) for the Ce compoun ds is well reproduced by the crystalline electronic-field model. The analys is of chi(T) suggests that the ferromagnetic exchange interaction along the c axis in CePdSb is much stronger than that in CePtSb. Magnetization measu rements reveal that the saturated magnetic moments of 1.32 mu(B) and 0.91 m u(B) for CePdSb and CePtSb lie within the c plane in the ferromagnetic stat e. The C(T) for CePdSb shows a clear jump at T-C = 17.5 K in addition to a broad peak around 10K. These results suggest that one dimensional magnetic order along the c axis occurs in CePdSb at T-C = 17.5 K and three-dimension al order develops only below 10 K. It is found that rho(c) increases below 8 K and 6 K for CePdSb and CePtSb, respectively, and R-H(H//a; I//c) also i ncreases below 10 K for both compounds. Unlike usual ferromagnets, the tran sverse and longitudinal magnetoresistances in the ferromagnetic states are largely positive for H//a. These unusual transport properties may be ascrib ed to the anomalous spin dynamics in the ferromagnetic state of the present systems.