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Experimental results of the magnetization ͑M͒, specific heat ͑C p ͒, electrical resistivity ͑͒, magnetoresistance ͑MR͒, and thermoelectric power ͑S͒ are presented for single crystals of the tetragonal UCo 0.5 Sb 2 compound. Anomalies in the M(T), ͓C p (T)͔, (T), S(T) dependencies have allowed us to establish that UCo 0.5 Sb 2 undergoes a long-range ferromagnetic ordering at T C = 64.5͑2͒ K. The temperature dependence of the magnetization measured fairly far below T C might be explained by considering both types of magnetic excitations: i.e., the spin-wave-and Stoner-type excitations. The M(T) dependence is well represented by the relation 1 − M͑T͒ / M s = BT 3/2 + B 1 T 3/2 exp͑−⌬ / T͒ with the determined spin-wave stiffness constant D ϳ 100 meV Å 2 and a Stoner gap ⌬ =69͑2͒ K. The behavior of the electrical resistivity below about T C / 2 is discussed in terms of the electron scattering on magnons with a dispersion relation E q = ⌬ + Dq 2 and the two-dimensional weak localization effect described by a Ϫln T dependence. Negative magnetoresistance is observed over a wide range of temperatures below 150 K. The relative large field and temperature changes in the transverse MR around T C are thought to be due to the ferromagnetic order or/and damped critical fluctuations by the applied fields. Below 40 K the magnetoresistance behavior may be understood on the basis of the predominant elastic scattering predicted for two-dimensional systems with the weak localization effect. The thermoelectric power data indicate UCo 0.5 Sb 2 to be a p-type material with a moderate S value of ϳ25 V / K at room temperature. The T 3/2 dependence observed in the S(T) curves for T ഛ 30 K is consistent with the electron-magnon scattering process. The high anisotropy and temperature dependence of the S(T) curves may be explained by adopting a phenomenological model for a Kondo lattice.

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