The electrical resistivity ρ and thermopower S of the cubic Laves phase compounds Ho(Co1-xAlx)2 (x = 0, 0.15 and 0.20) have been measured at temperatures from 2 K to 300 K in magnetic fields up to 10 T. The measurements of ρ under pressures up to 3 GPa have been performed in the temperature range between 2 K and 300 K. Both ρ(T) and S(T) of the pure HoCo2 reveal abrupt changes at the magnetic ordering temperature TC, indicating the first order transition. ρ(T) of the Al substituted samples (x = 0.15 and 0.20) show anomalous behavior in the form of an increase below TC. The variations of ρ and S at TC clearly indicate that the type of the magnetic transition changes under substitution of Al for Co from the first order to the second order. The residual resistivity of Ho(Co1-xAlx)2 shows a rapid increase with increasing x. TC increases linearly for x < 0.15, having a maximum at x ≈ 0.15 and decreases with further increase of x. The peculiar x dependence of TC and the anomalous behavior of ρ(T) and S (T) around TC are related to the metamagnetic instability of Co 3d subsystem and to fluctuating local magnetic susceptibility due to the atomic substitution.
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