Successive magnetic transitions in a frustrated compound YbAgGe

Low-temperature properties of a heavy fermion compound YbAgGe have been investigated by electrical resistivity, specific heat and magnetization measurements on a single crystalline sample. This compound, crystallizing in the hexagonal ZrNiAl-type Structure, undergoes two magnetic phase transitions at T-M1 = 0.8 K (second order) and T-M2 = 0.65 K (first order). Below T-M2, the jump of the resistivity along the a axis indicates gap formation on the Fermi Surface along the a axis. The extremely small magnetic entropy of 0.6J/mol K released at T-M1 is attributed to the combination of the Kondo effect and magnetic frustration effect. When the magnetic field B parallel to a is increased to 5 T, T-M1 is depressed to 0 K. At this critical magnetic field, the magnetic susceptibility chi follows the Curie-Weiss law. chi(-1) - chi(0)(-1) proportional to T. in a wide temperature range from 0.45 K to 300 K.