Successive Magnetic Transitions in a Frustrated Compound YbAgGe

Abstract

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 0.6 J/mol K released at T_M1 is attributed to the combination of the Kondo effect and magnetic frustration effect. When the magnetic field B||a is increased to 5 T, T_M1 is depressed to 0 K. At this critical magnetic field, the magnetic susceptibility χ follows the Curie–Weiss law, χ⁻¹−χ₀⁻¹∝T, in a wide temperature range from 0.45 K to 300 K.