Magnetic ordering in the pressure-stabilized high-temperature phase of YbInCu₄

To elucidate the ground state of the pressure-stabilized high-temperature (HT) phase of YbInCu₄, we have carried out electrical resistivity ρ and ac-susceptibility χ_ac measurements at high pressures. For pressures above 2.49 GPa, the first-order valence transition is completely suppressed (below 80 mK). Separately, above 2.39 GPa, a clear peak appears in χ_ac with a small kink in ρ at around T_M = 2.4 K. The χ_ac peak is easily diminished by applying low magnetic fields and disappears above 500 Oe. The characteristic behavior of χ_ac at T_M can generally be ascribed to the onset of long-range ferromagnetic ordering and, therefore, the ground state of the pressure-stabilized HT phase is most probably a ferromagnetically ordered state. This result is compatible with the occurrence of weak ferromagnetism recently reported for the Y-substituted compound Yb_0.8Y_0.2InCu₄ under pressure of 1.2 GPa.