Abnormal specific heat at low temperatures and transport properties in Mg-Cu-Ag-Gd bulk metallic glass

Abstract

We report the pronounced low-temperature specific-heat Cp anomalies in the Mg59.5Cu22.9Ag6.6Gd11 bulk metallic glass (BMG). The extrapolated electron's temperature coefficient γ0K is up to 681.8 mJ/(mol-Gd⋅Κ2) at 0 K, which is a heavy-fermion-like behavior. The low temperature specific heat indicates an enhancement of the conduction-electron effective mass m∗ below 7.5 K, suggesting that the Mg59.5Cu22.9Ag6.6Gd11 BMG is not free-electron-like solid. The excess specific heat in the Mg-based BMG is interpreted with tunneling states and spin glass state (magnetism) which are determined by subtracting electrons' and phonons' contribution to the specific heat below 12 K. The Boson peak (BP) temperature is located at 27 K, which is much higher than the reported values of other BMGs. And, a BP height of 0.047 mJ/(mol·K4) is obtained due to reduced free volume during copper mold casting with a slow cooling rate. The electrical resistivity was also investigated between 2 and 300 K, which has a negative temperature coefficient of resistivity (TCR) below 35 K (Kondo temperature, TK) and a positive value of 3.9 × 10−4/K above 35 K. There is a minimum at about 35 K for the electrical resistivity, which can be explained by the Kondo effect. For the resistivity above 35 K, it can be explained by the Faber-Ziman model due to the T-dependence change of structure factor.