Electrical resistivity, electronic heat capacity, and electronic structure ofGd5Ge4

Abstract

Temperature and dc magnetic-field dependencies of the electrical resistivity (4.3--300 K, 0--40 kOe) and heat capacity (3.5--14 K, 0--100 kOe) of polycrystalline ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ have been measured. The electrical resistivity of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ shows a transition between the low-temperature metallic and high-temperature insulatorlike states at \ensuremath{\sim}130 K. In the low-temperature metallic state both the resistivity and electronic heat capacity of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ indicate a possible presence of a narrow conduction band. Both low- and high-temperature behaviors of the electrical resistivity of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ correlate with the crystallographic and magnetic phase transitions induced by temperature and/or magnetic field. Several models, which can describe the unusual behavior of the electrical resistance of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ above 130 K, are discussed. Preliminary tight-binding linear muffin-tin orbital calculations show that ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ behaves as a metal in the low-temperature magnetically ordered state, and as a Mott-Hubbard ``semiconductor'' in the high-temperature magnetically disordered state.