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 ∼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.

• Received 16 May 2001

DOI:https://doi.org/10.1103/PhysRevB.64.235103