Magnetic and transport properties of Yb 5T 4Ge 10 (T=Co, Rh, Ir)

Abstract

The magnetic and transport properties of Yb 5T 4Ge 10 and Lu 5T 4Ge 10 (T=Co, Rh, Ir) have been investigated. All Yb compounds are metals with the paramagnetic state above 1.2 K. Some magnetic transition is commonly expected below 1.2 K from the result of the specific heat. Single crystal of Yb 5Rh 4Ge 10 has been grown by the Bridgman method. Magnetic susceptibility of Yb 5Rh 4Ge 10 shows a strong anisotropy with the easy-plane type within the c-plane. At 2 K, magnetization of Yb 5Rh 4Ge 10 for H∥ a gradually increases as increasing the magnetic field and saturates to a constant value of 4.5 μ B/f.u. in H = 5 0 kOe in contrast to magnetization for H∥ c, which keeps increasing to 0.9 μ B/f.u. in H = 5 0 kOe . The magnetic part of the specific heat for Yb 5Rh 4Ge 10 shows the Schottky anomaly centered at about 60 K due to the CEF effect, which acts on the eight-hold multiplet of Yb 3+ ion. Furthermore, a broad peak appears at low temperatures by the application of the magnetic field. Height of this peak is very low as compared to the Schottky peak expected for the two-levels split from the ground state doublet for five Yb 3+ ions in formula unit. The magnetic entropy gain in the magnetic field for Yb 5Rh 4Ge 10 at 300 K does not attain to 5 R ln8, therefore, there is a possibility that the mixed valence state consisted of three or four Yb 3+ ions among five Yb ions in formula unit is realized in all temperature range. A similar situation is found in Yb 5Co 4Ge 10 and Yb 5Ir 4Ge 10.