Development of ³He insert for Magnetization Measurements down to T =0.4 K with SQUID magnetometer

We have developed a 9-mm-diameter ³He insert for precise magnetization measurements down to T =0.4 K that is attachable to a commercial superconducting quantum interference device magnetometer. The insert is made from a thin-walled stainless steel pipe with an inner diameter of 6.2 mm, which determines the maximum sample size. ³He gas is condensed in the pipe, which is liquefied by ⁴He gas at T =1.8 K generated by the magnetometer via the heat exchanger of a Cu vacuum jacket with an outer diameter of 8.6mm soldered to the stainless steel pipe. The temperature of the insert is decreased to T 0=.5 K by evacuating liquid ³He using a rotary pump and then to T -0.36 K with a sorption pump. From the diamagnetization signal of a superconducting Al chip with a mass below 0.1 mg, the magnetization resolution with the insert is confirmed to be less than 10^-7 emu. We measure the temperature dependence of magnetization down to T =0.5 K in Pr_xLa_1-xPb₃, which is a good candidate for the reality of the quadrupolar Kondo effect, using the ³He insert. Non-Fermi liquid behavior of the nonlinear susceptibility in χ₃ with a -lnT dependence is detected in the [100] and [110] directions below T =2.5 K, suggesting the screening of quadrupolar moments. In contrast, χ₃ in the [111] direction becomes constant below T =3 K. The observed features indicate that a low-lying Γ₃ doublet plays a crucial role in the anomalous properties of Pr_xLa_1-xPb₃.