Development of 3 He 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 PrxLa1-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 PrxLa1-xPb3.