Development Of He-3 Insert For Magnetization Measurements Down To T=0.4 K With Squid Magnetometer

We have developed a 9-mm-diameter He-3 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. He-3 gas is condensed in the pipe, which is liquefied by He-4 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 He-3 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 He-3 insert. Non-Fermi liquid behavior of the nonlinear susceptibility in chi(3) 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, chi(3) in the [111] direction becomes constant below T = 3 K. The observed features indicate that a low-lying Gamma(3) doublet plays a crucial role in the anomalous properties of PrxLa1-xPb3.