Tiny adiabatic-demagnetization refrigerator for a commercial superconducting quantum interference device magnetometer

摘要

A tiny adiabatic-demagnetization refrigerator (T-ADR) has been developed fora commercial superconducting quantum interference device magnetometer [MagneticProperty Measurement System (MPMS) from Quantum Design]. The whole T-ADR systemis fit in a cylindrical space of the diameter $8.5$ mm and the length $250$ mm,and can be inserted into the narrow sample tube of MPMS. A sorption pump isself-contained in T-ADR, and hence no complex gas handling system is necessary.With the single crystalline Gd$_3$Ga$_5$O$_{12}$ garnet ($\sim 2$ grams) usedas a magnetic refrigerant, the routinely achievable lowest temperature is $\sim0.56$ K. The lower detection limit for a magnetization anomaly is $\sim 1\times 10^{-7}$ emu, estimated from fluctuation of the measured magnetization.The background level is $\sim 5 \times 10^{-5}$ emu below 2 K at $H = 100$ Oe,which is largely attributable to a contaminating paramagnetic signal from themagnetic refrigerant.