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

A tiny adiabatic-demagnetization refrigerator (T-ADR) has been developed for a commercial superconducting quantum interference device magnetometer [Magnetic Property Measurement System (MPMS) from Quantum Design]. The whole T-ADR system is 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 is self-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) used as a magnetic refrigerant, the routinely achievable lowest temperature is $\sim 0.56$K\mathrm{.}Thelowerdetectionlimitforamagnetizationanomalyis$\sim 1 \times 10^{-7}$ 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 the magnetic refrigerant.