We have improved the top-loading type dilution refrigerator and Ag-based calorimetry cell. A top-loading type dilution refrigerator is very useful to perform several thermal measurements at extremely low temperature region due to the easiness of its operation and preparation. We have used Ag-based calorimety cell, which is available at low temperature region and has the compatibility for top-loading type dilution insert and large-scale dilution refrigerator at IMS. We have confirmed that it can be used for heat capacity measurements by thermal relaxation method from 100 mK to 1 K. A measurement of the cell was performed using high resolution ac-resistance bridge (LakeShore 370 and Linear Research LR-700) with low excitation voltages smaller than 2 mV. We have also attached extra wires to prohibit small vibration of the sample stage. The base line of the heating curve has been stabilized with in ±2 mK at 100 mK and succeeded in accurate measurement of the sample stage of which heat capacity is 8 nJ/K at 200mK. The extended usage of this calorimetry cell from extremely low-temperature up to 12 K is expected in future.
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Fig. 1. Top-loading type dilution refrigerator insert. The system is available in φ30 mm sample space of VTI. The adiabatic can is sealed by wood alloy. |
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Fig 2. Heat capacities measured with top-loading type dilution refrigerator insert and large-scale dilution refrigerator (previous work). |