Thermodynamic Temperature and Heat Capacity of NiSiF6·6H2O without Heat Introduction below 0.35°K. Magnetic Moment and Internal Energy from 0.05° to 4.2°K. Fields 0–90 kG Perpendicular to the c Axis

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Abstract
Values of the magnetic moment of a 3.5‐cm‐diam spherical single crystal of NiSiF6·6H2O have been determined over the range 0.3°—4.2°K and 0–90 kG. The field was perpendicular to the c crystallographic axis. The differential isothermal magnetic susceptibility and the isothermal work of magnetization are given. The data have been combined with our previous related measurements of heat capacity and entropy to evaluate the changes in internal energy and enthalpy. All of the data apply to a spherical crystal without correction for the demagnetizing effect. The temperature‐independent magnetic moment was estimated as 3.4×10−4H G·cc/mole from the high‐field observations. Using this value to correct the data, ga,b=2.233, and a similar correction of our previous data with H ∥ c axis gives gc=2.241 for the temperature‐dependent moment. Measurements of magnetic moment as a function of field on 40 adiabatics have been used to extend the thermodynamic temperature and heat capacity below the region of heat introduction, thus avoiding problems of thermal contact and thermal conductivity at very low temperatures.