Magnetothermodynamics of Single-Crystal CuSO4·5H2O. IV. Properties over the Range 0.4°–4.2°K with Fields to 90 kG ‖ to the β Magnetic Axis

The heat capacity, magnetic moment, and entropy of CuSO₄·5H₂O have been measured in stabilized magnetic fields of 0, 1, 3, 5, 10, 20, 30, 50, 70, and 90 kG, over the range 0.4°–4.2°K. The field was directed along the $\beta$ magnetic axis of a 3.700‐cm‐diam spherical single crystal. The heat capacity measurements show that the nuclear spin polarization at 90 kG is in equilibrium with the lattice at temperatures down to 0.75°K. The data are uncorrected for the demagnetizing effect of the spherical sample. Temperature‐independent paramagnetism is much smaller than the diamagnetism as shown by a net temperature‐independent susceptibility of −1.0 × 10⁻⁴ cm³/mole. The gyromagnetic ratio, $g_{\beta }\text{\hspace{0.17em}=\hspace{0.17em}2.259}$ , may be compared with our previously determined values $g_{\alpha }\text{\hspace{0.17em}=\hspace{0.17em}2.081}$ and $g_{\gamma }\text{\hspace{0.17em}=\hspace{0.17em}2.269}$ . The electronic entropy was found to be $R$ ln 2 in agreement with previous work. Conditions during a temperature range in which equilibrium between the nuclear spin system and the lattice is lost are described.