Magnetothermodynamics of CuK2(SO4)2·6H2O. I. Heat Capacity, Entropy, Magnetic Moment, from 0.5 to 4.2°K with Fields to 90 kG along the b Crystallographic Axis

Abstract

The heat capacity and magnetic moment of a 3.912‐cm‐diam spherical single crystal of CuK₂(SO₄)₂·6H₂O have been measured over the range 0.5–4.2°K, with stabilized magnetic fields of 0, 0.5, 1.0, 2.5, 5, 10, 15, 25, 40, 65, and 90 kG directed along the $b$ crystallographic axis. No evidence of magnetic irreversibility was found. At the lower temperatures, magnetic saturation was attained at 90 and 65 kG. The temperature‐dependent saturation moment was found to be 6253 G·cm³/mole, corresponding to $g_b\text{\hspace{0.17em}=\hspace{0.17em}2.239}$ . The zero of entropy for the electronic and lattice systems was located by the essentially zero heat capacity near 1°K and 90 kG. Thirty‐eight temperature‐field isentropes were measured to correlate the entropies throughout the various isoerstedic heat capacity series. The upper limit of the electronic entropy was found to be 1.379 gibbs/mole compared to the expected $R\ln \text{2\hspace{0.17em}=\hspace{0.17em}1.377}\mathrm{gibbs}/\mathrm{mole}$ . The lattice heat capacity below 4°K is given by ${\text{C\hspace{0.17em}=\hspace{0.17em}3.66\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{T}^3\mathrm{gibbs}/\mathrm{mole}$ . Smoothed values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment, isothermal differential magnetic susceptibility, isoerstedic differential temperature coefficient of magnetic moment and its thermodynamic equivalent, the isothermal differential change of entropy with field, and the isothermal work of magnetization have been tabulated.