Magnetothermodynamics of α-MnCl2·4H2O. III. Heat Capacity, Entropy, Magnetic Moment, from 0.3 to 4.2°K with Fields to 90 kG along the [100] Crystal Axis

Abstract

The heat capacity and magnetic moment of a 3.934 cm diameter spherical single crystal of α‐MnCl2·4H2O have been measured with stabilized solenoid fields of 0, 1, 5, 10, 14, 22, 25, 40, 65, and 90 kG, along the [100] crystal axis. The magnetic saturation value, 27 999 G·cm3 mole−1, obtained at both 65 and 90 kG, and 0.46°K, indicates that the temperature independent susceptibility is zero and the saturation moment of the temperature‐dependent system is 27 999 G·cm3 mole−1, equivalent to g [100] = 2.005 . At 90 kG the nuclear spins contributed a heat capacity term of 5.6 × 10 −3 T −2 gibbs mole −1 . The amount of enthalpy required to remove quanta of angular momentum from the saturated condition at 90 kG was found to be 20.2 cal mole−1. This is less than gβ H = 24.09 cal mole −1 , the magnetic work, by 3.9 cal mole−1. This difference is the amount of stored internal energy contributed by the saturated condition to this limiting process, and is consistent with antiferromagnetic interactions. Extrapolation of the magnetic moment–temperature curves to the absolute zero yields the expression M = 0.9946H + 2.50 × 10−6 H 2G·cm3 mole−1 at 0°K. On this slightly curved line the saturation value, 27 999 G·cm3 mole−1, is reached at 26 400 G, and the work of magnetization to saturation, ∫ H dM , is 9.02 cal mole−1. Temperature field observations on 26 isentropes were used to correlate the entropies along 10 isoerstedic heat capacity series. The zero of electronic and lattice entropy was located from the low temperature heat capacities at 90 kG. The upper limit of the electronic entropy was found to be 3.561 gibbs mole−1 in complete agreement with the Rln6 expected for an S = 5 2 state. Smoothed correlated values of the heat capacity,entropy,enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, and the work of magnetization have been tabulated.