Magnetothermodynamics ofagr;hyphen;MnCl2middot;4H2O. II. Heat Capacity, Entropy, Magnetic Moment, from 0.4 to 4.2deg;K with Fields to 90 kG along thebCrystallographic Axis

摘要

This work is a continuation of our previous magnetothermodynamic measurements on a 3.934hyphen;cmhyphen;diam spherical single crystal of MnCl2middot;4H2O in which case the field was directed along theccrystallographic axis. Here the heat capacity and magnetic moment have been measured between 0.3deg; and 4.2deg;K with stabilized solenoid fields of 0, 1, 5, 7.5, 10, 14, 18, 22, 25, 40, 65, and 90 kG, along thebcrystallographic axis. At 0.716deg;K and fields of 90, 80, and 70 kG. the electron system was magnetically saturated. The derived temperaturehyphen;independent magnetic susceptibility was found to be minus;thinsp;1.6thinsp;times;thinsp;10minus;4cm3moleminus;1and the saturation moment of the temperaturehyphen;dependent system is 27 974 Gmiddot;cm3moleminus;1, equivalent togbthinsp;equals;thinsp;2.004. At 90 kG the nuclear spins were found to contribute a heat capacity term oflpar;5.9thinsp;times;thinsp;10minus;3thinsp;sol;thinsp;T2rpar;gibbs moleminus;1. The amount of enthalpy required to remove quanta of angular momentum from the saturated condition at 90 kG was found to be 20.63 cal moleminus;1of angular momentum. This is less thangbgr;Hthinsp;equals;thinsp;24.07cal moleminus;1, the magnetic work, by 3.44 cal moleminus;1, which is the amount of stored internal energy contributed to the saturated condition for this limiting process, and indicates antiferromagnetic interactions. Extrapolation of the magnetic momentndash;temperature curves to absolute zero yields the expression Mthinsp;equals;thinsp;1.056Hthinsp;plus;thinsp;9.0thinsp;times;thinsp;10minus;7H2Gmiddot;cm3moleminus;1at 0deg;K. On this slightly curved line the saturation value, 27 974 Gmiddot;cm3moleminus;1, is reached at a field of 25 920 G, and the work of magnetization,0HHdM,equals 8.73 cal moleminus;1at 0deg;K. Temperaturendash;field observations on 31 isentropes were used to correlate the entropies along 12 isohyphen;Oerstedic heat capacity series. The zero of electronic and lattice entropy was located from the lowhyphen;temperature values of the heat capacity series at 90 kG. The upper limit of the electronic entropy was found to be 3.559 gibbs moleminus;1, compared toRln6thinsp;equals;thinsp;3.561gibbs moleminus;1. Smoothed, correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment, isohyphen;Oerstedic temperature coefficient of the magnetic moment (which equals the isothermal derivative of entropy with respect to field), and the magnetic work have been tabulated.