Magnetothermodynamics of gadolinium gallium garnet. I. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K, with fields to 90 kG along the [100] axis

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Abstract
The magnetic moment of a 2.44 cm diam spherical single crystal of gadolinium gallium garnet has been measured with stabilized fields of 500, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the [100] axis, over the range 0.35 to 4.2 °K. The heat capacity was measured over similar ranges, except that 500 G was omitted and zero field included. The magnetic moment reached saturation at 0.35 °K and 90 000 G. The electronic and nuclear spin components of the heat capacity at 90 000 G could be separated from each other near 1 °K, thus locating a zero of entropy for the electronic system. By means of 34 adiabatics, corrected to isentropes, which crossed most of the isoerstedic heat capacity series, the entropies as a function of field and temperature were evaluated in terms of the zero reference. The sample has (0.4 ± 0.1) mole% excess entropy over the maximum R ln 8 for Gd3+ ion. Thus the sample must have contained 0.4 mole% excess Gd over the stoichiometric amount for Gd3Ga5O12. Using the correction factor 0.9960, the saturation value for Gd3Ga5O12 is found to be 39 095 G · cm3/mole Gd3+. This corresponds to a g = 2.000 ± 0.002. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment, and its differential isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the ranges 0–90 kG and 0.5–4.2 °K.

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