Magnetothermodynamics of Ce2Mg3(NO3)12· 24H2O. I. Heat capacity, entropy, magnetic moment from 0.5 to 4.2°K with fields to 90 kG along the a crystal axis. Heat capacity of Pyrex 7740 glass in fields to 90 kG

Abstract

The heat capacity of a 4.023 cm diam spherical single crystal of cerium magnesium nitrate hydrate has been measured with stabilized fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the a crystal axis, from 0.5 to 4.2°K. The zero of electronic entropy was reached at fields of 90, 65, and 40 kG and the lower temperatures. The isoerstedic entropy changes derived from heat capacity series were interconnected by 28 series of temperatures vs fields on isentropes. Analysis of the heat capacity data indicated that the first excited doublet is $\text{70.5± 1.0\hspace{0.17em}}\mathrm{cal}/{\mathrm{mole\; Ce}}^{\text{3+}}$ above the ground doublet. The splitting factor of the ground doublet was evaluated at $g_{\mathbf{H}}{\text{=1.838}}_5{\text{−5.20× 10}}^{\text{−12}}{\mathbf{H}}^2\text{± 0.001}$ . An applied magnetic field introduces an internal energy change of ${\text{1.39× 10}}^{\text{−15}}{\mathbf{H}}^3\hspace{0.17em}\mathrm{cal}/{\mathrm{mole\; Ce}}^{\text{3+}}$ (H in gauss) to the ground doublet enthalpy separation. The magnetic moment was measured over the same ranges of field and temperature as the heat capacity. Near 0.5°K, and over the range 40 to 90 kG, the total moment reaches definite limits at each field. Subtracting the limiting value of the temperature‐dependent moment, ${\text{5134−4.36× 10}}^{\text{−8}}{\mathbf{H}}^2\mathrm{G}·{\mathrm{cm}}^3/{\mathrm{mole\; Ce}}^{\text{3+}}$ , from the total, enabled the evaluation of the differential temperature‐independent magnetic susceptibility as, ${\chi }_{\mathrm{T\hspace{0.17em}}\mathrm{ind}}{\text{=2.221× 10}}^{\text{−2}}{\text{−1.71× 10}}^{\text{−13}}{\mathbf{H}}^2$ . Thus ${\mathbf{M}}_{\mathrm{limit}\text{T→ 0}}{\text{=5134+2.221× 10}}^{\text{−2}}\mathbf{H}{\text{−4.36× 10}}^{\text{−3}}{\mathbf{H}}^2{\text{−5.7× 10}}^{\text{−14}}{\mathbf{H}}^3$ , where H is in gauss. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5 to 4.2°K. The heat capacity of 7740 Pyrex glass has been measured over the same ranges.