Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. III. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K with fields to 90 kG along the a crystal axis

Abstract

The heat capacity of a 3.930 cm diam spherical single crystal of neodymium ethyl sulfate 9 hydrate (NES) 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. This axis is in the isotropic ab plane which is perpendicular to the c axis. The temperature range was from 0.5 to 4.2 °K. After small adjustments were applied for the nuclear polarization of the protons, plus 143Nd (12.20%) and 145Nd (8.30%) isotopes, an effective zero of electronic and lattice entropy was found at 1.25 °K and 90 000 G. These isoerstedic entropy changes derived from the heat capacity series were interconnected by 43 series of adiabatics corrected to isentropes. The heat capacity in zero magnetic field was found to be CH=0=2.27×10−3/T2 −8.45×10−5/T3+1.13×10−3T3+2.15×10−5T5 gibbs/FW below 4 °K, where the first two terms are due to the hyperfine states of 143Nd and 145Nd. The magnetic moment was measured by the potentiometric method at the above fields and temperature ranges used for heat capacities. The saturation limit of the temperature-dependent moment was 5694 G⋅cm3/FW, corresponding to ga=g⊥=2.039. The temperature-independent magnetic susceptibility, χa=0.00576 cm3/mole NES. These values may be compared with our previously measured gc=g∥ =3.594 and χc=0.00341 cm3/mole NES. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment, and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5–4.2 °K. These data will be used as starting references for investigating the properties of NES in the region below 0.5 °K, with the assistance of calorimetric heat introduction. Comparison of the magnetic moment and heat capacity data with an ionic crystal field model, with a dipolar molecular field, using parameters derived from the measured data, gives general good agreement.