Magnetothermodynamics of Antiferromagnetic, Ferroelectric β-Gd2(MoO4)3. I. Heat Capacity, Entropy, Magnetic Moment of the Electrically Polarized Form from 0.4 to 4.2°K with Fields to 90 kG along the c Crystal Axis

Abstract

The magnetic moment of a 2.49‐cm diam spherical single crystal of electrically polarized β‐Gd₂(MoO₄)₃ has been measured at stabilized fields of 500, 1000, 1500, 2000, 2200, 2300, 2500, 3500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the c crystal axis and over the range 0.3–4.2°K. The heat capacity has been measured at fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G over a similar temperature range. The temperature dependent magnetic moment reached saturation at the higher fields and low temperatures. As expected, any effect of reversing the magnetic field with respect to the electrical polarization was too small to be detected, i.e., less than 0.01% of the magnetic moment. The general character of the magnetic moment and its temperature derivatives vs field at 0.5°K and below indicates the development of an antiferromagnetic system. The fact that the heat of vaporization of momentum (h/2π) from the essentially saturated state exceeds 2M_satH/7, both at 90 and 65 kG, indicates that the energy of the $\text{j = ± 5/2}$ pair is above $\text{j = ± 7/2}$ in zero field. Temperature‐field observations on 31 isentropes were used to correlate the entropies along 10 isoerstedic heat capacity series. The entropy zero of the electronic and lattice systems was located at magnetic saturation by means of the heat capacity series at 90 and 65 kG. 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 0.4–4.2°K.