Capacitance measurement of magnetic specific heat

A new technique–low frequency capacitance (C) measurement–has been used to study the critical behavior of both isotropic and anisotropic antiferromagnets. We find that dC/dT is accurately proportional to the known magnetic specific heat Cm of FeF2. This indicates that both dε/dT and dl/dT scale with Cm. For cubic KNiF3, the critical exponent (Cm=At−α) has been found to be α=−0.151±.004 and A/A′=1.56±0.03. The experiments measured the capacitance of disk-shaped samples with a three-terminal capacitance technique. A ratio transformer bridge was employed, yielding a resolution in ΔC/C of about 10−8. The quality of the results is comparable to the best obtainable from conventional Cm and birefringence measurements.