Heat Capacity in Magnetic and Electric Fields Near the Ferroelectric Transition in Tri-Glycine Sulfate

TL;DR

This study investigates the specific heat behavior of tri-glycine sulfate near its ferroelectric transition under magnetic and electric fields, revealing how external fields and surface conditions influence the transition's nature and critical exponents.

Contribution

It demonstrates the impact of external magnetic and electric fields, as well as surface grounding, on the specific-heat anomaly and critical behavior near the ferroelectric transition.

Findings

External fields sharpen the specific-heat anomaly to a lambda shape.

Surface short-circuiting reveals intrinsic transition behavior.

Critical exponents were determined from the lambda-shaped anomaly.

Abstract

Specific-heat measurements are reported near the Curie temperature ($T_C$~= 320 K) on tri-glycine sulfate. Measurements were made on crystals whose surfaces were either non-grounded or short-circuited, and were carried out in magnetic fields up to 9 T and electric fields up to 220 V/cm. In non-grounded crystals we find that the shape of the specific-heat anomaly near $T_C$ is thermally broadened. However, the anomaly changes to the characteristic sharp $\lambda$-shape expected for a continuous transition with the application of either a magnetic field or an electric field. In crystals whose surfaces were short-circuited with gold, the characteristic $\lambda$-shape appeared in the absence of an external field. This effect enabled a determination of the critical exponents above and below $T_C$, and may be understood on the basis that the surface charge originating from the pyroelectric coefficient, $dP/dT$, behaves as if shorted by external magnetic or electric fields.