High-resolution thermal expansion measurements under Helium-gas pressure

TL;DR

This paper presents a high-resolution capacitive dilatometer for measuring thermal expansion under helium-gas pressure, demonstrating its performance through experiments on azurite and revealing pressure effects on magnetic interactions.

Contribution

The paper introduces a novel high-resolution dilatometer capable of precise thermal expansion measurements under hydrostatic helium-gas pressure, with demonstrated application to magnetic materials.

Findings

Pressure significantly influences magnetic interactions in azurite.

The dilatometer achieves high resolution under varying pressures.

Measurements confirm the effectiveness of helium as a pressure medium.

Abstract

We report on the realization of a capacitive dilatometer, designed for high-resolution measurements of length changes of a material for temperatures 1.4 K $\leq T \leq$ 300 K and hydrostatic pressure $P \leq$ 250 MPa. Helium ($^4$He) is used as a pressure-transmitting medium, ensuring hydrostatic-pressure conditions. Special emphasis has been given to guarantee, to a good approximation, constant-pressure conditions during temperature sweeps. The performance of the dilatometer is demonstrated by measurements of the coefficient of thermal expansion at pressures $P \simeq$ 0.1 MPa (ambient pressure) and 104 MPa on a single crystal of azurite, Cu$_3$(CO$_3$)$_2$(OH)$_2$, a quasi-one-dimensional spin S = 1/2 Heisenberg antiferromagnet. The results indicate a strong effect of pressure on the magnetic interactions in this system.