title: High-resolution thermal expansion measurements under helium-gas pressure.
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 ≤ T ≤ 300 K and hydrostatic pressure P ≤ 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 ~/= 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.
authors.affiliation: Physics Institute, Goethe University Frankfurt(M), SFB/TR49, D-60438 Frankfurt(M), Germany. Manna@physik.uni-frankfurt.de
authors.forename: Rudra Sekhar
authors.initials: RS
authors.lastname: Manna
authors.forename: Bernd
authors.initials: B
authors.lastname: Wolf
authors.forename: Mariano
authors.initials: M
authors.lastname: de Souza
authors.forename: Michael
authors.initials: M
authors.lastname: Lang