The presence of a quantum critical point (QCP) can significantly affect the thermodynamic properties of a material at finite temperatures T. This is reflected, e.g., in the entropy landscape S(T, r) in the vicinity of a QCP, yielding particularly strong variations for varying the tuning parameter r such as pressure or magnetic field B. Here we report on the determination of the critical enhancement of δS/δB near a B-induced QCP via absolute measurements of the magnetocaloric effect (MCE), (δT/δB)S, and demonstrate that the accumulation of entropy around the QCP can be used for efficient low-temperature magnetic cooling. Our proof of principle is based on measurements and theoretical calculations of the MCE and the cooling performance for a Cu2+-containing coordination polymer, which is a very good realization of a spin-1/2 antiferromagnetic Heisenberg chain - one of the simplest quantum-critical systems.
@article{arxiv.1012.3328,
title = {Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point},
author = {B. Wolf and Y. Tsui and D. Jaiswal-Nagar and U. Tutsch and A. Honecker and K. Removic-Langer and G. Hofmann and A. Prokofiev and W. Assmus and G. Donath and M. Lang},
journal= {arXiv preprint arXiv:1012.3328},
year = {2015}
}