Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point

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 ∂ S /∂ B near a B -induced QCP via absolute measurements of the magnetocaloric effect (MCE), (∂ T /∂ B ) 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 Cu 2+ -containing coordination polymer, which is a very good realization of a spin-½ antiferromagnetic Heisenberg chain—one of the simplest quantum-critical systems.