Field‐induced quantum criticality – application to magnetic cooling

Abstract

Abstract Materials close to a quantum‐critical point – a zero‐temperature phase transition – exhibit anomalous thermodynamic properties also at finite temperatures. Close to a magnetic field‐induced quantum‐critical point, for example, the finite‐temperature entropy S T shows strong variations upon varying the magnetic field. Here we discuss the possibility to use this accumulation of entropy around a field‐induced quantum‐critical point for realizing an efficient magnetic cooling. Our proof‐of‐principle demonstration is based on measurements and theoretical calculations of the magnetocaloric properties of low‐dimensional spin‐1/2 antiferromagnets close to their field‐induced quantum‐critical points. We present results of the magnetocaloric effect Γ B = T −1 (∂ T /∂ B ) S ≈ const as a function of both field and temperature in the vicinity of the quantum‐critical point and discuss various performance characteristics, such as range of operation, efficiency and hold time. These figures are compared with those of a state‐of‐the‐art paramagnetic coolant.