Magnetic cooling by the application of external pressure in rare-earth compounds

A method for cooling by the application of pressure was recently proposed. As in any other (magnetic) adiabatic cooling technique, the cooling results from a change in the magnetic entropy of the system under investigation. As opposed to the well known method of adiabatic demagnetization (for paramagnets) or to the magnetocaloric effect (for ferromagnets and antiferromagnets), the entropy change does not result from the application of an external magnetic field, but from the application of external pressure (barocaloric effect). The pressure-induced change in the magnetic entropy may be obtained by different mechanisms including pressure-induced structural or/and magnetic phase transitions, pressure-induced changes in the degree of $4f$-conduction electron hybridization in Kondo systems, pressure-induced valence transitions, and pressure-induced spin fluctuations. The present work illustrates this new concept of adiabatic cooling on the basis of recent experimental data. The data are discussed within a simple model balancing the total entropy as a function of microscopic thermodynamic parameters of the system under investigation. Implications for a possible technical use of this effect are addressed.