Refrigeration in Adiabatically Confined Anisotropic Transition Metal Complexes Induced by Sudden Magnetic Field Quenching

The article is devoted to the theoretical development of the mechanisms of molecular refrigeration, the area combining molecular magnetism and material science with promise for low-temperature physics and quantum computing, where conventional principles of refrigeration become inefficient. Given this general trend, we propose the concept of the magnetothermal effect in magnetically anisotropic complexes of 3d metal ions, caused by fast magnetic field quenching. Within this concept, the most topical case of an axially magnetically anisotropic system isolated from the environment by adiabatic envelope is analyzed. We evaluate the temperature change as a function of the initial temperature and magnetic field and also its dependence on the sign and the magnitude of the axial zero-field splitting parameter and the Debye temperature. Correlations are revealed between the sign of the magnetic anisotropy (dictated by the sign of the axial zero field splitting parameter) and the sign of the thermal effect (heating versus cooling) caused by field quenching. The temperature change is shown to be negative (cooling) in the case of complexes exhibiting easy-axis-type magnetic anisotropy, while for the case of easy-plane-type anisotropy, it proves to be positive (heating). The thermal effects are shown to have an efficient control by varying the initially applied field. These findings allow us to propose complexes exhibiting easy-axis-type magnetic anisotropy as candidates for achieving a low-temperature refrigeration effect caused by fast field quenching and also to employ the established magnetothermal correlations to the analysis of magnetic anisotropy.