Entropy changes and caloric effects driven by charge transfer: Application to YbInCu₄

In this work, we propose a new physical mechanism based on charge transfer to produce large entropy and caloric effects even in non magnetic solid materials. In order to carry out the calculations, we use a two subband model in which a strongly correlated narrow band is coupled with a wide conduction electrons band. In the model, the charge transfer is controlled by the energy bandwidth and the hybridization parameter. The entropy and the caloric functions are calculated using the standard relations [1].
We apply the model to YbInCu₄ which exhibits an itinerant behavior at low temperature and a local magnetic moment profile at temperatures larger than the valence temperature T_V around 42 K [2]. Our theoretical results, show that YbInCu₄ presents a large entropy change around 42 K due to the charge transfer from the 4f band to the electron sea. Besides, the isothermal entropy change upon pressure variation exhibits sizeable values in a wide temperature range. This outstanding result, which needs experimental data to be confirmed, can be very important for solid state refrigerators tecnology.

[1] N. A. de Oliveira, P. J. von Ranke, Physics reports, 489, 89 (2010).
[2] J. L. Sarrao, Physica B 259-261 128, (1999)