Towards a Design Framework for Magnetocaloric Shape Memory Alloys

The use of the magnetocaloric effect is a potentially environmentally green, energy-efficient, solid-state technology capable of outperforming conventional gas-compression refrigeration. The discovery of the near-room-temperature giant magnetocaloric effect over fifteen years ago expanded the scope of magnetic cooling from cryogenic to standard room temperature refrigeration. In the giant magnetocaloric effect, the application or removal of a magnetic field induces a structural phase transformation, and the latent heat of the phase transition induces a temperature change in the material (adiabatic demagnetization). We will discuss our recent progress on the development of a framework for the design, discovery, and optimization of Heusler shape memory alloys exhibitting enhanced magnetocaloric performance. To optimize the effect, the entropy change of the phase transition must be as large as possible. We have developed a framework that couples first-principles calculations of underlying magnetic exchange interactions together with a modified statistical mechanics Blume-Emery-Griffiths models to obtain the thermodynamic properties of the magnetic Heusler shape memory alloys scanning across different compositions. We have validated our approach on the Ni₂Mn_1+xIn_1-x and Ni₂Fe_1+xGa_1-x family, and now are extending it to as-of-yet unknown material compositions.