Magnetic cooling, in which a magnetic field is used to change the temperature of a material, offers a profoundly different energy solution to applications involving power generation, heating, and refrigeration. Magnetic cooling is potentially an environmentally friendly, energy-efficient technology capable of outperforming conventional gas-compression refrigeration. It has been over fifteen years since the discovery of materials that can convert magnetism for cooling in normal operating conditions, but much is still unknown about how to optimize the manufacture and performance of these materials. This Designing Materials to Revolutionize and Engineer our Future (DMREF) project seeks to identify and optimize the chemical compositions of magnetic alloys, and understand the fundamental scientific properties that control this important behavior. A combined computational and experimental design approach will be used to identify the optimal candidate systems rapidly. Advanced computational methods will be used to predict and design alloys exhibiting the strongest effect; the most promising compositions discovered will then be synthesized and tested in the laboratory. The expected results are (i) the identification of several high-performance magnetic alloys for cooling and refrigeration, and (ii) an assessment of the performance attainable in this highly promising class of materials.
This program focuses on optimizing performance within one of the most promising class of materials: the metamagnetic Ni-Mn-Sn and Ni-Mn-In-(Co) shape memory alloys. Due to a unique coupling between two design degrees of freedom, magnetism and crystal structure, these Heusler-type alloys have the potential to dramatically change our approach to cooling and refrigeration. This effort brings a combined computational/experimental methodology to design and optimization, via quantum mechanical simulation methods and unique experimental capabilities to measure performance under large magnetic fields. A set of target performance metrics, elastic constants, phonon modes, spin wave stiffnesses, and exchange interaction energies - will be calculated using quantum mechanical models coupled with phenomenological descriptions. For the most promising candidates, targeted experiments on single crystal samples will be used to validate the computational models by studying the magnetic field induced transition from the martensite phase to the austenite phase in selected compositions producing a significant change in magnetization. Ultimately this program will provide an exhaustive assessment across a spectrum of candidates in the metamagnetic shape memory alloys Ni-Mn-Sn and Ni-Mn-In-(Co).
