Magnetic cooling is potentially an environmentally friendly, energy-efficient technology capable of outperforming conventional gas-compression refrigeration. 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.