Glassy Ferromagnetic Shape Memory Alloys: Interplay Between Disorder, Phase Transitions, and Multi-Physics Couplings
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NON-TECHNICAL SUMMARY: Shape Memory Alloys (SMAs) are a special type of crystalline metals that can recover their deformed shape upon heating, as a result of the reversible solid to solid structural phase transformations, i.e. martensitic transformations. Few recently discovered SMAs are also magnetic, and demonstrate simultaneous martensitic and magnetic transitions. The principal investigators have recently shown that careful manipulation of defects in these alloys can bring about novel glass-like behavior in which the ''amorphous'' structure is defined in terms of magnetic spin and/or strain. Such multi-functional coupling, the appearance of various types of solid states, and the resulting properties may provide completely new functionalities such as magnetic actuation, efficient magnetic refrigeration, thermal management, harvesting of waste mechanical energy, and cell growth stimulation via remotely actuated active tissue scaffolds. This award supports fundamental experimental and theoretical research and education to understand how different types of solid to solid phase transformations, glassiness, and crystal defects interact in magnetic SMAs and influence their functional properties. The new understanding is expected to positively impact future design and development of multifunctional smart materials. The award supports the training of undergraduate and graduate students in state-of-the-art experimental and computational materials techniques. An integral aspect of this project is the open dissemination of research results through a Materials Data Repository based on the National Institute of Standards and Technology''s Materials Data Curation System. TECHNICAL SUMMARY: NiMnIn-based Magnetic Shape Memory Alloys (MSMAs) exhibit a wide range of complex phenomena resulting from the interplay between configurational disorder and different types of phase transitions (ordering, magnetic, structural) including spin glass and strain glass transitions. These phase transitions result in multiple coupling modes involving thermal, magnetic and mechanical thermodynamic conjugate pairs. In turn, the alloys demonstrate rich responses that result in unique behavior such as magnetic exchange bias, tailorable thermal expansion, giant magneto-caloric and elasto-caloric effects. The principal investigators have shown that the degree of order and the presence of point defects and anti-phase boundaries play a fundamental role in controlling the stability of multiple competing phases but much remains unknown regarding the specific effect of configurational disorder on the magneto-thermo-mechanical properties of MSMAs. The goal of the combined computational-experimental approach in this project is to elucidate the mechanisms and microstructural features that determine the stability of the different competing phases, the onset of the phase transitions and their couplings. The focus is to use state-of-the-art multi-physics characterization and modeling to investigate the nature of magneto-thermo-mechanical couplings in NiMnIn MSMAs as a function of configurational order and various external stimuli (temperature, stress, and magnetic field or their combinations). In-situ investigation of micro and magneto structure coupled with neutron diffraction measurements in combination with first-principles calculations and Monte Carlo simulations are used to examine the effect of configurational disorder on the magneto-structural phase transitions and the onset of glassy behavior. The major scientific impact of this project is expected to be the development of sound, multi-physics-based alloying and heat treatment guidelines for tuning magnetic and structural responses in magnetic SMAs.