Novel Physical Behaviors Driven by Magnetostructural Phase Transitions

Shane Stadler, Louisiana State University (PI)

Naushad Ali (PI) and Saikat Talapatra (Co-I), Southern Illinois University

Novel and useful physical behaviors occur in materials that undergo transitions in which there is a simultaneous transformation in crystalline structure and magnetic state. Such a transformation is called a magnetostructural transition, and can be driven by magnetic field, temperature, strain, or pressure. These transitions can result in dramatic changes in material properties including magnetic configuration, electronic state, crystal structure and cell volume, transport properties, and electronic structure, and often lead to novel physical behaviors such as giant magnetoresistance, asymmetric magnetoresistive switching, ferromagnetic shape-memory effects, anomalous Hall effects, and bulk exchange bias. In this project, we are primarily interested magnetostructural transitions driven by magnetic field or hydrostatic pressure that generate a change in temperature of the material. Such solid-state caloric materials have applications in solid-state cooling, the burgeoning field that is driving promising new refrigeration technologies which are predicted to be more energy efficient and environmentally friendly than their conventional, vapor-compression-based predecessors. We will explore materials in which caloric effects are generated by magnetostructural transitions driven by magnetic field, or magnetocaloric effects, and/or driven by pressure, i.e., barocaloric effects.

In this collaborative effort between Louisiana State University and Southern Illinois University, we will study phase transitions in three classes of materials that generate solid-state caloric effects near room temperature: (i) MnTX (T = Ni, Fe, Co and X = Si, Ge) compounds, which will be fabricated using high-pressure synthesis and thermal quenching methods to form metastable high-temperature/pressure phases, potentially resulting in magnetostructural transitions and large magnetocaloric effects in these systems; (ii) Bi-doped Ni-Mn-In Heusler alloys, for which we will investigate transport properties, including anomalous Hall effects, to understand field-induced magnetostructural transitions in this system, and (iii) Mn-based antiperovskites Mn₃XC (X = Zn, Ga, Ge, Sn) and Fe_nGeTe₂-based two-dimensional (2D) van der Waals ferromagnets, both of which show emergent behaviors, and can be considered as magnetic quantum materials. These materials exhibit a variety of magnetic transitions, and we will investigate the effects of doping, synthesis methods, and applied hydrostatic pressure on the phase transitions, and the solid-state caloric effects they generate.

The objectives of this project are the following: (i) to develop new metastable solid-state caloric MnTX materials, and to understand the underlying physics of the phase transitions in these systems; (ii) to investigate the transport properties, including anomalous Hall effects, of Bi-doped Ni-Mn-In Heusler alloys in order to obtain a better understanding of the underlying physics of field-induced magnetostructural transitions in these materials; and (iii) to explore phase transitions in, and magnetocaloric properties of, Mn₃XC alloys and Fe_nGeTe₂ 2-D van der Waals ferromagnets, both of which can be considered as quantum materials.

The scientific outcomes include: (i) the development of new magnetocaloric and multifunctional materials; (ii) a deeper understanding of the physics of the phase transitions responsible for multicaloric and multifunctional behaviors; and (iii) the discovery of new physical phenomena in metastable alloy phases and magnetic quantum materials.

The discovery of a practical and effective solid-state refrigeration material will lead to more efficient cooling systems. The impact of this could be profound: it would be a significant step toward energy independence and a cleaner environment, as cooling is one of our most energy-demanding technologies.