Dr. Peter Müllner
When exposed to a magnetic field, magnetic shape memory (MSM) alloys deform by twinning. The interaction between magnetic domains and twin boundaries affects the mobility and motion of twin boundaries in a dynamical magnetic field. This study examines the magneto-structural interactions that affect magneto-mechanical properties of the MSM alloy nickel-manganese-gallium (Ni-Mn-Ga). We assessed the progression of magnetic domains, the interaction of magnetic domains with twin boundaries, and the distribution of magnetic energies with computational methods. We performed micromagnetics simulations with a Fortran code, where we varied elements of the system such as orientation and magnitude of the magnetic field, placement of a twin boundary in the sample, number of twins, and declaration of the c-axis orientation. Twin boundary motion and c-axis reorientation of the tetragonal crystal lattice cause the resultant shape change. With sufficient magnetocrystalline anisotropy energy, the c-axis rotates, causing a shrinkage across the twin. While the magnetic field is applied, magnetic domains grow, thus determining the magnetic structure of the crystal. Simulation outputs included domain structures obtained using MATLAB, and energy distribution plots acquired using Python. The results of this study inform specific experimental parameters to improve the performance of Ni-Mn-Ga transducers in actuators or micropumps.
Adams, Claire L.; Veligatla, Medha; and Müllner, Peter, "Magneto-Structural Interactions of Magnetic Shape Memory Alloy Ni-Mn-Ga" (2020). 2020 Undergraduate Research Showcase. 1.