Kyle Wetzlar

Electric field induced magnetization rotation in patterned Ni ring/Pb(Mg1/3Nb2/3)O3](1−0.32)-[PbTiO3]0.32 heterostructures

Electric field induced magnetoelastic anisotropy is shown to rotate the magnetization of a ring-shaped magnet by 90° in a Ni ring/(011) Pb(Mg1/3Nb2/3)O3](1−0.32)-[PbTiO3]0.32 heterostructure. The 2000 nm diameter ring is initially field annealed forming the “onion” magnetization state. A 0.8 MV/m electric field is applied to the substrate creating anisotropic piezostrain and a perpendicular in-plane easy axis. Magnetic force microscopy confirms the 90° rotation of the vortex-type domain walls from the field annealing direction. Rotations are stable without electric field due to remnant strains induced during the poling process, supporting the viability of strain-based magnetic recording methods.

Electrically Driven Magnetic Domain Wall Rotation in Multiferroic Heterostructures to Manipulate Suspended On-Chip Magnetic Particles

In this work, we experimentally demonstrate deterministic electrically driven, strain-mediated domain wall (DW) rotation in ferromagnetic Ni rings fabricated on piezoelectric [Pb(Mg1/3Nb2/3)O3]0.66-[PbTiO3]0.34 (PMN-PT) substrates. While simultaneously imaging the Ni rings with X-ray magnetic circular dichroism photoemission electron microscopy, an electric field is applied across the PMN-PT substrate that induces strain in the ring structures, driving DW rotation around the ring toward the dominant PMN-PT strain axis by the inverse magnetostriction effect. The DW rotation we observe is analytically predicted using a fully coupled micromagnetic/elastodynamic multiphysics simulation, which verifies that the experimental behavior is caused by the electrically generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate micrometer-scale magnetic beads in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications.

Thermomagnetic conversion efficiencies for ferromagnetic materials

The theory of thermomagnetic generation is reviewed and an efficiency analysis using experimentally measured magneto-thermal properties of 3d transitional and 4f rare earth ferromagnetic elements is presented in this study. While theoretical results suggest that 55% of Carnot efficiency is possible, experimental data indicate values smaller than 25% of Carnot efficiency unless large magnetic field (e.g., Ha ∼ 80 kOe) is applied. For smaller magnetic fields representative of NdFeB permanent magnets (e.g., Ha = 3 kOe), the largest efficiencies are obtained for operating ferromagnetic materials over a smaller temperature difference (ΔT = 5 K). Furthermore, single crystal materials are found to have superior efficiencies, as do elements that undergo an order-to-order phase transition. Both of these later results relate to increased magnetization changes over a given ΔT. These results are subsequently used to postulate that a single domain structure will produce larger efficiencies due to the higher magnetizat...

Electrically controlled reversible and hysteretic magnetic domain evolution in nickel film/Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (011) heterostructure

We report direct Lorentz microscopy observations of electrically induced magnetic domain motion in a nickel film/Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-PT (011)) heterostructure. The 0.5 mm-thick PMN-PT substrate contains a 10 μm-wide, 60 nm-thick Ni/Pt electron-permeable observation region. Stress from the substrate creates magnetoelastic anisotropy of up to 4 kJ m−3 in the nickel film resulting in reversible magnetization rotation as well as non-reversible domain wall jumps (i.e., Barkhausen jumps). The observed magnetization of the film is directly related to the local strain gradient as computed by the finite element method, providing strong evidence of the effectiveness of the strain-mediated magnetoelectric approach for device applications.

Rotating Fuel Tank Design to Attenuate Fluid Sloshing in Microgravity

The problem of fluid slosh is one that continues to plague space vehicles to this very day. This report presents an initial investigation of one potential solution: a rotating, tapered cylinder, fluid container with helical baffles. This geometry combines the benefits of an increasing radial cross-section along the axis of rotation with an Archimedes Screw to bring the fluid into a stable equilibrium capable of quickly attenuating slosh. Experiments were performed on two tank geometries, one with and one without helical baffles, to gauge their benefits independently at various rotation rates, subject to slosh imparted by a transition between 2 g acceleration and microgravity. Using these procedures, coupled with video analysis software, the settling time, or time to achieve an equilibrium fluid/vapor separation, and the damping coefficient were determined for both tanks at rotation rates between 0 and 156 RPM. While both tank geometries were capable of damping the imparted slosh, it was found that the helical baffles decreased the required settling time by an average of 57.6% and increased the damping ratio by an average of 53.5%. With these apparent slosh damping benefits in mind, we recommend that further investigation be conducted to explore this fluid extraction method as well as the scalability between different tank fill levels and sizes.