Revealing magnetic domain structure in functional Fe2.5Zn0.5O4 wires by transmission electron microscopy

The magnetic and crystallographic microstructures in Fe2.5Zn0.5O4 (FZO) wires fabricated using nano-imprint lithography, pulsed laser deposition and a molybdenum lift-off mask technique were studied by transmission electron microscopy (TEM). A process using a focused ion beam completely separated the FZO wires from the insulating MgO substrate, and accordingly allowed in-depth TEM studies of the domain structures. Observations using energy-filtered TEM demonstrated good crystallinity of the FZO wires. Both Lorentz microscopy and electron holography studies revealed unexpectedly small magnetic domains (∼100 nm or smaller) due to a significant interaction with antiphase boundaries. The role of antiphase boundaries on the functionalities observed in the constrained wires (e.g., nonlinear I-V characteristics and large magnetoresistance) is discussed on the basis of these microscopic observations.