Multiferroic/magnetoelectric materials have received substantial attention for memory applications. Among many studies, only one has used a two-phase magnetoelectric layered structure which has a far superior converse magnetoelectric effect (superior performance as a memory) when compared to single-phase materials and particulate composites. However, previous measurements studied on macroscopic properties rather than microscopic properties (local magnetization/domain-structure information required for memory bit). In this dissertation, the electrical control of a nanoscale magnetic domain-structure in magnetoelectric Ni/PZT layered thin film and Ni-microdot/PZT-film layered structures is evaluated with microscopic characterizations. The electric-field-induced nanoscale magnetic domain transformations (domain-wall and vortex-core motions) are observed with Magnetic Force Microscope (MFM). The average feature size which the domain structure can be transformed between two stable configurations as a memory bit is approximately 300∼500 nm for the materials studied.

The development and control of nanoscale magnetic fields, preferably with electrical fields, remains one of the dominant challenges facing science. Recently, a “Multiferroic/Magnetoelectric Quantum Electromagnet” theoretical model suggested that the spin-structure could be altered with an electric field due to the converse magnetoelectric effect in a multiferroic/magnetoelectric thin film (a concept similar to nanoscale electromagnet). Based on these and other theoretical models, a nanoscale magnetoelectric system employing spin-structure/single-domain concept is studied as a mechanism to generate/control nanoscale magnetic fields. Experimental results on a magnetoelectric Ni-nanobar/PZT-film layered structure demonstrating control of a single-domain/spin-structure evolution with an electric field due to the converse magnetoelectric effect is presented. The reversible single-domain/spin-structure evolution from an initial single-domain/spin-structure state to a transitional S-shape single-domain/spin-structure state with an electric field was observed with MFM. The electric-field-induced domain patterns are similar as the magnetic-field-induced domain patterns (the magnetic domain structure can be changed with an external magnetic field and also controlled by an electric field). These results confirm the hypothesis that reorientation of a spin-structure/single-domain in the nanoscale is achievable and subsequent control of the local magnetic field is possible.

In addition to memory and nano-electromagnet, a magnetoelectric layered structure with the magnetoelectric effect used in a mechanical-vibration-based energy harvester is evaluated. This result provides the first step in developing a future nanoscale magnetoelectric energy harvester.