UCLA

Nanostrutured magnetic materials have gained much recent interest because of their application in various electronic systems. These materials, however, often require complex lithography and epitaxy to control the magnetic properties. In this work, solution-phase self-assembly is used to create magnetic and magnetoelectric materials with a variety of nanoscale structures. By engineering the architecture of the system, control over a range of magnetic properties can be realized.

The first part of this work focuses on nano-magnetic materials. Here, the organization of nanoscale magnets into different geometries is controlled, and the properties of the systems are studied. In the first chapter, Ni-Cu nanowire stacks are examined to explore the effect of shape anisotropy on the coupling between different elements. This work provides insight into how to design new elements for spin-torque devices. In the next chapter, directed self-assembly of block copolymers is used to create coupled 1D chains of ferromagnetic and superparamagnetic FePt nanoparticles. These nano-patterned are globally aligned on the wafer length-scale using micron-sized lithographic grooves. This system is ideal for studying dipolar coupling between magnetic nanocrystals. Additionally, the processing methods developed here provide a platform for organizing other types of nanomaterials.

The second sections explore magnetoelectric materials. These are materials that combine ferromagnetism and ferroelectricity in a coupled manner. One material that does this intrinsically is bismuth ferrite. The first chapter of this section explores ordered nanoporous bismuth ferrite produced by block copolymer templating. It is shown that the ordered porosity of the system creates a unique strain state in the bismuth ferrite, which in turn produces a large change in magnetization upon application of an electric field. Finally, in the last chapter, a nanostructured composite magnetoelectric system is studied. Here, magnetostrictive Ni nanocrystals are coupled to a single-crystalline piezoelectric substrate. The nanocrystals are superparamagnetic and show no net magnetization. Upon application of an electric field, however, strain induced in the piezoelectric substrate strains the lattice of the nanocrystals, creating a preferred magnetic axis along the high strained direction. This locks the magnetization along the strain axis and switches the nanocrystals from a superparamagnetic to a ferromagnetic state.