Understanding and controlling the interactions of magnetic nanostructures

The understanding and control of magnetic interactions at the nanoscale regime is important for applications in ultra-high density magnetic data storage, memory and spintronic devices. In this dissertation, a variety of works will explore the creation of novel magnetic nanostructures and the interactions of these materials at the nanoscale. The first part examines how the hierarchical organization of magnetic nanocrystals is a powerful method for tuning domain interactions. In this work, hard (ferromagnetic) and soft (superparamagnetic) FePt nanocrystals are stacked inside 1-D arrays of a mesoporous silica host matrix in order to induce constructive dipole coupling between particles to form nanochains. The hard nanocrystal chains have higher magnetic energy compared to random agglomeration of nanoparticles due to constructive dipole coupling from 1-D confinement. Furthermore, by creating a stack of mixed hard and soft nanocrystal inside the chain, these superstructures gained the highest magnetic energy of all. By analyzing their magnetic properties with the pure hard FePt nanostacks, the enhancement in the magnetization reversal barrier of all nanochains can be decomposed into an enthalpic and entropic contribution.;In the second part of the dissertation, the inorganic/organic co-assembly method is utilized to create MFe2O4 (M=Zn, Ni, Mg, Co) spinets and multiferroic BiFeO3 mesoporous films that possess novel properties. In the ferrimagnetic ferrite systems, the stress and shape anisotropy imparted by the nanoscale architecture creates useful perpendicular magnetizations which are uncommonly observed in thin films. For the antiferromagnetic BiFeO 3 (BFO) films, the unique nanoscale structure with open porosity can be utilized as space for filling other magnetic metals to create exchanged coupled composite materials with interesting applications. Moreover, the higher surface area to volume ratio in nanoporous BFO films allows for more detectable magnetic surface spins. Most interestingly, the study between the mesoporous and dense BFO films show that the mesoporous films have a higher magnetoelectric coupling response. In summary, the combined dissertation work utilizes the creation of different nanostructured materials as a method to study the nanoscale interactions between magnetic domains in 1-D and 3-D geometries.