Materials with strongly correlated electrons have been extensively studied because of the novel and often technologically useful properties that arise due to the interplay between spin, lattice, charge, and orbital degrees of freedom. [1] When one or more of these degrees of freedom is not allowed to attain a low-energy ground state, either due to competing interactions or the geometry of the lattice, a degree of local disorder arises and the material is said to be frustrated. [2–4]

The work presented here aims to develop an understanding of how this frustration in complex oxides affects the physical properties via careful study in a variety of structures. Through the use of detailed structural characterization; X-ray and neutron diffraction in conjunction with physical property measurements and in some cases Density Functional Theory (DFT) calculations, we explore the relationship between crystal structure and macroscopic properties.

Firstly we examine the solid solution Zn_1-xCo _xCr₂O₄. By introducing magnetism onto an otherwise non-magnetic diamond lattice, we construct a phase diagram that shows the evolution of spiral magnetic order for concentrations of Co above x =0.5. We then discuss the solid solution CoAl _2-xGa_xO ₄. We examine how site mixing between the tetrahedral and octahedral sites and lattice expansion affect frustration in CoAl₂O₄ . We demonstrate that increasing the unit cell volume, and correspondingly increasing the length of superexchange pathways, reduces Θ _CW and that site mixing alters the shape of the inverse magnetic susceptibility curves.

We then present an investigation into several magnetic chain compounds which experience a competition between nearest and next-nearest neighbor interactions. We begin by examining CoSeO₄ and CoSe₂O₅. Both display complex magnetism including weak ferromagnetism and field-induced transitions. We also show that CoSeO₄ demonstrates magnetodielectric coupling. We conclude by presenting work on the polar ferri-magnet VOSe ₂O₅. Using a combination of DFT calculations and powder neutron diffraction we suggest a complex ferrimagnetic spin structure sets in at low temperatures with interesting dielectric properties at higher temperature.