Chemical, magnetic, and orbital order of polycrystalline and thin film double perovskites

The work in this dissertation discusses the interplay between chemical, magnetic and orbital order. Polycrystalline double perovskites with isovalent A-cation substitutions are discussed in detail in Chapters 2 and 3. The crystal structure and physical properties are closely examined to understand the relationship between the two. In the second chapter the structural and magnetic properties of a perovskite system, BixLa2-xMnMO6 with M = Ni, Co for varying x is studied. It is seen that only less than 25% bismuth may be added to the perovskite and that some manganese substitutes onto the M site as Mn3+. Additionally the materials have magnetic and electrical properties, but these are not coupled to each other.;It is shown in Chapter 3 that isovalent substitutions can dramatically alter the physical properties, even when the substituted cations are not directly responsible for the behavior. In particular the double perovskite SrMn 0.5Ru0.5O3 has an antiferromagnetic C-type arrangement of magnetic spins. The addition of calcium in Sr(1-x)Ca(x) Mn0.5Ru0.5O3 for x ≥ 0.3 disrupts the orbitally-ordered driven system and resulting perovskites are ferromagnetic. The magnetization is much lower than expected for a genuine ferromagnet and neutron powder diffraction is suggestive of a complex magnetic arrangement.;The final chapter investigates the possibility of double perovskite materials as thin films for both technological and scientific exploration. Specifically the novel growth of three double perovskites, Sr2CrNbO6, Sr2GaNbO6, and Sr2GaTaO6 are investigated. Pulsed laser deposition on stoichiometric targets is used to grow thin films on single crystal substrates. A number of growth parameters are explored. A detailed X-ray diffraction is carried out to determine the phase purity and lattice constants. Additional techniques are used to further characterize the surface features and metal content.