Magnetism and the Magnetic Excitations of Charge Ordered La2−xSrxNiO4+δ

Abstract of thesis submitted for the degree of Doctor of Philosophy In this thesis I present an investigation into the magnetic order and magnetic excitations of charge-ordered La2−xSrxNiO4+δ using magnetization and neutron scattering techniques. I have studied the magnetic ordering over a wide range of doping levels, 0 ≤ x ≤ 0.5, using magnetization measurements and neutron diffraction. I have compared my mag-netization study with earlier work carried out over a wider range of doping levels and with measurements at higher temperatures on similar doping levels. In the magnetization measurements I discovered unusual ‘memory ’ effects of the remnant magnetization. My neutron diffraction measurements go to lower temperatures than previous studies and extend the range of doping levels that have been studied. Inelastic neutron scattering was employed to study the spin wave excitations of charge-ordered La2−xSrxNiO4+δ, for charge-ordering with a period either commensurate or in-commensurate with the crystal lattice. The effect of incommensurate ordering on the exchange interactions was observed to be insignificant, with the excitations in the in