Resolving Effects of the Commensurate to Incommensurate Crossover on the Magnetism in Charge-Stripe Ordered La2-xSrxNiO4

Abstract

The La-based cuprates are the original high high-temperature superconductors, and are some of most highly researched cuprates in terms of the magnetic excitations. Unlike other holed doped cuprates, superconductivity in La-based cuprates only results in a partial gapping of the magnetic excitation spectrum[1,2]. With magnetic excitations extending to lower energies in La-based cuprates, their low energy excitations bare a close similarity to those of charge-stripe ordered materials such as insulating La2-xSrxNiO4+d, such that the magnetism of the two materials are often compared and contrasted[3]. Our understanding of the magnetism of charge-stripe ordered La2-xSrxNiO4+d is limited to detailed studies of the magnetic order[4-6], complemented by studies of the magnetic excitations on a small number of doping levels primarily at base temperatures, see for example: [7-9]. We have undertook combined neutron diffraction and inelastic scattering studies of doping levels around the commensurate third doping level. We will show how our combined systematic high resolution cold neutron scattering, and thermal neutron scattering mapping of the magnetic excitations to temperatures beyond the magnetic ordering, illuminates new understanding of the magnetic interactions of charge-stripe ordered La2-xSrxNiO4+d. We will discuss the role of magnetism in the ordering process, beyond the role played by charge interactions [10]. Furthermore, we will discuss the role of the crossover between commensurate charge-stripe order and incommensurate charge-stripe order on the magnetic interactions of La2-xSrxNiO4+d, with competing models proposed [11,12].