Small-angle neutron scattering --- an invaluable tool to condensed matter studies

Mark Laver

Paul Scherrer Institut (PSI)

Switzerland

Small-angle neutron scattering (SANS) unveils invaluable information about the nanoscale magnetic profile in the bulk of systems. In this talk we review recent SANS work using both polarised and unpolarised neutron beams. First we see how magnetic domain walls --- both antiferromagnetic (AFM) and ferromagnetic --- may be imaged using SANS. Of particular interest is HoMnO3, a multiferroic material where an electric field was originally thought to induce bulk magnetic order. Our SANS experiments show that electric field actually changes the magnetization through shifting antiferromagnetic domain walls rather than altering bulk magnetic order. We also consider how SANS is invaluable in probing the superconducting state, through studies of the flux line (FL) lattice. By itself the FL system can be exploited as a test-bed for theories of structural order in solids and glasses, as discussed in an overview of recent explorations of superconductors ranging from elemental niobium to the pnictides and cuprates. The rich variety of astonishing FL lattice shapes exhibited by Nb and YBCO are presented in detail and we discuss what they reveal as to the underlying nature of these conventional and unconventional superconductors.