Pyrochlore Titanates

Neutron diffraction is performed on spin ice thin films of thicknesses ranging between 40 - 400 nm, a scattering map taken on a 400 nm film at T = 0.1 K in B = 5 T is shown on the left. For all of the measured films Bragg peaks that signal magnetic field induced long range order are observed at mK temperatures. The Bragg peaks occur at the zone center positions (indicated by the black dots in the schematic on the right) resulting from a Q = 0 phase that has a two-in/two-out spin texture on each tetrahedron with two of the four spins on the tetrahedron polarized along the field direction. In the scattering map shown diffuse peaks are not observed at the zone boundary positions (Q = X phase). For more details see Barry et al. Phys. Rev. Materials, 3, 084412 (2019) "Modification of spin-ice physics in Ho2Ti2O7 thin films"

Spinel Vanadates

The Beekman group used neutron diffraction to determine the magnetic ground state of spinel vanadate thin films. In the figure diffraction peak intensities are shown for the (111) peak as a function of temperature, which shows a clear temperature dependence. The figure clearly shows that the substrate peaks (structural) can provide large responses that can sometimes obscure the film peaks. The order parameter scan of the film reflection shows a transition to a magnetically ordered state (collinear ferrimagnetic) at 150 K. From monitoring other peak intensities down to 10 K the ground state was determined to be a noncollinear state with the spin tecture indicated in the figure (larger moments on the Co and smaller moments on the V). Surprisingly, the ground state is a purely planar texture with the V-spins canting away from the direction antiparallel to the Co. This is surprising because the measurement was doen on a very thick (400 nm) film, clearly showing that even in thick films the structural distortions introduce by strain severly alter the magnetic anisotropy in the film. For more details see Thompson et al. Phys. Rev. Materials, 2, 104411 (2018) "Spin canting and orbital order in spinel vanadate thin films"