Magnetic excitations in long-range stripe-ordered \nPr2NiO4+δ

Abstract

We report an inelastic neutron scattering study on the magnetic excitations of ${\\mathrm{Pr}}_{2}{\\mathrm{NiO}}_{4+\\ensuremath{\\delta}}$ ($\\ensuremath{\\delta}\\ensuremath{\\sim}0.24\\ifmmode\\pm\\else\\textpm\\fi{}0.01$) at $T=10$ K. Spin stripe ordering becomes pronounced below $\\ensuremath{\\sim}220$ K with an incommensurability $\\ensuremath{\\epsilon}\\ensuremath{\\approx}0.346$, and a strong influence of interstitial oxygen is identified on establishing a long-range spin stripe ordering. Apart from the Goldstone modes emerging from the magnetic satellites (${\\mathbf{q}}_{m}$), multiple homologous modes are observed along the spin stripe modulation separated by $\\mathrm{\\ensuremath{\\Delta}}{\\mathbf{q}}_{m}\\ensuremath{\\approx}0.076$ in reciprocal lattice units, which is interpreted by the internal periodicity of the long-range ordered discommensurated spin stripes.