Fig. 1
From: Expansion of the spin cycloid in multiferroic BiFeO3 thin films
Presence of the cycloid in 50 nm thick films. a Neutron diffraction reciprocal space map of the 50 nm 2% Co-doped BFO film around the G-type antiferromagnetic \((\frac{1}{2}\frac{1}{2}\frac{1}{2})\) Bragg reflection. The double peak at (0.485, 0.485, 0.5) arises from an incommensurate spin structure, i.e., the spin cycloid. The positions of the two peak maxima indicate the propagation direction of the spin cycloid, which is along \([11\bar 2]\) in contrast to \([1\bar 10]\) as in bulk BFO. In addition, a peak at precisely QHK = \((\frac{1}{2}\frac{1}{2}\frac{1}{2})\), caused by second-order contaminations from the substrate, is present. The inset shows the neutron RSM in the reciprocal \((\frac{1}{2}\frac{1}{2}\overline {\frac{1}{2}} )\) direction, where only one single peak is present. b Simulation of the neutron diffraction data of the 50 nm film using a length of the spin cycloid of λ0 = 84 nm. c Neutron diffraction data along \([11\bar 2]\) through the antiferromagnetic Bragg peaks for both orientations \((\frac{1}{2}\frac{1}{2}\frac{1}{2})\) and \((\frac{1}{2}\frac{1}{2}\overline {\frac{1}{2}} )\). Dashed lines are fits of Gaussian line profiles to the experimental data while the solid line was extracted from the simulation shown in b. The error bars correspond to 1 s.d. of the count rate. d X-ray RSM around the (221) reflection demonstrates the single domain growth and further indicates the expansion of the BFO lattice parameter perpendicular to the film plane. e–h Corresponding data of the 192 nm 2% Co-doped BFO film. Note, in (c, g) for the \((\frac{1}{2}\frac{1}{2}\overline {\frac{1}{2}} )\) data a weak second-order contamination (termed λ/2) originating from the substrate, is also present. All neutron diffraction data were taken at a temperature of 150 K
