Figure 2: Neutron spectroscopy study of magnetic excitations.

(a–f) Inelastic neutron-scattering intensities for La_1.6Sr_0.4CoO₄ and La_1.5Sr_0.5CoO₄ measured at the 2 T spectrometer. (a,b) Neutron-scattering intensities (shifted by a value indicated by the horizontal bars); circles: diagonal scans across (1/2 1/2 0) in a and (3/2 1/2 0) in b as a function of H; diamonds: (H 0.5 0) scans plotted as a function of H-1 and H in a and b, respectively; solid lines were derived from symmetric gaussian fits. (c–f) Intensity maps as a function of Q and energy transfer through (3/2 1/2 0) in [1 0 0] direction (c,d) and [1 1 0] direction (e,f). Maps have been generated from the data above (colours between two data points are interpolated). Dashed lines are guide to the eyes (c,e) and dispersions derived from spin wave calculations (d,f); black/dashed circles: spurious peaks/phonons. Error bars for all data included (might be smaller than symbol size). (g–o) Constant-energy maps measured the IN8 spectrometer (energy written to the left of each map). H (K) is ranging from 1 to 2 (from 0 to 1) from left to right (from bottom to top) in each map. Instead of interpolation, the whole area around one measured data point is filled with the same colour. Fits of the dispersion (diamonds) that have been derived from these maps are also included in c and e. In n and o, the background was subtracted (see Methods Section). (p) Constant-Q scan at (3/2 1/2 0). (q) Constant-Q scans at (1/2−ε 1/2+ε 0) measured at ~10 K at a cold neutron TAS (blue circles); in addition, the background is shown (green circles). Intensity error bars are statistical error bars calculated by the square root of intensity. Other error bars are s.d. obtained from Gaussian peak fits.