$\mathrm{MnO}$ spin-wave dispersion curves from neutron powder diffraction

We describe a model-independent approach for the extraction of spin-wave dispersion curves from powder neutron total scattering data. Our approach is based on a statistical analysis of real-space spin configurations to calculate spin-dynamical quantities. The RMCPROFILE implementation of the reverse Monte Carlo refinement process is used to generate a large ensemble of supercell spin configurations from $\mathrm{MnO}$ powder diffraction data collected at $100\mathrm{K}$. Our analysis of these configurations gives spin-wave dispersion curves for $\mathrm{MnO}$ that agree well with those determined independently using neutron triple-axis spectroscopic techniques.

Figure 1

$\mathrm{MnO}$ spin-wave dispersion curves calculated using Eq. (33) (solid lines), and extracted from our spin Monte Carlo simulations using the method developed in the text (open circles).

Figure 2

(Color online) $\mathrm{MnO}$ spin-wave dispersion curves calculated from our RMC configurations (data points). Fits to the INS data of Pepy (Ref. 20) (shaded regions, $88.75\mathrm{K}\le T\le 113.75\mathrm{K}$) and of Kohgi (Ref. 21) (red dashed lines, $T=100\mathrm{K}$) are included for comparison. The relevant directions in reciprocal space are illustrated on a $(1\overline{1}0{)}^{*}$ section of the $\mathrm{MnO}$ reciprocal lattice.