Application of the Inverted-Neutron-Filter Technique to the Study of Inelastic Scattering by Paramagnetic Substances

Using the filter-cutoff method we have measured the quasielastic scattering of slow neutrons from several paramagnetic compounds. Our results for Mn${\mathrm{F}}_2$ at large scattering angles are in reasonable agreement with time-of-flight measurements by Cribier and Jacrot. For small scattering angles we have confirmed the Lorentz-like form of the energy distribution of scattered neutrons predicted by de Gennes. Similar measurements at large and small scattering angles on a partially inverted sample of Mn${\mathrm{Al}}_2$ ${\mathrm{O}}_4$ did not exhibit the predicted angular dependence. This suggests that the assumption of $A-A$ interactions only is inappropriate for this compound. From the temperature dependence of the intensity of the (200) magnetic reflection, a Néel temperature of 18°K was deduced for the Mn${\mathrm{Al}}_2$ ${\mathrm{O}}_4$. Our results demonstrate that with an adequate flux of long-wavelength neutrons the inverted-filter technique can be employed successfully in studies of paramagnetic scattering.