Identification of features in the powder pattern of the antiferromagnet FePS3 using polarization analysis with energy analysis

Recent powder patterns of the antiferromagnet FePS3 below its Neel temperature show unusual magnetic diffuse intensity in the Q range 0.5-0.8 Angstrom(-1). This was initially thought to be a group of unresolved magnetic Bragg peaks. However subsequent powder patterns taken with longer wavelengths and better resolution have failed to resolve the peaks except to confirm the existence of a Bragg peak at Q = 0.61 Angstrom(-1). In particular the powder pattern taken with lambda = 5 Angstrom neutrons shows a marked diminution of the rest of the diffuse intensity with respect to this Bragg peak. To test whether the diffuse intensity is due to magnon scattering, the low Q region of the scattering from the powder sample of FePS3 was measured on LONGPOL at 100 K with both polarization and energy analysis. The diffuse intensity was confirmed as magnetic but energy analysis showed, that it is at least overwhelmingly elastic with no suggestion of scattering with an energy gain of 13 meV, the energy expected for the magnon band gap in this highly anisotropic antiferromagnet. (C) 2003 Elsevier Science B.V. All rights reserved.