Inelastic neutron scattering study of magnetic excitations in the helimagnetic and antiferromagnetic phases of NiBr2 |
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Authors: | P Day MW Moore TE Wood DMcK Paul KRA Ziebeck LP Regnault J Rossat-Mignod |
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Institution: | 1. Oxford University, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, England;2. Institut Laue-Langevin, B.P. 156 Centre de tri, 38042 Grenoble Cedex, France;3. Laboratoire de Diffraction Neutronique, Departement de Recherche Fondamentale, Centre d''Etudes Nucleaires, B.P. 85, 38041 Grenoble Cedex, France |
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Abstract: | The spin wave dispersion in NiBr2 has been studied by medium and long wavelength inelastic neutron scattering in the 1 1 0], 1 0 0] and 0 0 1] directions at 4.2 and 30 K, i.e. in the incommensurate helical and collinear antiferromagnetic phases. The values of the intralayer Heisenberg exchange constant Jij and XY anisotropy constant D at 4.2(30) K are J01 0.379(1)(0.379(1)), J02 0.0036(50)(0.0036(50)), J03 - 0.105(5) (?0.105(5)), J′ - 0.0423(50)(?0.389(50))D 0.0364(50)(0.0290(50)), where J′; is the interlayer exchange constant. In fitting the 4.2 K data account is taken of the co-existence of three equivalent domains and of intensity arising from and where is the wavevector of the helix. In the low frequency region of the dispersion curve such peaks are resolved. The results reinforce the hypothesis that in zero-field the commensurate-incommensurate phase transition is driven by fluctuations. |
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