Neutron scattering length of terbium structure refinement and magnetic moments of terbium iron garnet

Abstract

The neutron scattering length of terbium was redetermined from powder data on terbium iron garnet (TbIG) and TbO 2 by the profile analysis technique. The mean value obtained is b ( Tb) = 0.735(10) x 10 −12 cm. Furthermore the positional and thermal parameters of TbIG have been refined from single crystal X-ray and neutron powder data. The results from both experiments agree well. The X-ray data from a sphere of diameter φ = 282 μm were collected by Mo Kα radiation. The refinement was carried out including an extinction parameter which was also applied to correct for anomalous transmission. The powder data were treated by the profile analysis technique where the structural parameters and the magnetic moments were refined simultaneously. Two slightly different form factor curves were applied for Fe 3+ in the crystallographic sites. The magnetic moments for the iron ions were found to be μ = 3.69(10) μ B for the octahedral and 3.65(10) μ B for the tetrahedral site at room temperature. The moment for terbium is μ = 1.15(09) μ B and the whole magnetisation for one formula unit is 0.12(0.40) μ B . The observed moments of Fe 3+ are considerably reduced as compared to the free ion spin only value which was calculated from a Brillouin function for S = 5 2 to be 4.34 μ B at 300 K.