A tin-119 and gadolinium-155 Moessbauer spectroscopy and neutron diffraction study of R3T4X4 (R = rare-earth, T = copper, silver, X = tin, germanium) compounds

The isostructural R3T4X4 (R: rare earth, T:Mn,Pd,Cu,Ag, X:Si,Ge,Sn) family of compounds have been extensively studied recently due to the rich variety of magnetic behaviour exhibited: the two rare earth sublattices often order with quite different moment values and distinct magnetic structures. In some cases the rare earth sites will also have quite different ordering temperatures. Several of the series, R 3Cu4Sn4 and R3Ag4Sn 4 and R3Cu4Ge4, appear not to follow the expected de Gennes scaling law of transition temperatures despite the structural uniformity of the system. Moreover, the system suffers from a common problem in rare earth intermetallic systems: an important lack of data and understanding of the Sm and Gd members.;We find that a simple isotropic hyperfine field transfer model successfully describes the 119Sn Mössbauer spectra of several R 3T4Sn4 (T:Cu,Ag) compounds. 119Sn Mössbauer spectroscopy also reveals important magnetic interactions previously missed: Nd3Cu4Sn4 data exhibits a clear magnetic contribution at temperatures at which neutron diffraction data did not, while Ho3Cu4Sn4 exhibited magnetic interactions above the ordering temperature determined by neutron diffraction. The Sm 3Ag4Sn4 and Sm3Cu4Sn 4 compounds proved to behave entirely differently than previously thought: the former undergoes magnetic ordering at 26K rather than 9K, and shows evidence of anisotropic field transfer, while Sm3Cu4Sn4 fails to order and instead exhibits slow moment dynamics. The Gd compounds also yield surprising results as Gd3Cu4Ge4 and Gd3Ag4Sn4 order at far higher temperature than previously thought, while Gd3Cu4Sn4 exhibits the most complex 119Sn Mössbauer spectrum due only to the moments at the Gd-2d site.;The R3T4X4 system remains highly magnetically complex and diverse, however the magnetic landscape has been significantly altered. The flat plate mounting technique for neutron diffraction, especially when combined with Mössbauer spectroscopy data, allows for the determination of the magnetic structures of Sm3Ag4Sn4 as well as Gd3Ag4Sn4 and partially of Gd 3Cu4Sn4, showing great promise as an important new experimental tool.;Capitalizing on the presence of Sn in many of these compounds, we have used 119Sn Mössbauer spectroscopy as a probe of local magnetism at the Sn sites in the structure. Although Sn carries no magnetic moment, a transferred field from the rare earth neighbours is observed, as both Sn sites in the structure have nearest neighbours from both rare earth sublattices. We also performed 155Gd Mössbauer spectroscopy on three Gd compounds, probing the local magnetism at the 155Gd nuclei directly. Using the newly developed flat plate mounting for highly absorbing samples, we performed neutron diffraction on several Sm and Gd compounds to probe the long range spatial symmetry of the rare earth magnetic moments. The Mössbauer spectroscopy and neutron scattering results were then combined as verification of consistency, but more importantly as complementary sources of magnetic information allowing us to draw conclusions that otherwise could not be drawn with either of the experimental techniques alone.