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College Park, Maryland      June 6 - 10 , 2004

TP51: Neutron Diffraction Studies of the Tb5(SixGe1-x)4 Magnetoelastic Compounds

J. L. Zarestky, V. O. Garlea (Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011), C. Y. Jones (National Institute of Standards and Technology), D. L. Schlagel, T. A. Lograsso, A. O. Pecharsky (Materials and Engineering Physics Program, Ames Laboratory, Ames, Iowa, 50011), V. K. Pecharsky, K. A. Gschneidner Jr. (Materials and Engineering Physics Program, Ames Laboratory, Ames, Iowa, 50011; Dept. of Materials Science and Engineering, Iowa State University, Ames, Iowa, 50011), C. Stassis (Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011)

The R5(SixGe1-x)4 [1] pseudobinary alloys exhibit a number of diverse and unique properties associated with both their naturally layered crystal structures and the combined magnetic-crystallographic transformations at low temperatures. In particular, this family of compounds is attractive for its potential applications as a magnetic refrigerant and/or magnetostrictive and magnetoresistive transducers. Progress in understanding the properties of these compounds has been hindered by the difficulty of growing single crystals. Recently a single crystal of Tb5Si2.2Ge1.8 was grown at the Ames Laboratory and this motivated us to initiate a neutron diffraction study of this compound as a function of temperature. The single crystal measurements were performed using the HB1A triple axis spectrometer at the High Flux Isotope Reactor (HFIR). The measurements performed in the a-c and a-b planes indicate the occurrence, at approximately 115 K, of a phase transition from monoclinic/paramagnetic to an orthorhombic/ferromagnetic structure. Below 50 K, a change in the intensities of selected reflections has been observed. In addition to the single crystal study, neutron powder diffraction measurements were also performed using the BT-1 powder diffractometer at the NIST Center for Neutron Research (NCNR). Models of the magnetic structure are used to interpret the experimental results.

[1] V.K.Pecharsky, K.A.Gschneidner Jr., Phys. Rev. Lett. 78 (1997) 4494

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