Publications (3)0 Total impact
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ABSTRACT: A combined neutron and x-ray diffraction study of TbBaFe2O5 reveals a rare
checkerboard to charge ordering transition. TbBaFe2O5 is a mixed valent
compound where Fe2+/Fe3+ ions are known to arrange into a stripe charge-ordered
state below TV = 291 K, that consists of alternating Fe2+/Fe3+ stripes in the
basal plane running along the b direction. Our measurements reveal that the
stripe charge-ordering is preceded by a checkerboard charge-ordered phase
between TV < T < T* = 308 K. The checkerboard ordering is stabilized by
inter-site coulomb interactions which give way to a stripe state stabilized by
orbital ordering.
10/2012;
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ABSTRACT: X-ray diffraction experiments were performed on polycrystalline and single-crystal specimens of Ce$_{2}$Fe$_{17}$ at temperatures between 10 K and 300 K. Below $T_{\mathrm{t}}$ = 118$\pm$2 K, additional weak superstructure reflections were observed in the antiferromagnetically ordered state. The superstructure can be described by a doubling of the chemical unit cell along the $\mathbf{c}$ direction in hexagonal notation with the same space group $R \bar{3} m$ as the room-temperature structure. The additional antiferromagnetic satellite reflections observed in earlier neutron diffraction experiments can be conclusively related to the appearance of this superstructure.
01/2007;
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ABSTRACT: Rare-earth-based permanent-magnet materials rich in iron have relatively low ferromagnetic ordering temperatures. This is believed to be due to the presence of antiferromagnetic exchange interactions, besides the ferromagnetic interactions responsible for the magnetic order. The magnetic properties of Ce2Fe17 are anomalous. Instead of ferromagnetic, it is antiferromagnetic, and instead of one ordering temperature, it shows two, at the Neel temperature TN ~ 208 K and at TT ~ 124 K. Ce2Fe17, doped by 0.5% Ta, also shows two ordering temperatures, one to an antiferromagnetic phase, at TN ~ 214 K, and one to a ferromagnetic phase, at T0 ~ 75 K. In order to clarify this behavior, single-crystalline samples were prepared by solution growth, and characterized by electron microscopy, single crystal x-ray diffraction, temperature-dependent specific heat, and magnetic field and temperature-dependent electrical resistivity and magnetization. From these measurements, magnetic H-T phase diagrams were determined for both Ta-doped Ce2Fe17 and undoped Ce2Fe17. These phase diagrams can be very well described in terms of a theory that gives magnetic phase diagrams of systems with competing antiferro- and ferromagnetism. Comment: 18 pages, 16 figures, submitted to PRB
12/2006;
