Short-range order of Br and three-dimensional magnetism in (CuBr)LaNb 2O 7

Alexander A. Tsirlin, Artem M. Abakumov, Clemens Ritter, Paul F. Henry, Oleg Janson, Helge Rosner

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8 Citations (Scopus)


We present a comprehensive study of the crystal structure, magnetic structure, and microscopic magnetic model of (CuBr)LaNb 2O 7, the Br analog of the spin-gap quantum magnet (CuCl)LaNb 2O 7. Despite similar crystal structures and spin lattices, the magnetic behavior and even peculiarities of the atomic arrangement in the Cl and Br compounds are very different. The high-resolution x-ray and neutron data reveal a split position of Br atoms in (CuBr)LaNb 2O 7. This splitting originates from two possible configurations developed by [CuBr] zigzag ribbons. While the Br atoms are locally ordered in the ab plane, their arrangement along the c direction remains partially disordered. The predominant and energetically more favorable configuration features an additional doubling of the c lattice parameter that was not observed in (CuCl)LaNb 2O 7. (CuBr)LaNb 2O 7 undergoes long-range antiferromagnetic ordering at T N=32 K, which is nearly 70% of the leading exchange coupling J 4≃48 K. The Br compound does not show any experimental signatures of low-dimensional magnetism because the underlying spin lattice is three-dimensional. The coupling along the c direction is comparable to the couplings in the ab plane, even though the shortest Cu-Cu distance along c (11.69 Å) is three times larger than nearest-neighbor distances in the ab plane (3.55 Å). The stripe antiferromagnetic long-range order featuring columns of parallel spins in the ab plane and antiparallel spins along c is verified experimentally and confirmed by the microscopic analysis.

Original languageEnglish
Article number214427
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number21
Publication statusPublished - 22 Jun 2012
Externally publishedYes


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