The series Cs2CuCl4-xBrx (02CuBr4
[1,2,3].
Latest experiments show, that at growth temperatures of 50°C the whole compositional range can be stabilized in the
orthorhombic space group Pnma [4], whereas at lower growth temperatures of 24°C a structural phase transition into an
apparently tetragonal phase with layers formed by edge connected CuCl6 octahedrons can be observed in the range from
0.9 < x < 1.9.
The strongest magnetic interactions exist between the Cu2+ ions (S=1/2) in the bc-plane and are transmitted by surrounding
halogen ions via the exchange path Cu-X-X-Cu (X=halogen atom), in a way that the magnetic exchange is strongly
influenced by the position of the halogen ions within the tetrahedrons.
To shed more light on the structural origin of the magnetic interactions the position of Cl and Br ions was determined by a
neutron single crystal diffraction experiment at the diffractometer HEIDI at the neutron source FRM II. Three single crystals of
different composition (x=1, 1.2 and 3.2) were measured at 300K. Structural refinement of the data reveals the fact that doping
Cs2CuCl4 with Br affects preferably the position with the smallest exchange interaction, in such a way that the disturbance of
the magnetic exchange path is kept as small as possible.
[1] T. Ono, et al., Phys. Rev. B 67, 104431 (2003)
[2] R. Coldea, et al., Phys.Rev.Lett. 86, 1335 (2000)
[3] T. Radu, et al. , Phys.Rev.Lett. 95,127202 (2005)
[4] N. Krüger et al., Cryst. Growth Des., 10, 4456-4462 (2010)
|
