| Abstract
| - The long-range and short-range structures of KMgxCu1-xF3 (0 < x< 1) have been investigated by means ofXRPD and EPR. Two different solid solutions are present, based on the structure of KMgF3 (for x > 0.42)and of KCuF3 (for x< 0.26), respectively, and they are separated by a biphasic zone. Positional disorder isinduced by doping due to the different Cu and Mg environments. In fact, the EPR measurements have shownthat the Cu environment is isotropic for x > 0.8. It shows axial symmetry for 0.45 < x< 0.70 and orthorhombicsymmetry for x = 0.43. For x > 0.42, the crystallographic structure is cubic, and in absence of local disorder,a fully isotropic octahedral undistorted environment is expected for Cu. In the tetragonal structure, collectivemagnetic interactions arise, and a progressive EPR signal symmetrization is observed due to anisotropicexchange and to Dzialoshinsky−Moriya antisymmetric exchange processes. The mixing of triplet and singletstates induced by the above exchange mechanisms leads to the conclusion that the orbital order is melt in thex = 0.1 sample, for which the cooperative Jahn−Teller distortion is still active and the 3D magnetic order isstill antiferromagnetic, as in KCuF3.
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