title: Melting of orbital ordering in KMgxCu1-xF3 solid solution.
abstract: The long-range and short-range structures of KMgxCu1-xF3 (0 < x < 1) have been investigated by means of XRPD 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 is induced by doping due to the different Cu and Mg environments. In fact, the EPR measurements have shown that the Cu environment is isotropic for x > 0.8. It shows axial symmetry for 0.45 < x < 0.70 and orthorhombic symmetry 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, collective magnetic interactions arise, and a progressive EPR signal symmetrization is observed due to anisotropic exchange and to Dzialoshinsky-Moriya antisymmetric exchange processes. The mixing of triplet and singlet states induced by the above exchange mechanisms leads to the conclusion that the orbital order is melt in the x = 0.1 sample, for which the cooperative Jahn-Teller distortion is still active and the 3D magnetic order is still antiferromagnetic, as in KCuF3.
authors.affiliation: Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, Milano, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Oliva
authors.forename: Marco
authors.initials: M
authors.lastname: Scavini
authors.forename: Serena
authors.initials: S
authors.lastname: Cappelli
authors.forename: Claudio
authors.initials: C
authors.lastname: Bottalo
authors.forename: Claudio
authors.initials: C
authors.lastname: Mazzoli
authors.forename: Paolo
authors.initials: P
authors.lastname: Ghigna