Tuning magnetic critical behaviour in Ti-manganites by doping with vacancies in A-sites: Sr1−x□xLaMnTiO6−δ (0 < x ≤ 0.15)

Microcrystalline powders of Sr1−x□xLaMnTiO6−δ (0 ≤ x ≤ 0.15) perovskites have been synthesized by the sol–gel method. Structural characterization from neutron diffraction data shows tetragonal symmetry for all samples in the whole temperature range explored (5–700 K) and HRTEM analysis confirms it at the micro scale. Structural refinements suggest that Sr/La and Mn/Ti cations are placed at random in A and B sublattices, respectively, being the vacancies exclusively located on the former sites. Doping with vacancies in the A sites does not provoke any extra structural ordering or distortion but modifies the electronic scenario at the B-sites, leading to an enhancement of Griffiths phase as the amount of vacancies, x, increases. Semiconductor behaviour has been observed, without any transition to metallic state, with typical activation energies of 0.15 eV. The intrinsic magnetic frustrated behaviour is described in terms of a cluster-glass model.