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.

► Pure polycrystalline powders of Sr1−x□xLaMnTiO6−δ perovskites have been synthesized by the liquid mix technique.
► X-ray and neutron diffraction data, together with HRTEM are interpreted in terms of tetragonal symmetry and S.G. I4/mcm, being all the cations located at random in each sublattice.
► Magnetization measurements show the existence of a frustrated behaviour, implying FM interactions at low temperatures, and semiconductor behaviour is observed in the whole temperature range explored.
► The introduction of vacancies in the A sites is connected to the stabilization of the Griffiths phase for x < 0.15, and an electronic model considering a cluster glass picture is proposed.