Structural Characterization and Evolution of the Electronic Behavior of New Sr2−xGdxMnTiO6 (0≤x≤1) Perovskites

Abstract

The structural and magnetic characterization of microcrystalline powders of new Ti manganites Sr2−xGdxMnTiO6 (0≤x≤ 1) are reported. Compositional characterization by means of thermogravimetric analysis, EDS, and XPS indicates the stoichiometry of all samples to be practically equal to the nominal one. A diminution in symmetry from cubic to orthorhombic has been detected as a function of x, being the critical composition x=0.75. Microstuctural aspects are deeply discussed from high‐resolution transmission electron microscopy data and they confirm that for x≤0.5 a cubic symmetry is adopted, whereas for x≥0.75 the samples become orthorhombic, with space group Pbnm. The complex magnetic response of the title materials is explained considering magnetic frustration derived from the presence of two magnetic sublattices (Gd and Mn), which could interact as a function of temperature and magnetic field. The existence of antiferromagnetic interactions is especially clear for low values of x, but even in these cases, hysteresis loops in the M versus H variation are obtained at 4.2 K. The global magnetic response can be understood taking into account weak ferromagnetic (FM) interactions at the Mn sublattice (Mn4+ and Mn3+ cations) together with the greater magnetic contribution of paramagnetic Gd sublattice at low temperature. No spin reversal behavior has been detected in any case. For the most doped samples, x=0.75 and 1, a predominant FM contribution of Gd sublattice seems to be operative.

Room temperature electroresistance in Sr2−xGdxMnTiO6 perovskites (0≤x≤1)

“…One can observe the existence of orthorhombic (pseudotetragonal) regions with different orientations on the nanometer scale. The structural analysis shows that the crystal structure gradually changes from cubic to orthorhombic as x → 1 [15]. This is in accordance with the increased number of Mn 3+ ions that suffer Jahn-Teller distortion.…”

“…The AF character of the x = 0 compound and its low-temperature FM transition indicate the strong competition between the FM and AF correlations. The T < 43 K ferromagnetism is incomplete (frustrated), as indicated by both the differences in ZFC and FC curves and their saturation moments M S [15]. Fig.…”

“…In between (0 < x < 1), a variety of states can be present, including both FM metallic and FM insulating state. The situation in Sr 2−x Gd x MnTiO 6 is similar: the magnetic ground state (low T) for all concentrations 0 < x < 1 appears to be a canted AF (or frustrated FM) state [15]. The introduction of gadolinium results in a partial change of valence of manganese ions (Mn 4+ → Mn 3+ ) and this leads to the drastic reduction of room temperature resistivity.…”

“…[15]. High resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) were performed using a PHILIPS CM200FEG super-twin, with point resolution of 0.24 nm ("C.A.I.…”

“…In the search for novel materials with a high dielectric constant, the double perovskite Sr 2 MnTiO 6 was synthesized in 2008 [13,14]. Additional promising properties can be achieved by a partial replacement of strontium with gadolinium: Sr 2−x Gd x MnTiO 6 [15]. The introduction of trivalent Gd ion leads to the partial change of manganese valence from Mn 4+ to Mn 3+ .…”