ChemInform Abstract: Synthesis, Structural Characterization and Magnetic Properties of the Monoclinic Ordered Double Perovskites BaLaMSbO₆, with M: Mn, Co and Ni.

Abstract

in air (alumina crucible, 1. 780 C, 12 h, 2. 900 C, 10 h, 3. 1250 C (for Ni and Co perovskites) and 1350 C for Mn perovskites, 24 h). (I) and (III) belong to the monoclinic space group I2/m, while (II) crystallizes in the tetragonal space group I4/m. (II) and (III) show the expected 3D-antiferromagnetic behavior typical for super-superexchange interactions, while (I) displays signs of superparamagnetism in the 40-160 K range which is attributed to unbalanced antiferromagnetism inside nanoclusters formed by regions rich in Mn 2+ -O 2--Mn 2+ paths. Neutron powder diffraction data for (I) reveal that long range order antiferromagnetic arrangement of Mn 2+ spins on 2d octahedral sites occurs only at 3 K. -(BLANCO, M. C.; DE PAOLI, J. M.; CEPPI, S.; TIRAO, G.; NASSIF, V. M.; GUIMPEL, J.; CARBONIO*, R. E.; J. Alloys Compd. 606 (2014) 139-148, http://dx.doi.org/10.1016/j.jallcom.2014.04.013 ; Dep. Fis. Quim., Fac. Cienc. Quim., Univ. Nac. Cordoba, 5016 Cordoba, Argent.; Eng.) -J. Schramke 31-008

Chemical Substitution-Induced and Competitive Formation of 6H and 3C Perovskite Structures in Ba3–xSrxZnSb2O9: The Coexistence of Two Perovskites in 0.3 ≤ x ≤ 1.0

“…This might also be the reason why the M−O−M angles always deviate from 180°in many Sb 5+ -containing double perovskites (i.e., La(Ba/Sr)MSbO 6 (M = Zn 2+ , Mn 2+ ). 13,36,41 And it could also explain the quick descending rate of the symmetry from Fm3̅ m to I2/m in 3C-type Ba 3−x Sr x ZnSb 2 O 9 (1.3 ≤ x ≤ 3.0), even though the tolerance factor exhibited only a minor decease (see Figure 6). Of course, there existed some exceptional but rare cases exhibiting the 180°Sb−O−Sb connection, that is, Ba 4 LiSb 3 O 12 and Ba 4 NaSb 3 O 12 .…”

“…34 Considering the group−subgroup relationship and the extinction condition of the XRD patterns, we found the most probable space group in our case was I2/m, although it was rarely seen; for instance, only a few Sb 5+ -based perovskites LaBaMSbO 6 (M = Mn 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) possess this space group. 13,32,35,36 According to the above analyses on powder XRD patterns for Ba 3−x Sr x ZnSb 2 O 9 (1.3 ≤ x ≤ 3), Sr 2+ -doping-induced and successive symmetry lowering was observed from Fm3̅ m to I4/ m and then to I2/m. The same symmetry-lowering sequence has been observed in Ba 2−x Sr x InTaO 6 , 37 Ba 2−x Sr x YIrO 6 , 38 and A 2 CoWO 6 (A = Ba 2+ , Sr 2+ ).…”

Signs of superparamagnetic cluster formation in LuFe1−xCrxO3 perovskites evidenced by magnetization reversal and Monte Carlo simulations

“…This is reasonable since an inhomogeneous solid solution would present Fe 3+ -or Cr 3+ -rich regions and a tendency to form magnetic nanoclusters. The formation of magnetic nanoclusters has been overwhelmingly informed in literature [33][34][35][36][37][38][39][40]. The thermal protocol being the same, the rate of heating and cooling should not affect the formation of clusters, if any, which would imply that the different heat treatments and processing of the sample is responsible for the differences in magnetic behavior.…”

“…Moreover, cluster formation in perovskite solid solutions or double perovskites has been explored recently to describe different experimentally observed magnetic phenomena [35][36][37][38]. For example, superparamagnetism in double perovskite Ba 1+x La 1−x MnSbO 6 with 0.1 x 0.7 can be explained by the formation of three-dimensional nanoclusters formed by regions rich in Mn 2+ − O 2− − Mn 2+ superexchange paths [39,40]. In addition, recent studies show that MR in La 1−x/2 Bi x/2 Fe 0.5 Cr 0.5 O 3 perovskites is due to canted WFM domains and clusters richer in chromium or iron AFM coupled through Cr 3+ − O − Fe 3+ interactions [41].…”

Effect of B-Site Order–Disorder in the Structure and Magnetism of the New Perovskite Family La2MnB′O6 with B′ = Ti, Zr, and Hf

“…To double-validate the oxidation state of Mn obtained from the analysis of NPD data, we decided to perform highresolution Kβ emission measurements in one member of the family, the Zr-based compound, because it has the highest oxidation state value of Mn obtained through NPD. For this reason, high-resolution Kβ emission spectra of La 2 MnZrO 6 were measured together with those for mixed manganese oxides (MnO, Mn 2 O 3 , and MnO 2 ) and the double perovskite BaLaMnSbO 6 , 28 whose oxidation states are known and therefore could be used as standards (further details are presented in the Supporting Information, Figure S4a−c). From this analysis, it was obtained that the average oxidation state of Mn in the perovskite La 0.99(1) Mn 0.52(1) Zr 0.48(1) O 3.00 is (2.10 ± 0.11), which is in very good agreement with the value obtained from the analysis of NPD data.…”