Large effects ofA-site average cation size on the properties of the double perovskitesBa2−xSrx

Abstract

Ba 2Ϫx Sr x MnReO 6 (xϭ0, 0.5, 1, 2͒ phases with a double-perovskite structure were prepared by solid-state techniques in evacuated sealed silica tubes. Mn 2ϩ and Re 6ϩ are virtually completely ordered on the B sites. The compounds are ferrimagnetic below 120 K. The maximum saturation moment was obtained for a compound with xϭ0.5 whose tolerance factor is closest to 1. The whole series of compounds, 0.0рxр2.0, exhibits semiconducting behavior with variable-range hopping type of conduction. Sr 2 MnReO 6 has an unusually high coercive field ͑2.6 T at 5 K͒ and two transitions in the M -H loop. Ba 2 MnReO 6 shows large positive magnetoresistance ͑14% at 80 K, 5 T͒ below 140 K, while the other compositions studied exhibit negative magnetoresistance in the temperature range measured.

Evidence of unquenched Re orbital magnetic moment in AA′FeReO6 double perovskites

“…; BBЈ = FeMo, FeRe, CrRe, CrW, etc.͒ are being intensively studied in order to find a material with optimal performance. 2-7 Among them the Re-based double perovskites are the most promising compounds in terms of high Curie temperature, e.g., 538 and 635 K in Ca 2 FeReO 6 and Sr 2 CrReO 6 , respectively.3 Moreover, Re-based double perovskites are magnetically hard 4,6,8 and reveal large magnetoelastic effects, 9 which can only be explained by a substantial magnetocrystalline anisotropy due to the anisotropy of an unquenched orbital moment of Re. …”

“…3 Moreover, Re-based double perovskites are magnetically hard 4,6,8 and reveal large magnetoelastic effects, 9 which can only be explained by a substantial magnetocrystalline anisotropy due to the anisotropy of an unquenched orbital moment of Re. …”

Local Magnetic and Electronic Properties of the A2FeM'O6 (A = Ba, Sr, Ca, M' = Mo, Re) Double Perovskites

“…The white line feature at the Re L 3 edge is asymmetric, with a tiny bulge at around 3 eV below its maximum, which can be attributed to the splitting of the t 2g and e g final states [17]. We did not observe any difference in shape between the spectra of the compounds studied, which might be attributed to the lattice distortion.…”

“…The difference in their magnetic properties is especially intriguing. The Re-based double perovskites are magnetically hard [36,38,17] and reveal large magneto-elastic effects [40], which can only be explained by a large magnetocrystalline anisotropy due to anisotropy of not fully quenched orbital moment of Re [38]. This assumption is also supported by the results of recent self-consistent local spin density (LSDA) and generalised gradient approximation (GGA) calculations, which revealed a significant value of m L = 0.25 µ B per Re atom in Sr 2 FeReO 6 [30].…”

“…where r A is the average ionic radius of an ion at the A site, r M denotes the average ionic radius for the ions at the M, M sites and r O is the ionic radius of the O 2− ion (r O ≈ 1.40Å) [13][14][15][16][17]. A deviation of the tolerance factor from the ideal value f = 1 can be a measure of the structural mismatch caused by different ionic radii of the A and M, M cations.…”