Finding Universal Correlations between Cationic Disorder and Low Field Magnetoresistance in FeMo Double Perovskite Series

Abstract

We search for general patterns that explain the low field magnetoresistance at low temperatures in the system A(2-x)A'xFeMoO6. The observed linear dependence of the low field magnetoresistance with the saturation magnetization for the series is related to the antisite disorder at the Fe and Mo sites. This is explained in terms of a spin dependent crossing of intragranular barriers originated from the presence of antiferromagnetic SrFeO3 patches that naturally develop when antisite disorder occurs in the double perovskite. The presence of a moderate level of antisite disorder is at the very root of low field magnetoresistance although effects such as disorder distribution, connectivity, or morphology add their contribution.

Epitaxial growth and transport properties of Sr2CrWO6 thin films

“…The saturation magnetization M S was found to strongly depend on the growth conditions and the substrate material. A maximum value of M S = 1.9 µ B /f.u at 5 K was obtained for a 48 nm thick film grown on (111) SrTiO 3 [7] or Argon atmosphere [5,8,16] in a temperature range between 700 and 900 • C. Under these conditions (e.g. T = 800 • C, p O 2 = 1 × 10 −8 Torr) the surface of the SrTiO 3 substrates becomes oxygen deficient within a few minutes.…”

“…On these substrates a much rougher surface and a more distorted crystal structure is obtained. This is caused by the larger lattice mismatch of these substrates to Sr 2 CrWO 6 as compared to SrTiO 3 .…”

“…T C = 635 K in Sr 2 CrReO 6 [2]. Large low field magnetoresistance effects are found in Sr 2 FeMoO 6 [1,3], Sr 2 FeReO 6 [4] and Sr 2 CrWO 6 [5]. Thin films of the well studied system Sr 2 FeMoO 6 have been fabricated by pulsed-laser deposition (PLD) at relatively high temperatures of about 900 • C [6].…”

“…Here, we report on the epitaxial growth of Sr 2 CrWO 6 . Due to the good lattice match, epitaxial films of this material can be grown on SrTiO 3 substrates in a molecular layer-by-layer growth mode resulting in high crystalline quality. Sr 2 CrWO 6 thin films were deposited from stoichiometric targets [5] on atomically flat, HF etched and annealed (001) SrTiO 3 substrates by PLD using a 248 nm KrF excimer laser [9].…”

Direct Observation of Cationic Ordering in Double Perovskite Sr2FeReO6 Crystals

“…These oxides present antisite~AS! defects, in which cationic ordering in B-sites is frustrated by the occupation of B cations of B ' sites and vice versa; this situation is known to remarkably degrade the magnetic saturation, as well as the magnetoresistance~Balcells et al, 2001;García-Hernádez et al, 2001;Navarro et al, 2001!. So far, the conventional way to determine the presence of cationic ordering such as AS defects is to utilize a statistical tool~Lindén et al, 2000; Nakamura & Oikawa, 2003;Zajac et al, 2007! such as neutron diffraction, X-ray diffraction~XRD!, and Mossbauer spectroscopy, but the atomicscale observation of the local distribution of Fe/Re disordering cannot be predicted by such macroscopic analytical tools, even though the atomic-scale defective structures, such as antiphase boundary~APB!…”