Origin of the unconventional magnetoresistance in Sr ₂ FeMoO ₆

Abstract

The unusual magnetoresistance (M R) behavior in Sr 2 FeMoO 6 , recently termed as spin-valve type MR (SVMR), presents several anomalies that are little understood so far. The difficulty in probing the origin of this phenomenon, arising from the magnetic property of only a small volume fraction of the ferromagnetic bulk, is circumvented in the present study by the use of ac susceptibility measurements that are sensitive to the slope rather than the magnitude of the magnetization. The present study unravels a spin-glass (SG) like surface layer around each soft ferromagnetic (FM) grain of Sr 2 FeMoO 6 . It is also observed that there is a very strong exchange coupling between the two, generating 'exchange bias' effect, which consequently creates the 'valve', responsible for the unusual M R effects.

Magnetoresistance and electroresistance effects in Fe3O4nanoparticle system

“…This is demonstrated in a plot of H C versus H MR C in Figure 3(c). Therefore, the homogeneous magnetite system behaves as a conventional TMR system and not as the recently reported spin-valve-type MR (SVMR) systems [22][23][24]. The observed MR% (inset of Figure 3b) values are in accordance with the previously reported values [25,26] for the Fe 3 O 4 bulk and the nanoparticle system [19,27] showing that the prepared nanoparticles retain the full spin polarisation without any surface oxidation effects.…”

Effect of ex situ Post-annealing Treatments on Sr2FeMoO6 Thin Films

“…For as-deposited film magnetoresistivity measurements show up to 6% negative MR at 10 K and for vacuum annealed film slightly smaller. Similar MR values for SFMO thin films have been reported in [10] and slightly larger values for polycrystalline sample in [26]. Results for as-deposited film show no hysteretic behavior at any temperatures and hysteresis is observed at 350 K for the vacuum annealed film as seen in Fig.…”

Inter-grain tunnelling in the half-metallic double-perovskites Sr2BB'O6(BB'= FeMo, FeRe, CrMo, CrW, CrRe)

“…It was shown [8] that SVMR is a generic feature of the metallic, ferromagnetic doubleperovskite family as a whole. Careful ac susceptibility measurements on a highly ordered polycrystalline sample of SFMO [9] were able to separate the barrier layer signal from the bulk. The presence of an intrinsic insulating boundary layer, about 2 unit cells thick, around grains of (LaSr)MnO 3 with magnetic properties different from those of the bulk [10], is held responsible for the depressed magneto-transport properties in manganite based magnetic junctions.…”

“…Unlike the difficulty in separating the magnetic properties of the layers from those of the bulk [9], it is relatively easy to study the electronic properties of the grain skin layers when the electronic transport is dominated by inter-grain tunnelling as is the case in most of the polycrystalline samples of the title materials. In this report we focus on the zero-field conductivity of various samples of the five title compounds using results accumulated in this lab.…”