Tunneling conduction mechanisms in strontium ferromolybdate ceramics with strontium molybdate dielectric intergrain barriers

Magnetoresistance of Nanosized, Granular Sr2FeMoO6–δ–SrMoO4 Core–Shell Structures

“…Phenomenologically, we obtain a value of F % 14 by fitting of the resistivity in the absence of a magnetic field to data. [16] This value is reasonable because we have neglected disorder and charge scattering effects.…”

“…i.e., the samples possess a decreasing with temperature resistivity. [10][11][12][13][14][15][16] At T ( T 0 (large electrostatic energy), the conductivity is temperature independent and it corresponds to the expected formula for tunneling through a parabolic barrier. However, at high temperatures T ≫ T 0 (small electrostatic energy), the behavior becomes that of thermal activation.…”

“…On the contrary, the electric field enhancement at the junctions is expected to be in the order a factor M equal to the ratio of the average size of the conducting grains d to the average junction width w, M % d/w. Assuming for granular, nanosized SFMO-SMO core-shell structures d ¼ 75 nm and w ¼ 1.24 nm, [16] the resulting number nd/w will be still very large. In the resulting low-voltage regime and supposing direct tunneling through thin enough barriers, the sheet resistance up to a factor F is given by [24,26] R 0,sq:…”

“…In nanosized, granular SFMO-SMO core-shell structures, the barrier thickness is in the order of w % 1/χ. [16] On the contrary, the barrier is much thinner than the magnetic length l B ¼ (ħ/eB) 1/2 . In this case, the barrier height was experimentally found to follow the relation [28] V 0…”

“…Such samples consist of coldpressed SFMO, [10] doped cold-pressed SFMO, [11] sintered and granular SFMO, [12] grinded and sintered Sr 2 CrMoO 6 , [13] grinded and sintered as well as cold-pressed Sr 2 FeReO 6 , cold-pressed Sr 2 CrReO 6 and cold-pressed Sr 2 CrWO 6 , [14] Ba 2 FeMoO 6 thin films comprising crystalline grains with disordered grain boundary regions, [15] and nanosized, granular SFMO-SMO core-shell structures. [16] Each of the listed tunneling processes requires an adapted model. A phenomenological model to explain the magnetic field dependence of resistance in granular colossal MR materials was developed.…”