Intergranular Magnetoresistance inSr2FeMoO6from a Magnetic Tunnel Barrier Mechanism across Grain Boundaries

Abstract

We present magnetization (M) and magnetoresistance (MR) data for a series of Sr2FeMoO6 samples with independent control on antisite defect and grain-boundary densities, which reveal several unexpected features, including a novel switching-like behavior of MR with M. These, in conjunction with model calculations, establish that the MR in Sr2FeMoO6 is dominantly controlled by a new mechanism, derived from the magnetic polarization of grain-boundary regions acting like spin valves, leading to behavior qualitatively different from that usually encountered in tunneling MR. We show that a simple and useful experimental signature for the presence of this spin-valve-type MR (SVMR) is a wider hysteresis in MR compared to that in M.

A half-metallic A- and B-site-ordered quadruple perovskite oxide CaCu3Fe2Re2O12 with large magnetization and a high transition temperature

“…7b). The behaviour is similar to that observed in halfmetallic Sr 2 FeMoO 6 and suggests a spin-valve-type magnetoresistance due to the intergrain tunnelling of spin-polarized conduction carriers 54 Crystal structure analysis. A SXRD experiment was carried out for phase identification and crystal structure analysis.…”

Origin of the unconventional magnetoresistance in Sr 2 FeMoO 6

“…The synthesis of ordered cold-pressed pellets of Sr 2 FeMoO 6 have been discussed previously 9,11,12 . The excellent degree of phase purity and B-site Fe/Mo ordering (∼90%) were confirmed in a Bruker AXS: D8 Advance x-ray diffractometer, while the magnetic and magnetotransport measurements were carried out in a Cryogenics PPMS as well as in a Quantum…”

“…However, drastic exceptions have recently been observed [8][9][10] in a family of double perovskite TMR materials [11][12][13][14] , especially in their cold pressed form 9,10 , where H c[M R] has been found to be several times larger than H c [M ] . This highly anomalous observation was rationalized, for the representative case of Sr 2 FeMoO 6 (SFMO), on the basis of a hypothesis that the insulating barriers between the soft ferromagnetic, metallic grains are composed of relatively hard magnetic material and the phenomenon was termed as SVMR 9 .…”

“…This highly anomalous observation was rationalized, for the representative case of Sr 2 FeMoO 6 (SFMO), on the basis of a hypothesis that the insulating barriers between the soft ferromagnetic, metallic grains are composed of relatively hard magnetic material and the phenomenon was termed as SVMR 9 . Surprisingly, there has been no attempt to test the above mentioned hypothesis so far, in spite of its obvious importance to validate a new class of MR materials, possessing an unusual switching behavior.…”

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

“…The magneto-resistive behaviour of (BaSr) 2 FeMoO 6 [6] was explained in terms of tunnelling between two correlated spin glass-like surfaces separated by a thin insulating layer. The magnetization and magneto-resistance (MR) data for a series of SFMO samples [7] were interpreted in terms of a model in which the grain-boundary regions act as spin valves; this MR was termed SVMR. It was shown [8] that SVMR is a generic feature of the metallic, ferromagnetic doubleperovskite family as a whole.…”