Antisite defects versus grain boundary competition in the tunneling magnetoresistance of the ${\mathrm{Sr}}_{2}\mathrm{Fe}\mathrm{Mo}{\mathrm{O}}_{6}$ double perovskite

Antisite defects versus grain boundary competition in the tunneling magnetoresistance of the ${Sr}_{2} Fe Mo O_{6}$ double perovskite

D. Niebieskikwiat, F. Prado, A. Caneiro, and R. D. Sánchez

Phys. Rev. B 70, 132412 – Published 29 October 2004

Abstract

We present magnetic and transport measurements on the ${Sr}_{2} Fe Mo O_{6}$ double perovskite, and study the tunneling magnetoresistance (TMR) response when the amount of $Fe ∕ Mo$ disorder (antisite defects) and the grain boundary (GB) properties are changed. We prepared two samples with different amounts of disorder (saturation magnetization $M_{S} \approx 3.0$ and $1.6 μ_{B}$ , respectively) and performed several GB oxidation treatments. While $M_{S}$ remained unchanged, the resistivity $(ρ)$ was increased by more than five orders of magnitude after oxidation and the TMR showed an appreciable increase, regardless of the amount of $Fe ∕ Mo$ disorder. At low $ρ$ values, the more disordered sample $(M_{S} \approx 1.6 μ_{B})$ shows a diminished TMR due to a reduced electron spin polarization. On the contrary, when the GBs dominate in the transport properties the effect of the disorder is washed away and both samples exhibit the same improved TMR values.