Intergrain tunneling magnetoresistance in polycrystals of the ordered double perovskite<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">FeReO</mml:mi></mml:mrow><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Intergrain tunneling magnetoresistance (TMR) subsisting up to room temperature has been observed for polycrystalline ceramics of ${\mathrm{Sr}}_{2}{\mathrm{FeReO}}_{6},$ which has ordered double perovskite structure with Curie temperature above 400 K. The first-principles band calculation predicts that ${\mathrm{Sr}}_{2}{\mathrm{FeReO}}_{6}$ shows the half metallic ground state with the ferrimagnetic coupling of Fe and Re spins. The experimental results of electronic and magnetic properties are in accord with this picture. In fact, the magnitude of intergrain TMR with the magnetic field of 7 T at 4.2 and 300 K is as large as 21 and 7%, respectively, reflecting high spin polarization of carriers.

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