We report significant intergrain magnetoresistance (IMR) in polycrystalline double perovskites of at room temperature. Systematics of the temperature dependence of IMR indicates that the observed large room-temperature IMR in originates from the ferrimagnetic nature of insulating grain boundaries as well as the half-metallicity of this perovskite. Our results indicate that a new avenue for spin-polarized tunneling junctions is to utilize insulating interface layers with ferromagnetic or ferrimagnetic coupling.
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After the completion of our work, we have received a preprint by K.-I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, and Y. Tokura, Nature (London) 395, 677 (1998). The authors report the IMR effect in but their result is not as pronounced as ours (e.g., 10% at 4 K in 2 kOe, but our result is 22% at 8 K in 2 kOe).
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1999
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