Anisotropic low-field magnetoresistance of polycrystalline manganite sensors

Magnetic-field sensors of bulk La0.67Sr0.33MnO3 and La0.67Ba0.33MnO3 were f abricated. The investigations show that a large low-field magnetoresistance (MR) is exhibited by the polycrystalline samples. MR ratios of the sensors as large as 20% at 77 K and 1.5% at 298 K were observed in fields of 700 O e. Corresponding field sensitivities as high as 170%/T at 3 mT and 298 K, a nd 700%-960%/T at 3-8 mT and 77 K were obtained. The low-field MR is associ ated with intergranular transport of spin-polarized electrons. It is found to be highly anisotropic. The phenomenon is discussed in terms of spin-pola rized transport through two kinds of grain boundaries. These represent two extremes of grain-boundary environments. (C) 1999 American Institute of Phy sics. [S0003-6951(99)04017-6].