Features Of Magnetoresistance In The Bilayer Single Crystal Manganite LA1.4SR1.6MN2O7

We investigate magnetoresistance of single-crystal bilayer lanthanum manganite La1.4Sr1.6Mn2O7 at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La1.4Sr1.6Mn2O7 manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab plane of the sample at the temperatures T < 60 K. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic structure of the investigated compounds.