Positive magnetoresistance of single-crystal bilayer manganites (La1−zNdz)1.4Sr1.6Mn2O7 (z = 0, 0.1)

Abstract

We investigate magnetoresistance, ρc, of single-crystal bilayer lanthanum manganites (La1−zNdz)1.4Sr1.6Mn2O7 (z = 0 and 0.1) 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 sample plane at the temperatures T < 60 K, along with the negative magnetoresistance typical of all the substituted lanthanum manganites. In the (La0.9Nd0.1)1.4Sr1.6Mn2O7 sample, the positive magnetoresistance effect is observed at temperatures of 60–80 K in an applied field parallel to the c axis. 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...