Description of the Colossal Magnetoresistance of La1.2Sr1.8Mn2O7 Based on Spin-Polaron and Orientation Conductivity Mechanisms in the Paramagnetic Temperature Region

Abstract

The resistance of single-crystal La1.2Sr1.8Mn2(1 – z)O7 is studied experimentally and theoretically in the 75–300 K temperature range in magnetic fields varying in intensity from 0 to 90 kOe. The magnetoresistance is governed by spin-polaron and orientation conductivity mechanisms. The observed magnetoresistance of La1.2Sr1.8Mn2O7 at 75–300 K is characterized using the method of separation of contributions from different conductivity mechanisms. The calculated and experimental data agree closely. Temperature dependences of the spin-polaron size (in relative units) are calculated in the 75–300 K interval in zero magnetic field and in a 90 kOe field. It is demonstrated that the increasing (along the magnetic field) spin-polaron linear size gives rise to colossal magnetoresistance. In other words, the size change of magnetic inhomogeneities produces the primary contribution to the colossal magnetoresistance value.