Anomalous Change in the Size of a Spin Polaron in the Paramagnetic Temperature Range in La1.2Sr1.8Mn2O7

This study continues investigation of the magnetic and electrical properties of double perovskite La1.2Sr1.8Mn2O7, which has a colossal magnetoresistance (above 1200) near the Curie temperature. It is shown that the colossal magnetoresistance observed in La1.2Sr1.8Mn2O7 is adequately described based on the “orientational” and “spin-polaron” conduction mechanisms. It is found that, in the absence of a magnetic field, the linear size of a spin polaron decreases with an increase in temperature in the ferromagnetic region, whereas during the transition of manganite to the paramagnetic state the linear size begins to increase, with a maximum at 180 K. At temperatures above 180 K, the anomalous temperature change in the size of a spin polaron disappears. In the absence of a magnetic field, the detected peak in the temperature dependence of the spin-polaron size is maximum; the peak height decreases after applying a magnetic field. Mechanisms are proposed to explain this anomalous temperature behavior of the spin-polaron size.