Time dynamics of spins-fermional models in Cu2O

The solution of the system of equations for the basic operators of the spin-fermion model is obtained in the form of harmonic oscillations of Fermi operators at two frequencies, and three-frequency harmonic oscillations of the spin-fermion coupling operator (spin-polaron).

Аномальное изменение размера спинового полярона в парамагнитной области температур в La-=SUB=-1.2-=/SUB=-Sr-=SUB=-1.8-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

In this work, we continued the study of the magnetic and electrical properties of the double perovskite La1.2Sr1.8Mn2O7, which has a colossal magnetoresistance in excess of 1200 near the Curie temperature. It is shown that the colossal magnetoresistance observed in La1.2Sr1.8Mn2O7 is well described on the basis of the “orientational” and “spin-polaron” conduction mechanisms. It was found in the work that in the absence of a magnetic field, the linear size of the spin polaron decreases with increasing temperature in the ferromagnetic region, and upon the transition of manganite to the paramagnetic state, the linear size begins to increase, reaching a maximum at 180 K. At temperatures exceeding 180 K, an anomalous temperature change the size of the spin polaron disappears. In the absence of a magnetic field, the detected peak on the temperature curve of the change in the size of the spin polaron is maximal; with the inclusion of the magnetic field, the peak height decreases. Mechanisms are proposed to explain this anomalous temperature behavior of the spin polaron size.