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Spin-dependent transport of electrons in an external magnetic field

Magnetic structure of Sr2FeMoO6-δ

The total spin S=2 consist of spins S(Fe3+) = 5/2 and S(Mo5+) = -1/2. Eectronic spins Fe3+ and Mo5+ are placed in Fe/Mo ferrimagnetic plates, which are intercrossed at the angle 120o. Due to the non-parallel arrangement of spins in the crystal lattice a ferrimagnetic structure is formed.



In SFMO the 3d5 electron shells of Fe3+ are fully occupied with spin-up e↑ electrons. These electrons are located below the Fermi level and thus they do not participate in the exchange interaction. On the contrary, the spin-down t2g↓ electrons of Mo5+ cations, which are located within the conduction band at the Fermi level, are mobile. In this case, the mechanism of exchange interaction is realized by a double exchange of t2g electrons. They are located at the hybridized Fe(t2g↓) and Mo(t2g↓) orbitals of the Fe3+ – O2-Mo5+ chain group. This half-metallic nature of the electron states provides a nearly 100% spin polarization in SFMO.


The magnetoresistance of films Sr2FeMoO6-δ

The magnetoresistance value in the SFMO film is expressed by the equation TMR = [ρ↑↓ - ρ↑↑]/ρ↑↑= 2P1P2/[1 - P1P2]. It is caused both by the spin polarization degree and by the number of magnetic domains with a different orientation of magnetization vector.

In this case one should consider the SFMO film as a domain system containing alternating magnetic and non-magnetic domains, and having various spin disorder, which in its turn lowers with the temperature decrease.



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