RFBR grant "Postgraduate students"
No. 20-32-90049
Theoretical study of spin effects in new magnetic heterocompounds
applications.
The aim of the presented project is the theoretical study of the atomic structure and features of spin conductivity in magnetic heterocompounds based on new low-dimensional materials that demonstrate such fundamental quantum physical phenomena as spin filtering, induced spin polarization, magnetoresistance effect. Modeling of heterostructures will be based on monolayers and thin films of various compounds (for example, metal nitrides, tellurides and carbides) with such key properties for spintronics as ferromagnetism, semimetallic band structure and surface magnetic anisotropy.
To achieve the goals of the project, the following tasks will be solved:
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Search and modeling of optimal magnetic heterocompounds based on semi-metallic ferromagnetic materials (electrodes) and non-magnetic intermediate layers that form the scattering zone.
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Study of the electronic, magnetic and transport properties of the proposed compounds in the framework of the theory of ballistic transport and NEGF formalism.
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Evaluation of the effectiveness and prospects for using the magnetic heterostructures under study as an element of a spin valve demonstrating a high level of spin polarization near the interface and high values of magnetoresistance.
As part of the project, a theoretical study of the structural, magnetic and electronic properties of new heterostructures based on various two-dimensional materials and the ferromagnetic semimetallic Heusler alloy CFGG was carried out:h-BN/CFGG, MoSe2/CFGG, MoS2/CFGG.
In all cases, the preservation of stable ferromagnetic properties of the CFGG substrate, including surface layers near the interface, was shown, which is due to the absence of strong chemical bonding of the surface with the monolayer. At the same time, a significant dependence of the surface electronic properties of CFGG on the type of surface termination was revealed. Thus, in the case of termination by Co atoms in the h-BN/CFGG heterostructure, the semimetallic properties of the substrate are retained and 100% spin polarization is observed already on the first CFGG atomic layer. On the contrary, in the case of termination by Fe/Ge/Ga atoms, spin-down electronic states arise at the Fermi level, which leads to the destruction of the semimetallic properties of CFGG. However, then the spin polarization quickly recovers, and starting from the fourth layer (~5 Å from the interface), its value exceeds 90%. Similar results were also obtained for MoSe2/CFGG, MoS2/CFGG, where for both terminations of the semimetal surface the spin polarization is rapidly restored within four to five layers. It is important to note that the distance at which the properties of the substrate are restored is much smaller than the characteristic spin diffusion length (~2 nm) in CFGG. This suggests that CFGG can be effectively used in spin valves even without interface termination control.
Finally, the tunnel magnetic heterostructure CFGG/MoS2/CFGG was proposed and theoretically studied for the first time within the framework of the project. The calculation of the spin-transport properties showed high values of the magnetoresistance coefficient of the order of 10^4–10^5%, depending on the number of MoS2 layers and the magnitude of the applied voltage. The obtained estimates significantly exceed similar values for TMG from other theoretical and experimental scientific works.
Thus, the presented results indicate a high prospect of using heterostructures based on two-dimensional materials and the semimetallic Heusler alloy CFGG in spintronics, including the creation of new high-performance spin valves.
Project participants
supervisor
d.ph.m.s., leading researcher Pavel Sorokin
NUST "MISIS"
executor
Konstantin Larionov
MIPT