Limits...
Giant multiferroic effects in topological GeTe-Sb 2 Te 3 superlattices

View Article: PubMed Central - PubMed

ABSTRACT

Multiferroics, materials in which both magnetic and electric fields can induce each other, resulting in a magnetoelectric response, have been attracting increasing attention, although the induced magnetic susceptibility and dielectric constant are usually small and have typically been reported for low temperatures. The magnetoelectric response usually depends on d-electrons of transition metals. Here we report that in [(GeTe)2(Sb2Te3)l]m superlattice films (where l and m are integers) with topological phase transition, strong magnetoelectric response may be induced at temperatures above room temperature when the external fields are applied normal to the film surface. By ab initio computer simulations, it is revealed that the multiferroic properties are induced due to the breaking of spatial inversion symmetry when the p-electrons of Ge atoms change their bonding geometry from octahedral to tetrahedral. Finally, we demonstrate the existence in such structures of spin memory, which paves the way for a future hybrid device combining nonvolatile phase-change memory and magnetic spin memory.

No MeSH data available.


The upper panel shows the RESET and SET models and the corresponding bulk band structures, and HAADF TEM images of the [(GeTe)2/(Sb2Te3)1]20 iPCM (∼40 nm thick) grown on Si(111).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC5036496&req=5

Figure 2: The upper panel shows the RESET and SET models and the corresponding bulk band structures, and HAADF TEM images of the [(GeTe)2/(Sb2Te3)1]20 iPCM (∼40 nm thick) grown on Si(111).

Mentions: The structures of the SET and RESET states are shown in the upper panel of figure 2 together with the corresponding band structures. One can see that the RESET phase has a Dirac-like density of states. This fact, combined with the calculated topological invariant Z2 = 1, suggests that the RESET state is a strong topological insulator protected by spatial inversion and time reversal symmetries [19]. The SET phase, on the other hand, has a gap due to the breaking of spatial inversion symmetry, resulting in spin-split band structures. The differences between the two phases were clearly observed using high-angle annular dark field transmission electron microscopy (HAADF-TEM), as shown in figure 2. (See the supplementary material for details.) It is noted that the obtained HAADF-TEM images of real iPCM films are in good agreement with the results of earlier simulated models for the SET and RESET states [18, 19]. When one Ge layer is swapped with the adjacent Te layer by an external stimulus such as temperature or electric field, the RESET state transforms into the SET state and vice versa [18]. The change of the electric dipole moment (dielectric constant) induced by the phase transition generates large optical and electrical contrast [9].


Giant multiferroic effects in topological GeTe-Sb 2 Te 3 superlattices
The upper panel shows the RESET and SET models and the corresponding bulk band structures, and HAADF TEM images of the [(GeTe)2/(Sb2Te3)1]20 iPCM (∼40 nm thick) grown on Si(111).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036496&req=5

Figure 2: The upper panel shows the RESET and SET models and the corresponding bulk band structures, and HAADF TEM images of the [(GeTe)2/(Sb2Te3)1]20 iPCM (∼40 nm thick) grown on Si(111).
Mentions: The structures of the SET and RESET states are shown in the upper panel of figure 2 together with the corresponding band structures. One can see that the RESET phase has a Dirac-like density of states. This fact, combined with the calculated topological invariant Z2 = 1, suggests that the RESET state is a strong topological insulator protected by spatial inversion and time reversal symmetries [19]. The SET phase, on the other hand, has a gap due to the breaking of spatial inversion symmetry, resulting in spin-split band structures. The differences between the two phases were clearly observed using high-angle annular dark field transmission electron microscopy (HAADF-TEM), as shown in figure 2. (See the supplementary material for details.) It is noted that the obtained HAADF-TEM images of real iPCM films are in good agreement with the results of earlier simulated models for the SET and RESET states [18, 19]. When one Ge layer is swapped with the adjacent Te layer by an external stimulus such as temperature or electric field, the RESET state transforms into the SET state and vice versa [18]. The change of the electric dipole moment (dielectric constant) induced by the phase transition generates large optical and electrical contrast [9].

View Article: PubMed Central - PubMed

ABSTRACT

Multiferroics, materials in which both magnetic and electric fields can induce each other, resulting in a magnetoelectric response, have been attracting increasing attention, although the induced magnetic susceptibility and dielectric constant are usually small and have typically been reported for low temperatures. The magnetoelectric response usually depends on d-electrons of transition metals. Here we report that in [(GeTe)2(Sb2Te3)l]m superlattice films (where l and m are integers) with topological phase transition, strong magnetoelectric response may be induced at temperatures above room temperature when the external fields are applied normal to the film surface. By ab initio computer simulations, it is revealed that the multiferroic properties are induced due to the breaking of spatial inversion symmetry when the p-electrons of Ge atoms change their bonding geometry from octahedral to tetrahedral. Finally, we demonstrate the existence in such structures of spin memory, which paves the way for a future hybrid device combining nonvolatile phase-change memory and magnetic spin memory.

No MeSH data available.