Spin polarization of excitons in organic multiferroic composites

Abstract

Recently, the discovery of room temperature magnetoelectricity in organic charge transfer complexes has reignited interest in the multiferroic field. The solution processed, large-area and low cost organic semiconductor materials offer new possibilities for the functional all organic multiferroic devices. Here we report the spin polarization of excitons and charge transfer states in organic charge transfer composites by using extended Su-Schrieffer-Heeger model including Coulomb interaction and spin-flip effect. With the consideration of spin polarization, we suggest a possible mechanism for the origin of excited ferromagnetism.

Organic Donor‐Acceptor Cocrystals for Multiferroic Applications

“…Moreover, due to the electron-phonon (chargelattice) coupling tightly related to the molecular assembly axes and spin cone orientation in CTC, this material exhibited anisotropic ferroelectricity, magnetization and ME coupling behavior (Figure 4). [30] Similar phenomena are also observed in the donor-acceptor segregated-stack CT cocrystals based on fullerene and other thiophene-based derivatives. [72,77] To be mentioned, a magnetoelastic character can also be realized in this polythiophene (P3HT) • C 60 system, where the saturation magnetization varies inversely with the applied static compression stress.…”

“…[19][20] The Ren group has done lots of explorations on the C 60 -based organic CT multiferroics. [29][30][31][32][33][34]77,82] A segregated-stack cocrystal with a long-range ordered CT network based on the electron donor TTF and acceptor C 60 was observed to display an unusual multitude of external stimulicontrolled ferroic properties, due to the modulation of chargespin composite orders (Figure 3a, b). [34] The density of singlet and triplet CT can be tuned by the magnetic field owing to the formation rate of spin-parallel and spin-antiparallel states for the competition of spin-conserving and spin-mixing.…”

“…[33] Another typical C 60 -based CT multiferroics system is the family of thiophene-based compounds, where thiophene acts as the electron-donating moiety. [29][30]32,72,77] For instance, by co- assembling thiophene donor and C acceptor together into athree-dimensional CTC with a hierarchical organization and long-range noncovalent interactions (segregated-stack), a remarkable anisotropic magnetization and room temperature multiferroicity can be achieved. [29] In this system, the ferromagnetism likely originates from the unpaired spin alignment within charged thiophene nanowires induced by the charge transfer.…”

“…However, some innovative and breakthrough researches have been obtained and significantly boosted the development of this field. [25,[27][28][29][30][31][32][33][34][35][36][37] Although many other systems such as polymers, [38a,b] covalent organic frameworks (COFs), [38c] or metal-organic frameworks (MOFs) [38d-f] have been demonstrated to show multiferroics properties, we only discuss recent progress in organic donor-acceptor cocrystals for multiferroic applications in this minireview. We begin with a brief description of multiferroics including the definition, history, evolution, significance, category and fundamental research to build a basic knowledge framework on the field, and then proceed with the presentation of the progress in experimental and theoretical investigations on organic CT multiferroics in the past decade.…”

Optically Controlled Magnetization and Magnetoelectric Effect in Organic Multiferroic Heterojunction

“…It should be noted that organic charge transfer complex does not have 3d electrons. Based on computational modeling, the origin of magnetism is resulted from electrons in organic acceptor to induce localized spin polarization . However, the other theoretical study showed that hole spins alignment in donor section will induce localized spin polarization, which is responsible for the origin of room temperature ferromagnetism .…”