Magnetic Ordering in a High‐Spin Donor–Acceptor Conjugated Polymer (Adv. Mater. 45/2022)

Large Room‐Temperature Magnetoresistance in a High‐Spin Donor–Acceptor Conjugated Polymer

“…Fitting the data to the Curie–Weiss law ( χ M = C/(T − θ) + χ 0 ) where C is the material‐dependent Curie constant, θ is the Weiss constant, and χ 0 accounts for any observable offset in the susceptibility gives a negligible value for θ , consistent with an amorphous, paramagnetic polymer film (Figure S1, Supporting Information). [ 29–32 ] The spin quantum number ( S ) was determined by measuring the magnetic moment as a function of the magnetic field at a fixed temperature and by fitting it to the paramagnetic Brillouin function in Equation () $$$$\begin{eqnarray}\frac{{\ M}}{{{M}_{\mathrm{s}}}} &&= \frac{{2S + 1}}{{2S}}\ coth\left( {\frac{{2S + 1}}{{2S}} \times \frac{{gS{\mu }_{\mathrm{B}}H}}{{{k}_{\mathrm{B}}T}}} \right) \nonumber\\ &&\quad-\; \frac{1}{{2S}}coth\left( {\frac{1}{{2S}} \times \frac{{gS{\mu }_{\mathrm{B}}H}}{{{k}_{\mathrm{B}}T}}} \right)\end{eqnarray}$$$$here H is the field in Oersted, T is the temperature, g is the g‐factor, k B is the Boltzmann constant, M S is the saturation magnetization, μ B is the Bohr magneton, and S is the spin quantum number fitting parameter. At 2.5 K, a fit to Equation () results in a value of S = 0.95, which is consistent with a high spin ( S = 1) ground state (Figure 1e inset).…”

“…The rapid removal of the solvent in spin‐coated thin films creates a uniform but largely amorphous polymer network in which the magnetic properties closely resemble powdered samples. [ 29 ]…”

“…[ 12,13 ] Common open‐shell OSCs include polycylic aromatic hydrocarbons, [ 14 ] quinoidal oligothiophenes, [ 15,16 ] donor–acceptor conjugated polymers (DA CPs), [ 17–22 ] non‐conjugated radical polymers, [ 23,24 ] and polyradicals. [ 25–27 ] In particular, DA CPs with narrow bandgaps and open‐shell diradical character are emerging materials that offer new opportunities for spin transport, organic magnetism, [ 28,29 ] and various (opto)electronic, spin‐based, and quantum functionalities not readily available from conventional closed‐shell OSCs. In closed‐shell materials, doping is required to obtain open‐shell character (i.e., unpaired electron spins) and to increase electrical conductivity; however, doped polymers are usually unstable, and their ionized nature leads to large structural and energetic disorders.…”

“…However, research on open‐shell and high‐spin DA CPs has largely focused on understanding the evolution of the ground‐state magnetic and electronic properties and establishing the role of spin‐spin interactions; thus, magnetic‐field effects on charge transport remain relatively unexplored. [ 17,21,29 ] Developing a fundamental understanding of how electronic and spin‐structure correlate with transport phenomena remains central to the development of a new generation of organic paramagnetic materials that can be applied in spin‐based device technologies.…”

Recent Progress of Organic Semiconductor Materials in Spintronics

“…The curie temperature of Pyrene‐F4TCNQ [41] charge transfer composite crystal is 305 K, and the saturation magnetization is 15.9 memu/g. The saturation magnetization of the copolymer based on benzodithiadiazole and thiophene synthesized by Steelman et al [42] . is close to 0.2 emu/g at 25 K. Organic charge transfer composites have attracted extensive attention in the field of semiconductors due to their good conductivity and excellent photoelectric conversion performance [43] .…”