Magnetic Poly(ionic liquid)s: Bottlebrush versus Linear Structures

Spin Glass Transition of Magnetic Ionic Liquids Induced by Self-Assembly

Spin glass (SG), in which the spins are glassy, has attracted broad attention for theoretical study and prospective application. SG states are generally related to disordered or frustrated spin systems, which are usually observed in inorganic magnets. Herein, supramolecular magnetic ionic liquid (TMTBDI[FeCl4]) self-assemblies are prepared by solution self-assembly via hydrophobic and π-π stacking interactions. The supramolecular self-assemblies are in short-range lattice ordering and long-range disordering structures, as the lattice self-assemblies with the tens of nanometer scale are distributed randomly to form a long-range disorder. The shortest Fe(III)-Fe(III) distance is calculated to be ca. 2.4 Å from transmission electron microscopy (TEM) results. The magnetic properties of the supramolecular self-assemblies are studied via direct current (DC) and alternating current (AC) magnetic susceptibility characterizations. It is noted that TMTBDI[FeCl4] is paramagnetic before self-assembly. However, the supramolecular self-assemblies exhibit a strong ferromagnetic interaction due to the short Fe(III)-Fe(III) distance. The AC results show that the supramolecular self-assemblies are in the SG state at low temperatures as the imaginary part of the susceptibility moves to high temperatures with frequency. The self-assembly-induced spin glass transition of TMTBDI[FeCl4] is due to the long-range disordering and short-range ordering structures of the self-assemblies, which induces a frustrated spin system.

Ho-Ion-Polymer/Graphene Heterojunctions Toward Room-Temperature Ferromagnets

Organic ferromagnetic materials offer great promise for spintronic devices, carbon-based chips, and quantum communications, but remain as a challenging issue due to their low saturation magnetization and/or unsustainable ferromagnetic properties. To date, magnetic ion polymers have displayed paramagnetism without exception at room-temperature. In this study, it is reported for the first time that, owing to the structural restriction and charge exchange of Ho ion by polymer/graphene π-π stacking heterojunctions, holmium ion polymer composites exhibited typical hysteresis lines of ferromagnetic materials at room temperature. The room-temperature ferromagnetic ion polymer composite presented the highest saturation magnetization value of 3.36 emu g^-1 and unprecedented sustainable ferromagnetism, compared to reported room-temperature organic ferromagnetic materials. Accordingly, prepared ferromagnetic composites also achieved impressive wave absorption properties, with a maximum reflection loss of as much as -57.32 dB and a broad absorption bandwidth of 5.05 GHz. These findings may promote the development of room-temperature organic ferromagnetic materials.

Self-Assembly of a C16M[Mn] Magnetic Surfactant in Water

A magnetic surfactant, which combines the properties of a surfactant with magnetic responsiveness, shows great potential in biotechnology, separation, adsorption, and catalysis, especially in non-invasive manipulation through a magnetic field. However, a molecularly magnetic surfactant is usually paramagnetic for the amorphous and less ordered structures. In this work, magnetic surfactant 1-methyl-3-hexadecane-imidazolium [MnCl₂Br] (C₁₆M[Mn]) is reported to self-assemble in water. The C₁₆M[Mn] magnetic surfactant self-assembles in water to form a lamellar hydrogel from 10 to 50 wt % at and below room temperature. The hydrogel changes from a gel to a sol at 30 °C, and the hexadecane chains in the hydrogel change from noncrystalline to crystalline at 0 °C. In the hydrogel state, the lamellar domain spacing is varied from 36 to 45 nm depending on the concentration and self-assembly temperature. After self-assembly, the magnetic susceptibility of the freeze-dried magnetic surfactant is increased. Most important is the fact that the freeze-dried sample at a high concentration (40-50 wt %) shows the highest magnetic susceptibility, which is related to the closer molecular packing and the more ordered structures. The self-assembly-induced increase in magnetic susceptibility provides a method for improving the magnetic properties of a magnetic surfactant.