Magnetism In Organic Materials Research Articles

МЕТАЛООРГАНІЧНІ МАГНЕТИКИ НА ОСНОВІ КОМПЛЕКСІВ ЗАЛІЗА З 1-НІТРОЗО-2-НАФТОЛОМ

Providing macroscopic magnetism in organic materials is a very complex but quite promising scientific problem. The need to create an organic magnet is due to a number of expected advantages, such as lightness, transparency, flexibility, ability to switch under the influence of light (magneto-optics), or chemical influences (sensors), creation of modern toners for digital printing, materials for chemical power sources etc. To understand the mechanism of biological processes, in particular, human thinking and DNA functioning may help to study the state of spin glass, biomagnetism, the mechanism of action of paramagnetic probes in living tissues and others. In the present paper the peculiarities of the structure and magnetic behavior of the iron complex with 1-nitroso-2-naphthol Na[Fe(C10H6(NO2)3] have been studied. The powder X-ray diffraction method determined that the crystal structure of the complex is monoclinic with the space group P2/1. According to cyclic voltammetry, the electrochemical behavior of the complex anion Fe(C10H6(NO2)3] is characteristic of reversible electrochemical systems with one electron transfer. Optical absorption bands are observed in the electronic spectra of the complex at 389, 690, and 763 nm. The dependences of the magnetic susceptibility of the complex on the temperature, frequency and magnetic field strength in the temperature range 1.5–200 K in the external magnetic field up to 90 kE and in the frequency range from 95 to 2000 Hz are obtained and analyzed. At low temperatures, the peculiarities of magnetic behavior characteristic of the state of spin glass are revealed. The EPR spectrum of the complex is a superposition of two lines, the behavior of which is opposite when the temperature changes in the range of 4–293 K, which indicates the unusual dynamics of the molecular surrounding the Fe3+ ion. Such features may be due to the presence of two structurally inhomogeneous magnetic centers that exhibit opposite spin dynamics with changing temperature. The presence of this dynamic can have a significant impact on the properties of the substance.

Magnetic behavior in metal-free radical thin films

<h2>Summary</h2> Magnetism in organic materials is very intriguing: the realization of long-range magnetic order in completely metal-free systems combines magnetic moments with useful properties of organic materials. An essential step for applications is the knowledge of the magnetic behavior that, so far, was investigated only in the proximity of light atoms to heavy metals, impurities, or vacancies, and not as an intrinsic property of thin films that are purely organic. Here, we unravel X-ray magnetic circular dichroism at the carbon and nitrogen K-edges in purely organic radical thin films. Our results show that, controlling the preparation, the magnetic behavior is different than in single crystals. Atomistic simulations indicate that the reason for this is the molecular arrangement in the films when compared with that in the single crystal. The tuning of the film magnetic properties by the molecular arrangement is an exciting perspective toward revealing new properties and applications.

Superconductivity and Magnetism in Organic Materials Studied with μSR

A review is given of the current status and recent progress in the use of μSR for the study of superconductivity and magnetism in organic materials. For organic superconductors, important factors are discussed that influence the observed μSR line widths and their field and temperature dependences in the superconducting state. The accumulated μSR results give direct information about the scaling relationship between superfluid stiffness and transition temperature that provides a strong constraint for theories of organic superconductors. For organic magnetism, μSR offers a sensitive probe for detecting various weak magnetic phenomena ranging from spin-density-wave transitions through spin dynamics and 3D ordering of Heisenberg chain systems to field induced magnetism of quantum spin liquids. Finally, experiments are described that focus on two current issues in organic spintronics: direct measurement of the spin coherence length and the identification of the relative importance of different mechanisms of sp...

Magnetism in organic materials

Neutral mono-, di- and tri-radical solids and radical cation salts were used to study the variation of intra- and inter-molecular exchange interaction with molecular packing and systematic molecular modifications. Cooperative magnetic behaviour related to localized manganese moments was characterized for manganese oxides as a composite in organic matrix or charge transfer salts of tetra-substituted porphinato manganese. Magnetic order was also observed in 1,3-dithienyl-5-phenyl-verdazyl electropolymerized with hexafluorophosphate as counterion.

Magnetism in organic materials

Tailoring magnetic interactions of organic solids is currently an area of intense research activity. We show that the quasi-one dimensional anti-ferromagnetic exchange coupling of the well-known organic free radical triphenylverdazyl (TPV) can be increased by a factor of 3 by systematic molecular modifications (i.e. J1d/kB = −16K for 1,3,5,6-tetraphenyl-verdazyl). 1,3,5-tri-6'-(1,3,5-triphenylverdazyl)-benzene as a representative of covalently bound multiradical molecules was analyzed as solid and in solution. The energetic spin-doublet-quartet separation and intermolecular exchange interaction were estimated. Cooperative magnetic behaviour with ordering temperature of about 40K and well-defined hysteresis loops (Hc(5 K) ≈ 40 Oe) has been achieved by the chelation of transition metals (e.g. Mn) in appropriate organic materials. NMR, ESR, static magnetic susceptibility, in part also a.c. susceptibility, specific heat and x-ray structural analysis were used to characterize these new organic magnetic materials.