P. M. Allemand

Organic molecular soft ferromagnetism in a fullerene C60

The properties of an organic molecular ferromagnet [C60TDAE0.86; TDAE is tetrakis(dimethylamino)ethylene] with a Curie temperature ;Tc = 16.1 kelvin are described. The ferromagnetic state shows no remanence, and the temperature dependence of the magnetization below ;Tc does not follow the behavior expected of a conventional ferromagnet. These results are interpreted as a reflection of a three-dimensional system leading to a soft ferromagnet.

On the complexities of short range ferromagnetic exchange in a nitronyl nitroxide

Abstract The molecular solid state structure and properties of 2-(4-nitrophenyl)-4,4,5,5-tetramethy-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide (1) were examined. The solid state structure of two ( α and β ) out of three phases, together with relevant short intermolecular contacts (to 3.60A) are presented. Solid state phase transformations, as detected by differential scanning calorimetry and electron spin resonance are described. As reported previously by Awaga, one phase of 1 exhibits short range intermolecular ferromagnetic interaction of the unpaired electrons. Explanation for the structural origin of this electron-electron interaction is hampered by the fact that 1 forms structurally completely different solid state phases, yet each phases shows qualitatively the same temperature dependance of the magnetic susceptibility but different electron spin resonance linewidths and linewidth behavior as a function of temperature.

Pressure dependence of magnetism in C60TDAE

Abstract We have determined the pressure response of magnetism in C60TDAE, where TDAE is tetrakis (dimethylamino) ethylene, and its temperature dependent susceptibility above and below the magnetic ordering temperature TC=16.1K. The magnetism is depressed very rapidly with applied pressure. We consider several possible interpretations for the magnetic transition and its pressure dependence and conclude that an itinerant-ferromagnet description is most likely.

Short range ferromagnetic exchange in 1,5,6-triphenyl-3-(4-nitrophenyl)-verdazyl

Abstract 1,5,6-Triphenyl-3-(4-nitrophenyl)-verdazyl has been synthesized and characterized by X-ray diffraction, magnetic susceptibility, ESR, and other spectroscopic methods, as well as elemental analysis. The product χ spin T was found to increase below 100 K to reach a maximum (0.529 emu.K/mole) at 3.9 K. From 100 to 30 K the spin susceptibility follows the Curie-Weiss law with C = 0.382 and Θ = +1.6 K, indicating ferromagnetic interactions between S = 1 2 species. A strong deviation from the Curie-Weiss law was observed below 30 K where the susceptibility reaches a maximum χ spin = 0.241 emu/mole at 2.15 K. Using the spin density rule proposed by McConnell, an attempt was made to correlate the unusual magnetic properties of this solid with its structure.

Mobile π Electrons From Donors and Acceptors

Abstract Concepts that evolved over the years for the design of organic metals and superconductors based on electron donor-acceptor charge transfer complexes are described. The preparation and complete characterization of three new acceptors; p-hexacyano divinylbenzene (HCDV), i-hexacyano divinylbenzene (i-HCDV) and 1,3,5-nonacyano trivinylbenzene (NCTV) are described. These were designed with different properties in mind. The latter for the preparation of organic ferromagnets based on the Breslow modification of the McConnell model.

Donors, acceptors and the FOM model

Abstract Electron donors and acceptors designed primarily for the formation of ferromagnetic organic metals (FOM) are described. The synthesis of molecules of trigonal symmetry which are either electron rich or electronegative as well as charge transfer complexes derived from them are described. The donor is a derivative of trimethylenemethane and the acceptor is 1,3,5-tris(tricyanovinyl)benzene.