Ferromagnetism molecules

The dielectric permittivity as a function of frequency may show resonance behavior in the case of gas molecules as studied in microwave spectroscopy (25) or more likely relaxation phenomena in soUds associated with the dissipative processes of polarization of molecules, be they nonpolar, dipolar, etc. There are exceptional circumstances of ferromagnetic resonance, electron magnetic resonance, or nmr. In most microwave treatments, the power dissipation or absorption process is described phenomenologically by equation 5, whatever the detailed molecular processes. 

Finally, synthetic metals made of polymeric organic molecules may also show the property of ferromagnetism. Organic materials of this kind were first demonstrated in 1987 by Ovchinnikov and his co-workers at the Institute of Chemical Physics in Moscow. The polymer they used was based on a polydiacetylene backbone, which contains alternating double-single and triple-single bonds between the carbon atoms of the molecule (10.2). 

This highly conjugated molecule was stabilised with nitroxyl biradical side chains. The resulting material had sufficient ferromagnetism that a usable compass needle could be made from it. Despite the success of this demonstration, organic ferromagnetism remains a curiosity. Such polymers are not likely to replace conventional ferromagnetic metals in any application within the foreseeable future. 

In Science, every concept, question, conclusion, experimental result, method, theory or relationship is always open to reexamination. Molecules do exist Nevertheless, there are serious questions about precise definition. Some of these questions lie at the foundations of modem physics, and some involve states of aggregation or extreme conditions such as intense radiation fields or the region of the continuum. There are some molecular properties that are definable only within limits, for example, the geometrical stmcture of non-rigid molecules, properties consistent with the uncertainty principle, or those limited by the negleet of quantum-field, relativistic or other effects. And there are properties which depend specifically on a state of aggregation, such as superconductivity, ferroelectric (and anti), ferromagnetic (and anti), superfluidity, excitons. polarons, etc. Thus, any molecular definition may need to be extended in a more complex situation. 

G. A. Landrum, R. Dronskowki, The orbital origins of magnetism from atoms to molecules to ferromagnetic alloys. Angew. Chem. Int. Ed. 39 (2000) 1560. 

Concerning molecule-based magnets, the first spin-ladder was synthesized (/ -EPYNN)[Ni (dmit)2] (/ -EPYNN = / -7V-ethylpyridinium o-nitronyl nitroxide). Within the crystal lattice, the radical cation /7-EPYNN units are arranged in ID chains with ferromagnetic interactions. The chains of [Ni(dmit)2] moieties in the ladder formation exhibit coexistent antiferromagnetic interactions.1031,1032... 

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