Ferromagnetism example molecules

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. 

As suggested earlier, high-spin molecules that have thousands of parallel spins would correspond to single domain particles of ferromagnetic substances. In a-iron, for example, a microcrystalline particle of radius 200 pm contains ca. 5000 spins and is considered to form a single domain structure. 

Beyond these two example applications a number of others have been described. These concern not only ordinary radicaloid (finite) molecules, but also polymer ends, graphitic comers, carbene containing systems (with ferromagnetic couplings between the singly-occupied a-orbitals and the 7t-network), and even some systems with transition metal centers involved in the exchange network. See Refs. [195,198]. 

Fdd2 fi form (Banister et al. 1996). The result is that in the a structure neighbouring chains are antiparallel, while in they are all parallel. Due to these symmetry considerations the a modification cannot exhibit a so-called spin-canting mechanism (Carlin 1989) which can account for the transition from a low-dimensional antifer-romagnet to a weakly ferromagnetic state. However, these restrictions are absent in the P modification, and this mechanism, based to a large extent on the structural distinction between the two polymorphs, has been used to account for the fact that this p form is the first example of an open-shell molecule to exhibit spontaneous magnetization above liquid helium temperature (36 K). 

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