Incommensurate antiferromagnetics state

Below the Neel temperature, the beta phase is in an incommensurate helical antiferromagnetic state in which the helical turn angle varies from 24.0 at the Curie temperature to 42.9° at the Neel temperature (Greenhough et al., 1981). However, various turn angles are commensurate with the basal plane of the hexagonal crystal structure and nine such transitions have been definitely identified and the results are summarized in Part 14.13. Using sensitive calorimetry, Astrbm and Benediktsson (1988) were able to confirm only two of these transitions at 166 and 173 K and measured the enthalpies of transition to be 2 1 J/mol in both cases, but this is cmisidered to be within experimental noise and therefore these transitimis were not considered in the evaluation of the thermodynamic data. 

The beta phase below the Neel temperature at 180 K exists in an incommensurate helical antiferromagnetic state in which the helical turn angle varies from 24.0° at the Curie temperature to 42.9° at the Neel temperature (Green-hough et al., 1981). However, various turn angles are commensurate with the... 

The transformation at the Curie temperature involves the formation of an incommensurate helical antiferromagnetic state up to the lower Neel... 

Among invariants of fourth order, the invariant describing a temperature dependence of the antiferromagnetic order parameter is left only in (5). The invariants quadratic in the spatial derivatives of the order parameters are taken in the simple isotropic form. It will be shown below that the presence in Eq. (5) of other order parameters is not necessary for the evolution of the magnetic states in copper metaborate for temperatures decreasing from the paramagnetic phase above 20 K to the incommensurate phase below 10 K. 

As far as all selenium molecular compounds are concerned, the shallow minimum of the resistivity is no longer observed, but different behaviors are observed for the representative compounds (TMTSF)2PF6 and (TMTSF)2C104. The conductivity of the former compound reaches 106 (ft cm)-1 at 12 K and then vanishes abruptly as the system undergoes a metal-insulator transition [15] toward an antiferromagnetic (SDW) ground state, as indicated by NMR [53] and susceptibility measurements [54]. Furthermore, 13C NMR has proved the incommensurate nature of this SDW ground state [52]. It is the presence of this additional periodicity in... 

Fermi energy relative to the bottom of the CB). The Fermi level wave lengths are in general incommensurable with the crystal s interatomic or interplanar distances as a result, the magnetic ground states of the rare-earth intermetallics and pure metals have complicated spatial distributions, ferromagnetic, antiferromagnetic, helical, etc. 

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