Commensurate antiferromagnets

Fig. 39. The different magnetic structures of HoNi2 B2C as determined by neutron scattering, (a) Commensurate antiferromagnetic, (b) incommensurate restructure (spiral) with the modulation vector T2 = (0.0,0.916) and (c) proposal how the incommensurate a -structure looks like (Loewenhaupt et al. 1997). Its modulation vector is...

It is obvious that the commensurate antiferromagnetic structure of fig. 39a coexists with superconductivity in HoNi2B2C, similar as in DyNi2B2C. On the other hand, as can be seen in fig. 43(a and c) the superconductivity is suppressed in the small temperature range where the two incommensurate magnetic structures of fig. 39(b and c) occur. Now the question is which of these two structures is more relevant for the near-reentrant behaviour. In Y().i5Hoo.85Ni2B2C the situation is totally different (fig. 43(b and d)). Here the a ... 

Amici and Thalmeier (1998) used the quasi one-dimensional model mentioned in Section 4.9.1. In their approach the presence of ferromagnetically ordered Flo layers with the magnetic moments oriented perpendicular to the tetragonal c-axis is adopted and the competition of the RKKY interaction along the c-axis with the crystalline electric field is analyzed in order to determine the transition between the commensurate antiferromagnetic structure and the incommensurate c spiral shown in Figure 39. 

Figure 30 Phase diagram of (TMTCFljX proposed by Jerome [95]. PI, SP, C-AF, IC-SDW and SC represent paramagnetic insulating, spin-Peierls, commensurate antiferromagnetic, incommensurate spin density wave and superconducting phases, respectively. Tp denotes the temperature where the resistivity shows the minimum.

---