Ferromagnetism prediction

With this assumption, and with 3.22 other orbitals available for occupancy by odd electrons or electron pairs, the ferromagnetic moment would be predicted to rise to a maximum of 3.22/u,B at Co and then to decrease steadily with slope -1 to 0 for the alloy Zn7gGa22- This prediction agrees only in part with observation the values of Pb for alloys Fe-Co, Co-Ni, and Ni-Cu (Fig. 1) reach a rounded-off maximum of about 2.50 and then decrease to 0 at... 

Fig. 1. Comparison of experimental values (solid curves) and predicted values (dashed lines) of the saturation ferromagnetic moment per atom, in Bohr magnetons, for Fe-Co, Co-Ni, and Ni-Cu alloys. The short vertical lines indicate change in crystal structure (from Ref. (2)).

In contrast, within (p-EPYNN)[Ni(dmit)2], first synthesized in 1996 [79], it has been proven that spin-ladder chains of the Ni(dmit)2 moiety coexist with the ferromagnetic one-dimensional chain of the p-EPYNN radical cation. Spin-ladders are of interest because of their potential applications in the area of quantum magnets and because it has been predicted that holes doped into even-leg ladders may pair and possibly superconduct [90-92]. 

These ideas have been tested by calculations on the ferromagnetic Ising model and the 10-state Potts model , where exact results on T, +, are available , and excellent agreement with the theoretical predictions Eqs. (45)-(50) was found. As an example. Fig. 10 shows the specific heat for finite 10-state Potts lattices and the scaling representation of these data resulting from Eq. (47). Also experimental data on rounded specific heats of O2 adsorbed on grafoil can be accounted by Eq. (47) quantitatively . 

It is relatively common for DFT calculations to not explicitly include electron spin, for the simple reason that this approximation makes calculations faster. In materials where spin effects may be important, however, it is crucial that spin is included. Fe, for example, is a metal that is well known for its magnetic properties. Figure 8.10 shows the energy of bulk Fe in the bcc crystal structure from calculations with no spin polarization and calculations with ferromagnetic spin ordering. The difference is striking electron spins lower the energy substantially and increase the predicted equilibrium lattice constant by 0.1 A. 

Isostructural compounds A2Crp4 have not been prepared yet. The same arguments as those above lead to the prediction of ferromagnetism within the MeF4 -sheets of octahedra, exactly as observed in fluorides ACrFa, but this time without the possibility of compensation by antiferromagnetic coupling between the layers. 

As discussed earlier, the original BCS theory predicted that superconductors were perfect diamagnets. It was therefore with surprise that solids were recently discovered that are both ferromagnetic and superconducting. 

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