Antiferromagnet, spin polarization

If the spin-polar on model is correct, we must describe the carriers in the antiferromagnetic semimetal formed when the two Hubbard bands overlap as a degenerate gas of spin polarons it should have the following properties. 

SAD Spin-alternant determinant. The VB determinant with one electron per site and with alternating spins. Other terms describing the same determinant are the quasiclassical (QC) state, and the antiferromagnetic (AF) state. In nonalternant hydrocarbons, where compete spin alternation is impossible, the determinant is called MS AD, namely, the maximum spin-alternating determinant. The SAD MSAD are the leading terms in the wave function of molecules with one electron per site, for example, conjugated hydrocarbons. In radicals (e.g., allyl radical) the SAD is the root cause of spin polarization (i.e., negative spin densities flanked by positive ones). See Chapters 7 and 8. 

In this paper, Section 2 will be devoted to describe spin-polarized first-principles calculational method, and Section 3 will examine the mechanism of the antiferromagnetic state. Section 4 will summarize the results. 

Fig. 22 Spin vortices and current generated by them [25]. (a) Two spin vortices embedded in the antiferromagnetic background. The spin polarization direction at j th site in the x-y plane is...

A 62-atoms embedded cluster in cubic geometry was considered to represent 7-Fe (see Fig. 17), and spin-polarized SCF calculations were performed for both the ferromagnetic (FM) and antiferromagnetic (AFM) states, at several lattice constants. For the AFM, a layered arrangement of up and down spins (illustrated in Fig. 17) was considered. 

Within the framework of the local density method, which is strictly an orbital theory, the antiferromagnetic state can be attained by reducing the symmetry constraints imposed on spin-polarized calculations, hence allowing the spin orbitals to localize and local magnetic moments to persist, if it is variationally favorable to do so. While I do not know of any formal justification for this type of symmetry breaking (one cannot just mix determinants within DFT to obtain proper spin and space eigenfunctions), the results discussed below for Cr2, M02, and Mn2 certainly indicate that it is a reasonable approach. A rough rationalization can be obtained if one reasons... 

Spin polarized, single-particle models can simulate antiferromagnetic systems at the expense of the sacrifice of spatial symmetry. This device is employed in generalizations of density functional theory but is often unsatisfactory for the... 

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