Indirect exchange coupling

The compound Tl2Tc3 is a p-type semiconductor in which the thallium atoms are located in channels between puckered Te layers. A ° T1 and jvjmr study of this material has revealed that significant indirect exchange coupling occurs between the nuclei by overlap of the thallium electron wave functions, mainly across the Te atoms. Good agreement was found between the NMR conclusions and the calculated electronic stmcture and density of states in this semiconductor (Panich and Doert 2(XX)). 

Typically, is near to one for Ce systems with the bare f-level well below Ep. Note that the Anderson width A is much smaller than that conduction-band width, so that N (Ep) is indeed large when compared with the bare conduction-band DOS. On the other hand, it should be clear that singlet formation via an indirect exchange coupling cannot transfer much spectral weight from the bare local level up to Ep. Thus, a narrow resonance near the Fermi level of maximum height (jrAY and width k Tp < A arises. It should be emphasized that the local DOS considered here is not the quasiparticle DOS that is used in Fermi-liquid theory to express thermodynamic quantities via free-particle for-... 

Ruderman, M.A., Kittel, C. Indirect exchange coupling of nuclear magnetic moments by conduction electrons. Phys. Rev. 96, 99-102 (1954)... 

Since the indirect exchange coupling is between spins, Gd is distinguished by the highest Curie temperature (292.7 K) of the lanthanides as a result of its 4f ... 

We have thus obtained the expression of indirect exchange coupling between two magnetic ions. The sign of (132) depends on 2k Ri, because it is determined by the function... 

The canonical spin glass consists of a noble metal (Au, Ag, Cu, or Pt) diluted with a transition metal ion, such as Fe or Mn. The magnetic interaction in such systems is mediated by the conduction electrons, leading to an indirect exchange interaction—the RKKY (Ruderman and Kittel [70], Kasuya [71], and Yosida [72]) interaction, whose coupling constant J R) oscillates strongly with distance r between the spins as... 

Indirect exchange exchange coupling between electrons on centers that require the orbitals of an intermediate group or groups for the process to occur... 

Still, there is opposite-spin state left at each site. Hopping to one of the next-neighbor sites requires a spin flip. Therefore, metal-insulator transitions involve intersite magnetic exchange coupling. This is the second effect directly or indirectly involved in conductive properties of these crystals. Magnetic effects are briefly discussed in Sect. 4.2. 

Thus for spin 1=1/2 nuclei, the quantum mechanical exchange interaction is formally equivalent to an indirect spin-spin interaction. Accordingly the exchange of spin-1/2 particle is usually treated in NMR like a J-coupling (quantum exchange coupling), employing the more simple Hamiltonian... 

The effective hamiltonian representation of equations [8-10] is readily extensible to systems with more than one TM. The Hdd< matrix for such cases contains terms that account for d-electron delocalization (via the second term in Equation 9) from one metal to another - indirectly via the bridging ligands or directly via the corresponding off-diagonal terms of Hdd [33]. This interaction produces magnetic-exchange coupling, which is reviewed elsewhere [34, 35],... 

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