4f magnetism

The second is the breakthrough in understanding complex 4f magnetism through the applications of some advanced magnetic measurements and quantum chemistry calculation methods, such as the single-crystal magnetic measurement... 

In the case of the Y-Ba-Cu-0 system, 4f magnetic ions may not be considered to be impurities as far as the superconductivity is concerned. As many investigators have discovered(18-24), most of the rare earth elements give 90 K superconductors without any appreciable difference in Tc. Kishio et al. (25) have shown that 90 K conductors can be also successfully prepared even from certain compositions of unseparated mixture of rare earths as starting materials. 

Liu (1961) noted that the wave functions of the 4f electrons on different rare earth (R) atoms in the solid state do not usually overlap. This is because the radius of the 4f shell is almost 0.35 A and the wave functions are therefore zero on the Wigner-Seitz sphere. There can therefore be no direct exchange, and exchange interactions between different R-magnetic moments must be mediated by the conduction electrons. Liu points out that there are two possible interaction types. In the first type the 4f magnetic moment on the R-atom polarizes the sp conduction bands of the compound via a direct s-f exchange interaction given by... 

Other RAI2 intermetallics with R=Pr, Nd, Gd, Dy, Ho, Er and Tm (see table 6) were first studied by Chappert et al. (1981) and Hartmann et al. (1984, 1986) with the aim to investigate fluctuations of 4f magnetic moments in the paramagnetic regime, especially on approach to the Curie point. The TF method was used exclusively. The main features of this study were ... 

Fig. 8. Comparison between R 4f magnetic moments (open squares) and Fe K-edge integrated XMCD signal (diamonds) for RjFei B compounds (Matu-yama 1998).

GdFei2 does not exist as a stable compoimd but electronic structure calculations using the LMTO-ASA method by Trygg et al. (1992) have been performed. As was observed in the experiment on the RMn systems there is a pronoimced influence of localized 4f magnetism on the conduction-band magnetism (transition-metal sublattice) which gives noticeable changes in the local moment of the iron (transition element). The presence of the 4f spin moment is found to induce a redistribution of the spin moment between the rare-earth and iron sites, while the total conduction-electron moment remains constant. It seems that these conclusions have also some importance for the ternary materials. 

Fig. 30. Paramagnetic form factors of CePds at 4.2 and 100 K plotted versus sin OjX = QI4n. The solid line has been obtained by fitting the 100 K data to the 4f magnetic form factor of Ce. The dashed line was obtained assuming an 83% 4f-17% 5d distribution of the induced moment (Stassis et al. 1982).

The second term, H-z, is the Zeeman coupling between the 4f magnetic mo-... 

Thus the presence of the 4f spin moment induces a redistribution of the spin moment between the lanthanide and M sites, while the total conduction electron moment remains constant. This cancellation between the two 4f-induced extra spin moments also occurs to a large extent for non-saturated magnetism, and explains the successful interpretation of experimental magnetic moment data in terms of a constant conduction electron spin moment and an atomic 4f magnetic moment for a series of compounds. 

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