RKKY long range

The polarization of the conduction band due to the Hamiltonian of eq. (19) oscillates spatially with a long-range damping factor. The polarized conduction electrons can now scatter magnetically with another R atom. The resultant exchange interaction is known as the RKKY interaction and accounts for most of the magnetic properties of RI compounds. 

It is widely accepted that the moment coupling in rare earth alloys proceeds by means of the long-range RKKY mechanism involving a spatial non-uniform conduction electron polarization. The coupling constant of eq. (25) then takes the form (De Gennes, 1962a,b) ... 

In the present section, we review the properties of the stoichiometric Ce compounds exhibiting competition between heavy-fermion superconductivity and long-range magnetic order. We shall not discuss the highly complex phase diagrams obtained in alloy systems. In addition, we summarize recent attempts at a theoretical description of the complex low-frequency dynamics resulting from the competition between Kondo effect and RKKY interaction. 

The materials are all metallic (except possibly for some of the nitrides) and possess the NaCl structure. The exchange interaction between the lanthanide ions is thus probably of the RKKY type and involves oscillatory long range... 

The incompletely filled 4f-shell confers a magnetic moment to the lanthanide ions and it is the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism via polarization of the conduction electrons which is responsible for the occurrence of long-range ordered magnetic structures in the lanthanide metals. Details can be foimd in numerous reviews, among others in vol. 1, chs. 3, 6 and 7 (1978) of this Handbook series and a recent one by Jensen and Mackintosh (1991). The addition of hydrogen, both in solution or resulting in hydride formation, leads to a decrease of the conduction electron density e (cf. sect. 5)... 

In metallic systems with 4f atoms the most prominent source of long-range interaction between magnetic moments is the mechanism first described by Ruderman and Kittel (1954), Kasuya (1956) and Yosida (1957), which involves the conduction-electron sea as mediator of the interaction. Distinctive features of the RKKY-interactions are its long range and oscillatory nature ... 

For a lattice of nearly localized Ce or U impurities in which / is small, the application of pressure should enhance RKKY interactions and consequently 7 n. However, for sufficiently high pressure, or equivalently large l l, Kondo compensation of the local moments should dominate RKKY interactions and suppress the development of long-range magnetic order. This intuitive conclusion, which follows simply from considering that 7 n depends geometrically on y whereas 7 k varies exponentially, is supported... 

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