Magnetism, heavy electron systems

In this short review we have given examples of chemically induced changes in the behaviour of heavy-electron materials. First we noticed that the mere occurrence of the heavy-electron state seems almost unpredictable if only the chemical composition and the crystal structure of a compound are given. Then we pointed out that the heavy-electron state itself is quite sensitive to small alterations of the chemical composition in the sense that it can be destroyed or created by minor variations of the constituents of respective materials. Finally we emphasized that possible ground states of heavy-electron systems, like superconductivity or magnetic order, may be... 

As their name implies, strongly correlated electron systems encompass materials whose dominant physical properties are determined by the presence of strong correlations in their electronic structure, in particular between the open shell (magnetic) electrons and the charge carriers in the conduction band. The most prominent members are the high Tc superconductors and the heavy-fermion (HF) compoimds. The former have already been discussed in sect. 7, the latter are the subject of this section. 

The determination of the y-values is important for the classification of YbTX intermetallics as heavy-fermion systems which exhibit significantly enlarged y-values. The source of the large y-values arises from the compensation of the magnetic moment associated with a nearly localized electron state, generally of f character, by the spins of the conduction electrons in the metallic material. 

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