INFLUENCE OF A KONDO-HOLE IMPURITY BAND ON MAGNETIC INSTABILITIES IN KONDO INSULATORS

Kondo insulators like Ce3Bi4Pt3 and CeNiSn are compounds with small-ga p semiconductor properties. The Kondo insulator is described by the no ndegenerate symmetric Anderson lattice with, on average, two electrons per site within Kotliar and Ruckenstein's mean-field approximation in terms of four slave bosons per site. A Kondo hole is the charge neutr al substitution of a rare earth or actinide atom by a nonmagnetic anal og. An isolated Kondo hole gives rise to a bound state in the gap, whi ch pins the Fermi level and has magnetic properties. A finite concentr ation of Kondo holes generates an impurity band in the gap of the semi conductor. The low-temperature thermodynamic and transport properties are determined by the impunity band. The interplay of the f-electron c orrelations with the impurity band is studied in the paramagnetic phas e. On a bipartite lattice the pure Kondo insulator is unstable to long -range antiferromagnetism for U > U-c acid to ferromagnetism in suffic iently large magnetic fields. A small concentration of Kondo holes red uces the threshold for the antiferromagnetic transition, giving rise t o reentrance, but does not substantially affect ferromagnetism.