Conductivity and magnetic properties of TmSe and TmS: Comparison to the dilute cases

Magnetization, neutron diffraction, and resistivity measurements performed on the compounds TmSe and TmS are compared to those on the dilute alloys (Tm,Y)Se and (Tm,Y)S. In the paramagnetic regime, major differences exist between a regular array of Tm ions (TmSe and TmS) and the dilute systems. Localization (TmSe) or magnetic correlations (TmS) appear clearly in the conductivity behavior or in the dependence of the static susceptibility. A low content of Y atoms in TmSe has a drastic effect on the conductivity and on the magnetic order. We will discuss the connection between the degeneracy of the ground state with the opening of a gap.