Electron doping dependence of ferromagnetism in Eu1-xLaxB6

Abstract

The temperature dependent magnetization M(T) and electrical resistivity rho(T) were measured to study the electron doping effect in Eu1-xLaxB6 (x=0, 0.005, 0.03, 0.05, and 0.1). At room temperature, rho(T) decreases systematically with an increasing amount of electron doping. For a small doping with x=0, 0.005, and 0.03, M(T) exhibits ferromagnetic transitions and rho(T) reduces drastically below the transition, which also reveals characteristics of double transition. It is clearly found from both M(T) and rho(T) that the doped carriers in the region of x<0.03 lower the transition temperature. For the doping level with x=0.05, and 0.01, the ground-state properties look quite different from the ones of EuB6. While M(T) shows a ferromagneticlike behavior at low temperature, an increase of rho(T) around the ferromagneticlike region, rather than a reduction, is observed. This rho(T) behavior looks similar to the one in SmB6, which shows the opening of a Kondo insulating gap.