Magnetic and transport properties of the magnetic polaron: Application to Eu1-xLaxB6 system

Abstract

To understand the role of the magnetic polaron in magnetic and transport properties of Eu1-xLaxB6, we investigate the low carrier density ferromagnetic Kondo lattice model by using the Monte Carlo methods. We demonstrate that the magnetic-polaronic ( MP) state with the insulating nature is realized in the phase-separated region in between the ferromagnetic and antiferromagnetic ( AFM) states in the phase diagram. The insulating behaviors of EuB6 just above T-C and of Eu1-xLaxB6 with 0.05 < x < 0.2 are well explained by MP states in the paramagnetic and the AFM background, respectively. The Eu vacancy plays a crucial role in forming the bound magnetic polaron and so producing the resistivity peak in EuB6. By applying the weak magnetic field, the AFM metallic ground state is destroyed into the MP state, but the metallic behavior is restored by the strong magnetic field, as is observed for Eu1-xLaxB6 with 0.2 < x < 0.3.