Magnetic and transport properties of amorphous Tb-Si alloys near the metal-insulator transition

The magnetic and transport properties of amorphous TbxSi1-x alloys for x near the metal-insulator transition (approximate to0.14) have been studied as a function of temperature, magnetic field, and composition. Local Tb magnetic moments act to localize extended-state carriers at low temperatures, similarly to Gd, causing a sharp drop in conductivity as a function of temperature. The spin-glass freezing seen in amorphous Gd-Si alloys is drastically affected by the randomly oriented local anisotropy of Tb; amorphous Tb-Si alloys show a broad poorly defined susceptibility peak and a strong frequency dependence which is not seen in amorphous Gd-Si alloys. The magnetic exchange interactions are strong but balanced ferromagnetic and antiferromagnetic, as in amorphous Gd-Si alloys, with little dependence on x and no effect of the metal-insulator transition. The Tb effective moment in the paramagnetic state shows similar effects to Gd: a peak at the metal-insulator transition due to polarization of carriers and suppression below the expected value far from it.