Giant magnetoresistance and extraordinary magnetoresistance in inhomogeneous semiconducting RENiBi compounds

Some inhomogeneous semiconducting C1b compounds RENiBi (RE=Gd,Dy,Er) show a negative giant magnetoresistance (GMR) above the magnetic ordering temperature in the paramagnetic temperature regime. Except for a weak deviation, this magnetoresistance scales roughly with the square of the magnetization in the paramagnetic state, and is related to the metal-insulator transition. At low temperature, a positive magnetoresistance is found, which can be suppressed by high magnetic fields. The nonmagnetic inhomogeneous semiconducting compound LuNiBi shows a large postive MR ratio of 25% at room temperature. The positive MR may be due to metallic bismuth impurities in the sample that cause an extraordinary magnetoresistance (EMR)