Abstract
Systematic studies on Pr 0.7 Sr 0.3-x Ca x MnO 3 , Pr 0.6 Sr 0.4-y Ca y MnO 3 , Pr 0.5 Sr 0.5 - z Ca z MnO 3 , and Cr-doped Pr 0.6 Sr 0.4 (Mn, Cr)O 3 reveal distinct origins of the magnetoresistance in Pr-based manganites. For Pr 0.7 Sr 0.3-x Ca x MnO 3 and Pr 0.6 Sr 0.4-y Ca y MnO 3 , the sharp enhancement of the magnetoresistance ratio (MR) around the ferromagnetic transition temperature (T c ) indicates a percolative field-induced transition. For Pr 0.5 Sr 0.5-z Ca z MnO 3 , the MR peak appears at the charge ordering temperature instead of T c , and the low-field MR shows a different behavior from those of Pr 0.7 Sr 0.3-x Ca x MnO 3 and Pr 0.6 Sr 0.4-y Ca y MnO 3 , suggesting that the relative population of ferromagnetic and antiferromagnetic domains governs the temperature dependent MR behavior. For Cr-doped Pr 0.6 Sr 0.4 (Mn, Cr)O 3 , the metal-insulator transition is shifted to a lower temperature with an enhancement of MR. Remarkably, it retains a weakly temperature-dependent character, which may be correlated with the spin scattering mechanism due to the presence of Cr-impurities. © 2002 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA.