Correlation of the magnetic and magnetotransport properties in a Nd1.5Sr1.5Mn2O7 single crystal

A detailed study of the anisotropic magnetic and magnetotransport behavior has been performed on a single crystal of the layered perovskite Nd1.5Sr1.5Mn2O7 The magnetic properties are consistent with an antiferromagnetic (AFM) ordering below T-N = 190 K of the manganese moments within the ab plane and a moment reorientation around approximate to 125 K towards the c direction. A spin-glass behavior develops for T < 50 K attributed to the freezing of the magnetic moment of the Nd(1) ions placed within the perovskite blocks, whereas the Nd(2) ions in the rocksalt layer contribute to the observed AFM order. An additional ferromagnetic contribution is observed below 275 K, ascribed to the existence of intergrowths. Low-field magnetoresistance (MR) is observed for H parallel to c in both rho(c) and rho(ab), reaching values up to 30% at T = 10 K. It is associated with the reduction of the spin disorder of the Mn moments aligned parallel to the c axis. For higher-field values the sharp decrease in MR is correlated with the magnetic "flipping" transitions. Within the whole temperature range the magnetoresistence is anisotropic, depending on both the direction of the applied field and current. Evidence is provided against the existence of spin-polarized tunneling between the layers in this compound. [S0163-1829(99)03232-4].