Magnetic ordering and magnetoresistance of layered perovskite Nd1+xSr2-xMn2O7

Magnetic and transport properties of layered perovskite Nd1+xSr2-xMn2O7 cry stals have been studied. The material with x = 0 is insulating and antiferr omagnetic with spin-glass-like behavior at low temperature. On increasing x , the antiferromagnetic behavior is Suppressed and ferromagnetic behavior a ppears, and the resistivity decreases. The material with x = 0.2 shows two characteristic temperatures, T-c1 = 230 K and T-c2 = 80 K. Two-dimensional ferromagnetic correlation within c-plane appears below T-c1 and three-dimen sional ordering with easy-axis anisotropy is established below T-c2. The re sistivity increases steeply below T-c2 and a magnetic field of 7 T causes a colossal magnetoresistance of 97.5%. On further lowering the temperature, the anisotropic spin-glass state appears. These results are ascribed to the frustration of random competing double-exchange ferromagnetic and super-ex change antiferromagnetic interactions with the anisotropy originating from layered structure. (C) 2001 Elsevier Science B.V. All rights reserved.