Giant magnetoresistance of a two-dimensional ferromagnet La2−2<i>x</i>Ca1+2<i>x</i>Mn2O7

Abstract

Bulk samples of La2−2xCa1+2xMn2O7 with the layered Sr3Ti2O7-type perovskite structure have been successfully synthesized and investigated with respect to their magnetic and electrical properties. It is found that La2−2xCa1+2xMn2O7 (x=0.25) is a metallic ferromagnet with a magnetic transition temperature Tc of 215 K. The large magnetoresistance (MR) effect with Δρ/ρ0 of ∼60% at 1.8 T was observed in a wide temperature range below a cusp temperature in resistivity of 96 K, which is well below the magnetic Tc. This behavior is quite different from that of the well-known double-exchange ferromagnets such as La1−xCaxMnO3, where large MR effects are restricted to a narrow temperature range around the ferromagnetic transition. The present result could be interpreted by using the double-exchange theory incorporating the anisotropy resulting from the two-dimensional Mn-O-Mn networks in La2−2xCa1+2xMn2O7.