Magnetic Phase Diagram of Layered La_2-2xCa_1+2xMn₂O₇

Abstract

Polycrystalline samples of the layered perovskite La_2-2xCa_1+2xMn₂O₇ with quasi-two-dimensional Mn-O networks were synthesized, and a magnetic phase diagram obtained. La_2-2xCa_1+2xMn₂O₇ has a two-type spin exchange interaction, one of which reflects the properties of the a-b plane, and the other properties of the c axis (out-of-plane) direction. As a result, for 0.22≤x≤0.5, there are three regions: PI (paramagnetic insulator), F1 (ferromagnetic insulator), and FM (ferromagnetic metal). We observed a giant magnetoresistance (GMR) of Δρ/ρ₀=64% (77 K, 1.8T, x=0.25), which is much larger than that reported for the three-dimensional perovskite La_1-xCa_xMnO₃. These results could be interpreted as due to anisotropic exchange interactions of La_2-2xCa₁+_2xMn₂O₇.