Electrical and magnetic properties of La2−xSrxNiO4: A tentative phase diagram

Abstract

La2−xSrxNiO4 shows a maximum in the c/a ratio around x=0.6 up to which composition the concentration of holes is equal to that expected theoretically. The material becomes a degenerate semiconductor above a certain temperature up to x=0.8, but is metallic at room temperature when x≥1.0. All the compositions with x≥0.05 are paramagnetic in the 15-300K range. Based on these measurements, an electronic phase diagram is tentatively proposed. It is noteworthy that the antiferromagnetic order disappears at low doping levels in both La2−xSrxNiO4 and La2−xSrxNiO4, but metallicity is seen at 300K only at a much higher x value in the former system.