Two-dimensional antiferromagnetic correlation with spin [formula omitted] in magnetic susceptibility of (La, Sr) 2NiO 4

Abstract

Measurements of the magnetic susceptibility χ of nonsuperconducting (La 1−χSr χ) 2NiO 4 (LSNO) with χ close to 0.5 between 5 and 700 K revealed the presence of a broad peak in the temperature dependence of χ as observed in superconducting (La 1−χSr χ) 2CuO 4 (LSCO). The broad peak is attributed to the two-dimensional antiferromagnetic (2DAF) correlation between S = 1 2 spins of Ni 3+ in the low-spin state. However, contrary to LSCO, the peak temperature, T max, which is related to the correlation energy J, increases with χ for LSNO. In LSNO e g electrons are distributed to the 3d x 2− y 2 and 3d z 2 orbitals, both of which are not completely occupied. A strong 2DAF correlation exists among Ni 3+ spins in a (3d x 2− y 2) 1 configuration. With increasing χ, the fraction of Ni 3+ ions in the (3d x 2− y 2) 1 configuration increases and the effective J increases. This overlap of the orbital levels appears to play an important role in the absence of superconductivity in LSNO.