2-DIMENSIONAL ANTIFERROMAGNETIC CORRELATION WITH SPIN 1/2 IN MAGNETIC-SUSCEPTIBILITY OF (LA, SR)2NIO4

Measurements of the magnetic susceptibility chi of nonsuperconducting (La(1-x)Sr(x))2NiO4 (LSNO) with chi close to 0.5 between 5 and 700 K revealed the presence of a broad peak in the temperature dependence of chi as observed in superconducting (La(1-x)Sr(x))2CuO4 (LSCO). The broad peak is attributed to the two-dimensional antiferromagnetic (2DAF) correlation between S = 1/2 spins of Ni3+ in the low-spin state. However, contrary to LSCO, the peak temperature, T(max), which is related to the correlation energy J, increases with x for LSNO. In LSNO e(g) electrons are distributed to the 3d(x2-y2) and 3d(z2) orbitals, both of which are not completely occupied. A strong 2DAF correlation exists among Ni3+ spins in a (3d(x2-y2)1 configuration. With increasing x, the fraction of Ni3+ ions in the (3d(x2-y2)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.