Antiferromagnetism and Anisotropy in the Susceptibility of YBa2Cu3Oy

Magnetic susceptibility was measured on grain-oriented YBa 2 Cu 3 O y (\(y{}6.1\) to 7.0). A distinct kink was observed in the susceptibility-vs-temperature curve at 435 K for \(y{}6.1\), when the external field was parallel to the c -axis. The kink is attributed to an antiferromagnetic transition and the magnetic susceptibility is well explained as a typical quadratic Heisenberg antiferromagnet with an exchange-interaction parameter of ∼950 cm -1 in the Cu(2) plane. The magnetic behavior changes gradually to the temperature-independent susceptibility of superconducting samples \((y{}7.0)\) with nearly constant parameters of anisotropy.