title: Antiferromagnetic Ordering and Paramagnetic Behavior of Ferromagnetic Cu6 and Cu18 Clusters in BaCuO2+x.
abstract: Magnetization and neutron diffraction measurements on polycrystalline BaCuO2+x revealed a combination of magnetic behaviors. The Cu(6) ring clusters and Cu(18) sphere clusters in this compound had ferromagnetic ground states with large spins 3 and 9, respectively. The Cu(6) rings ordered antiferromagnetically below the Néel temperature T(N) = 15 +/- 0.5 kelvin, whereas the Cu(18) spheres remained paramagnetic down to 2 kelvin. The ordered moment below T(N) was 0.89(5) Bohr magnetons per Cu in the Cu(6) rings, demonstrating that quantum fluctuation effects are small in these atomic clusters. The Cu(18) clusters are predicted to exhibit ferromagnetic intercluster order below about 1 kelvin.
authors.forename: Z R
authors.initials: ZR
authors.lastname: Wang
authors.forename: X L
authors.initials: XL
authors.lastname: Wang
authors.forename: J A
authors.initials: JA
authors.lastname: Fernandez-Baca
authors.forename: D C
authors.initials: DC
authors.lastname: Johnston
authors.forename: D
authors.initials: D
authors.lastname: Vaknin