Antiferromagnetic Ordering and Paramagnetic Behavior of Ferromagnetic Cu6 and Cu18 Clusters in BaCuO2+x

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Science  15 Apr 1994:
Vol. 264, Issue 5157, pp. 402-404
DOI: 10.1126/science.264.5157.402


Magnetization and neutron diffraction measurements on polycrystalline BaCuO2+x revealed a combination of magnetic behaviors. The Cu6 ring clusters and Cu18 sphere clusters in this compound had ferromagnetic ground states with large spins 3 and 9, respectively. The Cu6 rings ordered antiferromagnetically below the Néel temperature TN = 15 ± 0.5 kelvin, whereas the Cu18 spheres remained paramagnetic down to 2 kelvin. The ordered moment below TN was 0.89(5) Bohr magnetons per Cu in the Cu6 rings, demonstrating that quantum fluctuation effects are small in these atomic clusters. The Cu18 clusters are predicted to exhibit ferromagnetic intercluster order below about 1 kelvin.