Source of magnetic anisotropy in quasi-two-dimensional XY {Cu sub(4)(tetrenH sub(5))W(CN) sub(8)] sub(4) times 7.2H sub(2)O)}n bilayer molecular magnet

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2013-01, Vol.87 (2)
• Main Authors: Zaharko, O, Pregelj, M, Zorko, A, Podgajny, R, Gukasov, A, van Tol, J, Klokishner, S I, Ostrovsky, S, Delley, B
• Format: Article
• Language: English
• Subjects: Anisotropy; Copper; Crystals; Density; Exchange; Ion exchangers; Mathematical models; Origins
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.87.024406

To identify the origin of the XY spin dimensionality in the bilayered system {CU sub(4)(tetrenH sub(5))[W(CN) sub(8)] sub(4) times 7.2H sub(2)O}n (WCuT) we use a combination of single-crystal experiments (bulk magnetization, neutron flipping ratio, electron magnetic resonance, neutron diffraction) and theoretical modeling (exchange-charge model of the crystal field, dipolar energy, and density functional calculations). Our experiments show that the magnetic properties of WCuT are anisotropic and two-dimensional correlations build up below 70 K. The hard anisotropy axis is perpendicular to the layers (b axis) and a small anisotropy within the ac layers is present. Modeling of the crystal field validates treatment of tungsten and copper as spin S = 1/2 ions with anisotropic g values. The local magnetic anisotropy results from the common action of the crystal field and spin-orbit coupling and is along the c axis for both ions. Density functional calculations identify the origin of the ferromagnetic exchange in different energies and symmetries of the tungsten- and copper-dominated orbitals and anticipate different exchange couplings across the apical (along the b axis) and equatorial (in the ac plane) Cu-CN-W bridges due to difference in the hybridization efficiency. Calculation of the dipolar energy for various spin configurations suggests that dipolar interactions play a decisive role in the ac-planar anisotropy in this system. We propose that the effective XY spin dimensionality in WCuT is established by a combination of the axial local anisotropy of the W and Cu ions and the long-range magnetic dipolar interactions on the bilayered square lattice.