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img Source of magnetic anisotropy in quasi-two-dimensional XY {Cu4(tetrenH5)W(CN)8]4·7.2H2O)}n bilayer molecular magnet  


O. Zaharko, M. Pregelj, A. Zorko, R. Podgajny, A. Gukasov, J. van Tol, S. I. Klokishner, S. Ostrovsky, and B. Delley

To identify the origin of the XY spin dimensionality in the bilayered system {Cu4(tetrenH5)[W(CN)8]4·7.2H2O}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.

http://dx.doi.org/10.1103/PhysRevB.87.02 ...

A. Menelle, 2013-06-21 00:00:00


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