AC susceptibility study of the bilayered cyano-bridged Cu-W and Cu-Mo ferromagnets

AC susceptibility, XAC, for ferromagnetic Cu-II[W-V(CN)(8)]- and Cu-II[Mo-V (CN)(8)]-based molecular magnets with TC approximate to 30 K of the unique bilayered structure is investigated. XAC (T) is measured with different frequency and amplitude of the oscillating field for various magnitudes of static applied field. Cu-II[W-V(CN)(8)]-based compounds show a sharp anomaly at the transition and extremely low effect below TC; second harmonic Of XAC and DC magnetization curves suggest some weak antiferromagnetic interactions while critical behaviour points to the Ising anisotropy in these samples. Susceptibility of these compounds is strongly enhanced by applying DC field of about 50 Oe. For the Cu-II[Mov (CN)(8)]-based compounds XAC is more typical and the critical exponent gamma is close to that of 3D Heisenberg magnets. It is suggested that the different behaviour of these isostructural and isospin compounds is related to the more diffuse 5d shell of tungsten centres that may enhance the possible anti ferromagnetic exchange through the CN-bridges. At HDC = 0 there is almost no frequency dependence Of XAC-Weak glass-like character of tungstate compounds which appears in the applied field is probably due to random weak interactions through the hydrogen bonds disordered in the space between the bilayers and random anisotropy coming from the countercations. (c) 2005 Elsevier SAS. All fights reserved.