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Two examples of transition metal molybdates were studied with the use of X-ray diffraction and DC magnetometry techniques. First compound, copper dimolybdate trihydrate CuMo2O7∙3H2O contains 2D layers. The second one is fibrillar cobalt trimolybdate octahydrate CoMo3O10∙8H2O. Both compounds exhibit paramagnetic behaviour at room temperature. However, in the first one copper ions form dimers linked by oxygen bridges, in which exchange interactions between two localized spin states occur. The second compound consists of isolated cobalt ions in the octahedral surroundings, resulting in magnetic properties deviating from the Curie law. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic properties of copper dimolybdate trihydrate CuMo2O7·3H2O have been studied from room temperature down to 2K with the use of ac and dc magnetometry. There was no sign of long range order; however, the compound deviates from the classical Curie law for paramagnetic systems. This situation is due to exchange interactions between Cu ions forming dimers, whereas Mo ions do not possess magnetic moments. The estimated value of J ex is −2.74(1)K from fitting the dc susceptibility and −3.01(1) K from the fit of magnetization versus magnetic field. The antiferromagnetic coupling is confirmed by the value of θ=−4.0(3)K from the Curie–Weiss analysis. The dynamic properties measured by ac susceptibility as a function of applied dc field indicate three regions of different magnetic relaxation behaviors. [Copyright &y& Elsevier]