Molecular magnetic materials are the subjects of active research in recent years because of their possible applications in future information processing and storing devices. Inorganic molecular magnetic materials with spins on metal ions and the exchange pathway provided by the organic radicals that do not contain spins have drawn a special attention. The most important compounds in this category belong to Prussian Blue family having general formula CyAn[B(CN)6]m.x(H2O) where A and B being the transition or rare earth metal ions and C is monovalant cation. We are particularly interested in Prussian Blue analogues, Ax[Fe(CN)6]y×zH2O. In these hexacyanoferrates magnetic properties can be tuned by incorporating different transition metal cations at A site. We have prepared polycrystalline samples of Fe4[Fe(CN)6]3.yH2O, KNiII[FeIII(CN)6].yH2O, FeIII[FeIII(CN)6].yH2O, {FexIINi(1-x)II}1.5 [FeIII(CN)6].yH2O (x=0 – 1.0) and {CoxIINi(1-x)II}1.5[FeIII(CN)6].yH2O (x = 0 – 1.0) using the precipitation method. Detailed structural and magnetic properties of some of these molecular magnetic materials have been studied using x-ray diffraction, dc magnetization, neutron diffraction, Mossbauer spectroscopy and IR spectroscopy techniques. Rietveld refinement technique has been applied in order to obtain various structural parameters. Single-phase formation, with space group Fm3m, for all the samples is confirmed. Detailed DC magnetization measurements and low temperature neutron diffraction measurements have given the nature of magnetic ordering in these hexacyanoferrates. The valance state of Fe and its site symmetry have been obtained from Mossbauer study. For example our study confirms that in Fe[Fe(CN)6].4H2O, Fe3+(0, 0, 0) is in high spin state and Fe3+(1/2, 1/2, 1/2) is in low spin state, as predicted by the ligand-field theory. A net moment of 5.2 mB per formula unit was derived from the observed site moments. Observed ferromagnetism in the present system is viewed under the framework of molecular-field theory. My talk will cover the recent results from our study on these hexacyanoferrates [1-3]. [1] A. Kumar, S.M. Yusuf and L. Keller, Phys. Rev B 71 (2005). [2] A. Kumar and S.M. Yusuf, Pramana- J. Phys. 63, 239 (2004). [3] S. M. Yusuf et al. (unpublished).
Solid State Physics Division, Bhabha Atomic Research Centre