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Spin dynamics of the two magnetic molecular clusters Fe4 and Fe8, with four and eight Fe͑III͒ ions, respectively, was studied by means of Mössbauer spectroscopy. The transition probabilities W's between the spin states of the ground multiplet were obtained from the fitting of the spectra. For the Fe4 cluster we found that, in the range from 1.38 to 77 K, the trend of W's versus the temperature corresponds to an Orbach's process involving an excited state with energy of about 160 K. For the Fe8, which, due to the presence of a low-energy excited state, could not be studied at temperatures greater than 20 K, the trend of W's in the range from 4 to 18 K seems to correspond to a direct process. The correlation functions of the magnetization were then calculated in terms of the W's. They have an exponential trend for the Fe4 cluster, while a small oscillating component is also present for the Fe8 cluster. For the first of the clusters, vs T ( is the decay time of the magnetization͒ has a trend which, at low temperatures (TϽ15 K), corresponds to an Arrhenius law with a potential barrier of the order of the energy difference between the states ͉M ͉ϭ5 and M ϭ0 (Ϸ7 K). Instead, for TϾ15 K, follows the trend of W Ϫ1 . For the Fe8, follows an Arrhenius law, but with a prefactor which is smaller than the one obtained susceptibility measurements.

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Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for highenergy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mö ssbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mö ssbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites.