X-ray magnetic circular dichroism ͑XMCD͒ measured at T = 6 K and 0 H = 5 T on the ␣-phase Fephthalocyanine ͑FePc͒ textured thin films shows that the Fe 2+ ions present an unusually large, highly unquenched m L = 0.53Ϯ 0.04 B orbital component, with planar anisotropy. The spin m S = 0.64Ϯ 0.05 B and the intra-atomic magnetic dipolar m T components were also obtained. The m L / m S = 0.83 ratio is the largest measured in 3d complexes and compounds. The origin of this unusually high orbital moment is the incompletely filled e g level lying close to the Fermi energy. This explains the unusually large and positive hyperfine field detected by Mössbauer spectroscopy in FePc. The FePc film strong planar anisotropy inferred from XMCD experiments is fully confirmed by magnetization measurements.

A universal curve for the change in the magnetic entropy has been recently proposed for materials with second-order phase transitions. In this work we have studied the universal behavior of the magnetocaloric effect in the family of cobalt Laves phases, RCo 2 , and mixed manganites, La 2/3 ͑Ca x Sr ͑1−x͒ ͒ 1/3 MnO 3 , which exhibit first-and second-order phase transitions. The rescaled magnetic entropy change curves for different applied fields collapse onto a single curve for materials with second-order phase transition as opposed to the first-order phase transition compounds, for which this collapse does not hold. This result suggests that the universal curve may be used as a further criterion to distinguish the order of the phase transition.

The magnetic behavior of Fe 3Àx O 4 nanoparticles synthesized by either high-temperature decomposition of an organic iron precursor or low-temperature coprecipitation in aqueous conditions is compared. Transmission electron microscopy, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulklike magnetic and electronic properties, while nanoparticles synthesized by coprecipitation show much poorer crystallinity and particlelike phenomenology, including reduced magnetization, high closure fields, and shifted hysteresis loops. The key role of the crystal quality is thus suggested, because particlelike behavior for particles larger than about 5 nm is observed only when the particles are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or biodistribution studies. V