We report a direct observation of the intrinsic magnetization behavior of Au in thiol-capped gold nanoparticles with permanent magnetism at room temperature. Two element specific techniques have been used for this purpose: X-ray magnetic circular dichroism on the L edges of the Au and 197Au Mössbauer spectroscopy. Besides, we show that silver and copper nanoparticles synthesized by the same chemical procedure also present room-temperature permanent magnetism. The observed permanent magnetism at room temperature in Ag and Cu dodecanethiol-capped nanoparticles proves that the physical mechanisms associated to this magnetization process can be extended to more elements, opening the way to new and still not-discovered applications and to new possibilities to research basic questions of magnetism.

Different samples of the sodium-vanadium fluorophosphate cathodic materials have been synthesized via the hydrothermal method, varying the type and content of carbon used in the synthesis. Structural characterization of the composites was performed by powder X-ray diffraction. Magnetic susceptibility measurements and EPR (Electron Paramagnetic Resonance) polycrystalline spectra indicate that some of the samples exhibit V 3+ /V 4+ mixed valence, with the general formula Na 3 V 2 O 2x (PO 4 ) 2 F 3À2x where 0 # x < 1. The morphology of the materials was analyzed by Transmission Electron Microscopy (TEM). A correlation between the type and content of carbon with the electrochemical behavior of the different samples was established. Electrochemical measurements conducted using Swagelok-type cells showed two voltage plateaux at 3.6 and 4.1 V vs. Na/Na + . The best performing sample, which comprised a moderate percentage of electrochemical grade carbon as additive, exhibited specific capacity values of about 100 mA h g À1 at 1C (z80% of theoretical specific capacity). Cyclability tests at 1C proved good reversibility of the material that maintained 98% of initial specific capacity for 30 cycles.

Compounds with the general formula [MM‘(C3H2O4)2(H2O)4] (M = Ba, Sr; M‘ = Cu, Mn; C3H2O4 = malonate) have been synthesized and characterized. Single-crystal X-ray diffraction study on the [SrCu(C3H2O4)2(H2O)4] compound indicates that it crystallizes in the orthorhombic space group, Pccn, Z = 4, with unit cell parameters a = 6.719(2), b = 18.513(7), and c = 9.266(4) Å. The structure consists of distorted octahedral copper(II) species which are extended along the ac plane forming a two-dimensional structure. The geometry of the alkaline-earth ions resembles a distorted antiprism. The other compounds are isostructural. The EPR spectra of the [MCu(C3H2O4)2(H2O)4] (M = Ba, Sr) compounds show an orthorhombic g tensor as consequence of a linear combination of the axial symmetry and the exchange interactions between magnetically different centers, but crystallographically equivalent. For the manganese compounds, the EPR spectra of polycrystalline samples show that the intensity of the signal increases with decreasing temperature down to 20 K, and at lower temperatures the intensity decreases, becoming silent below 7 K. Magnetic measurements show two-dimensional (2D) ferromagnetic and antiferromagnetic interactions for the copper and manganese phases, respectively. In all cases, the susceptibility data were fitted by the expression for a Heisenberg square-planar system. The obtained J/k values are 1.44 and 1.15 K, for the SrCu and BaCu compounds, respectively, and −0.65 and −0.59 K for the SrMn and BaMn compounds, respectively. For the manganese compounds, magnetic measurements show a magnetic ordering below 5 K which confirms the presence of a weak ferromagnetism. Thermal analyses of the phases show three different decomposition steps:  dehydration, ligand pyrolysis, and evolution of the inorganic residue for all compounds. Taking these results into account, we performed further thermal treatments to obtain mixed oxides. These were obtained at short reaction times and at temperatures lower than those of the conventional ceramic method.

Local heat generation from magnetic nanoparticles (MNPs) exposed to alternating magnetic fields can revolutionize cancer treatment. However, the application of MNPs as anticancer agents is limited by serious drawbacks. Foremost among these are the fast uptake and biodegradation of MNPs by cells and the unpredictable magnetic behavior of the MNPs when they accumulate within or around cells and tissues. In fact, several studies have reported that the heating power of MNPs is severely reduced in the cellular environment, probably due to a combination of increased viscosity and strong NP agglomeration. Herein, we present an optimized protocol to coat magnetite (Fe 3 O 4 ) NPs larger than 20 nm (FM-NPs) with high molecular weight PEG molecules that avoid collective coatings, prevent the formation of large clusters of NPs and keep constant their high heating performance in environments with very different ionic strengths and viscosities (distilled water, physiological solutions, agar and cell culture media). The great reproducibility and reliability of the heating capacity of this FM-NP@PEG system in such different environments has been confirmed by AC magnetometry and by more conventional calorimetric measurements. The explanation of this behavior has been shown to lie in preserving as much as possible the magnetic single domain-type behavior of nearly isolated NPs. In vitro endocytosis experiments in a colon cancer-derived cell line indicate that FM-NP@PEG formulations with PEGs of higher molecular weight (20 kDa) are more resistant to endocytosis than formulations with smaller PEGs (5 kDa), showing quite large uptake mean-life (τ > 5 h) in comparison with other NP systems. The in vitro magnetic hyperthermia was performed at 21 mT and 650 kHz during 1 h in a pre-endocytosis stage and complete cell death was achieved 48 h posthyperthermia. These optimal FM-NP@PEG formulations with high resistance to endocytosis and predictable magnetic response will aid the progress and accuracy of the emerging era of theranostics.

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With the aim of improving the response in magnetic hyperthermia treatments and other biomedical applications, a nanoparticle system based on nickel ferrites has been investigated. Monodisperse ferrite nanoparticles with different proportions of Ni2+ ions and sizes have been produced by an optimized synthesis based on the thermal decomposition method and the seed-growth technique. All samples were chemically and structurally characterized by different methods, and the magnetic behavior has been analyzed by means of field and temperature dependent magnetization measurements and electronic magnetic resonance. It has been proved that low proportions of Ni2+ cation in the structure favors high saturation magnetization values and a reduction of the magnetic anisotropy constant. The optimized nanoparticles were transferred to water. Such nanoparticles are innocuous at concentrations up to 0.5 mg/mL and are convenient MRI contrast agents. Those samples with lower percentages of Ni2+ atoms and bigger particle sizes presented the highest specific absorption rate, and, for instance, they are the most adequate for magnetic hyperthermia applications.