M. Corti

One-Pot Synthesis and Characterization of Size-Controlled Bimagnetic FePt−Iron Oxide Heterodimer Nanocrystals

A one-pot, two-step colloidal strategy to prepare bimagnetic hybrid nanocrystals (HNCs), comprising size-tuned fcc FePt and inverse spinel cubic iron oxide domains epitaxially arranged in a heterodimer configuration, is described. The HNCs have been synthesized in a unique surfactant environment by temperature-driven sequential reactions, involving the homogeneous nucleation of FePt seeds and the subsequent heterogeneous growth of iron oxide. This self-regulated mechanism offers high versatility in the control of the geometric features of the resulting heterostructures, circumventing the use of more elaborate seeded growth techniques. It has been found that, as a consequence of the exchange coupling between the two materials, the HNCs exhibit tunable single-phase-like magnetic behavior, distinct from that of their individual components. In addition, the potential of the heterodimers as effective contrast agents for magnetic resonance imaging techniques has been examined.

Bovine serum albumin-based magnetic nanocarrier for MRI diagnosis and hyperthermic therapy: a potential theranostic approach against cancer.

The scientific communityis seeking to exploit the intrinsic properties of magneticnanoparticles (MNPs) to obtain medical breakthroughs indiagnosisandtherapy.OneofthemainadvantagesofmagneticNPs is that they can be visualized acting as magnetic contrastagents(CA)formagneticresonanceimaging(MRI).Heatedina high-frequency magnetic field they trigger drug release orproducehyperthermia/ablationoftissues,currentlyreportedasmagnetic fluid hyperthermia (MFH). Accordingly, the termtheranostic nanomedicine has been defined as an integratednanotherapeutic system, which can diagnose, provide targetedtherapy and monitor the response to therapy.

Cyano-bridged coordination polymer nanoparticles with high nuclear relaxivity: toward new contrast agents for MRI.

New water-soluble paramagnetic Gd-containing cyano-bridged metallic coordination polymer nanoparticles with a chitosan shell show high nuclear relaxivity in acidic water which is up to six times higher than that of the actually used Gd-chelates.

Magnetic and relaxation properties of multifunctional polymer-based nanostructured bioferrofluids as MRI contrast agents

A series of maghemite/polymer composite ferrofluids with variable magnetic core size, which show a good efficiency as MRI contrast agents, are presented. These ferrofluids are biocompatible and can be proposed as possible platforms for multifunctional biomedical applications, as they contain anchoring groups for biofunctionalization, can incorporate fluorescent dyes, and have shown low cellular toxicity. The magnetic properties of the ferrofluids have been determined by means of magnetization and ac susceptibility measurements as a function of temperature and frequency. The NMR dispersion profiles show that the low frequency behavior of the longitudinal relaxivity r1 is well described by the heuristic model of 1H nuclear relaxation induced by superparamagnetic nanoparticles proposed by Roch and co‐workers. The contrast efficiency parameter, i.e., the nuclear transverse relaxivity r2, for samples with d > 10 nm assumes values comparable with or better than the ones of commercial samples, the best results obtained in particles with the biggest magnetic core, d = 15 nm. The contrast efficiency results are confirmed by in vitro MRI experiments at ν = 8.5 MHz, thus allowing us to propose a set of optimal microstructural parameters for multifunctional ferrofluids to be used in MRI medical diagnosis. Magn Reson Med, 2011.

Magnetic and relaxometric properties of Mn ferrites

We present the magnetic properties and the 1H nuclear magnetic resonance dispersion profiles of Mn-ferrites-based compounds, as possible novel contrast agents (CAs) for magnetic resonance imaging (MRI). The samples consist of nanoparticles (NPs) with the magnetic core made of Mn1+xFe2−xO4, obtained by the rapid decomposition of metalcarbonyl into a hot solvent containing an oxidizer and a coordinating surfactant; by this procedure, monodisperse capped NPs with different sizes have been obtained. We have performed structural and morphological investigation by x-ray powder diffraction and transmission electron microscopy techniques and SQUID magnetometry experiments to investigate the magnetic behaviour of the samples. As required for MRI applications using negative CAs, the samples are superparamagnetic at room temperature, having blocking temperatures in the range 14–80 K. The longitudinal r1 and transverse r2 nuclear relaxivities appear to vary strongly with the magnetic core size, their values being comparable to commercial compounds in the high-frequency range ν > 100 MHz. The experimental results suggest that our samples are suitable for high-frequency MRI imagers in general and in particular for the 3 T clinical imager, as indeed suggested by a recent report (Tromsdorf et al 2007 Nanoletters 7 2422).

Magnetic correlations and 139La NQR relaxation in La2−x Sr x CuO4−y

Summary139La NQR spin-spin and spin-lattice relaxation measurements in La2−xSrxCuO4−y are presented, for x ranging from zero to 0.3 and for variable oxygen content, in the temperature range (1.6÷450) K. The data are analysed in terms of the different possible relaxation mechanisms. The dominant relaxation mechanism over most of the x and T range is associated with the Cu++−Cu++ magnetic correlations and spin dynamics. To explain the data we introduce a heuristic model whereby the degree of magnetic correlations, that would result from the strength of the Cu−Cu exchange coupling, is reduced by mobile charge defects (solitons or holons) causing a liquidlike thermal bath of magnetic excitations described by a concentration-dependent and thermally activated correlation time τd. The activation energy for τd is inversely proportional to the concentration of mobile defects. It is shown that the T1 data yield the x and T dependence of the correlation length, with quantitative estimate in agreement with neutron scattering results. Some implications of the model on other quantities, like magnetic susceptibility, x dependence of the Neel temperature and electric conductivity, are briefly discussed.RiassuntoSono presentate misure di rilassamento NQR spin-spin e spin-reticolo per 139La in La2−xSrxCuO4−y, per x compreso tra 0 e 0.3 e a contenuto variabile di ossigeno, nell’intervallo di temperatura T tra 1.6 e 450 K. I risultati delle misure vengono dapprima analizzati alla luce dei possibili meccanismi di rilassamento e si mostra come in un ampio intervallo di valori di x e di T il meccanismo dominante è costituito dalla dinamica e dalle correlazioni degli spin di Cu++. Allo scopo di spiegare i risultati ottenuti, viene introdotto un modello euristico in cui il grado di correlazione magnetica che conseguirebbe dall’interazione di superscambio Cu−Cu viene ridotto da difetti mobili (solitoni o holoni) che insediano un bagno termico di eccitazioni magnetiche simile a un liquido, descritto da un tempo di correlazione τd che dipende dalla concentrazione di tali difetti ed è termicamente attivato. L’energia di attivazione per τd risulta inversamente proporzionale alla concentrazione di difetti mobili. Oltre a giustificare compiutamente le risultanze sperimentali, tale modello consente di ricavare quantitativamente la dipendenza da x e da T della lunghezza di correlazione, che risulta in accordo con quella nota a T=77K dallo scattering di neutroni. Sono anche brevemente discusse le implicazioni del modello su altre grandezze come la suscettività magnetica, la dipendenza della temperatura di Neel da x e la conducibilità elettrica.РезюмеПриводятся результаты измерений 139La NQR спин-спиновой и спинрешеточной релаксации в La2−xSrxCuO4−y для x в области от 0 до x=0.3 и для различного содержания кислорода, в области температур (1.6÷450)K. Полученные данные анализируются в терминах различных механизмов релаксации. Доминиркющий механизм релаксации для большенства значений x и в рассматриваемой области температур связан с магнитными корреляциями Cu++−Cu++ и спиновой динамикой. Для объяснения полученных данных мы вводим эвристическую модель, с помощью которой степень магнитных корреляций, которые зависят от силы Cu−Cu обменной связи, сводится к подвижным заряженным дефектам (солитовы или голоны), обусловленным термостатом магнитных возбужений, описываемых зависящим от концентрации и термически активированным временем корреляции τd. Энергия активации для τd обратно пропорциональна концентрации подвижных дефектов. Показывается, что данные для T1 определяют зависимость корреляции от x и от T, причем количественная оценка согласуется с данными по рассеянию нейтронов. Вкратце обсуждаются возможные применения предложенной модели к другим величинам: магнитной восприимчивости, зависимости температуры Нееля (точки Кюри) от x и электропроводности.

NMR-D study of the local spin dynamics and magnetic anisotropy in different nearly monodispersed ferrite nanoparticles

We present a systematic experimental comparison of the superparamagnetic relaxation time constants obtained by means of dynamic magnetic measurements and (1)H-NMR relaxometry, on ferrite-based nanosystems with different composition, various core sizes and dispersed in different solvents. The application of a heuristic model for the relaxivity allowed a comparison between the reversal time of magnetization as seen by NMR and the results from the AC susceptibility experiments, and an estimation of fundamental microscopic properties. A good agreement between the NMR and AC results was found when fitting the AC data to a Vogel-Fulcher law. Key parameters obtained from the model have been exploited to evaluate the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate the minimum approach distance of the bulk solvent.

Spin dynamics and energy gap of a Fe dimer from susceptibility and 1H nuclear magnetic resonance

The iron(III) S=5/2 dimer [Fe(OMe)(dbm)2]2 (in short Fe2) has a nonmagnetic S=0 ground state. The separation between the singlet ground state and the first excited (triplet) state is determined from susceptibility measurements to be about 22 K; for a dimer this value is equal to the antiferromagnetic exchange constant J. Proton nuclear magnetic resonance measurements were performed on Fe2. The nuclear spin-lattice relaxation rate (NSLR) was studied as a function of temperature at 31 and 67 MHz and as a function of the resonance frequency (10–67 MHz) at T=295 K. At room temperature the 1H NSLR is independent of frequency contrary to the strong dependence found in planar ring compounds like Fe6 and ferric wheel (Fe10). The temperature dependence of the proton NSLR shows an exponential decrease on lowering the temperature from which we estimate a gap value about double the value obtained from the uniform susceptibility, a result which is unexpected if the NSLR were simply proportional to the concentration of...

Slice-selection method for topical NMR in solids

Abstract A method to perform NMR and relaxation measurements in narrow slices or lines of a solid is described. The method is based on acquisition and averaging of free induction decays with stepped field gradients. An FID signal is recorded for a given gradient; after a time of the order of T1 another gradient is applied and the FID is coadded to the previous one, et cetera. The method has the peculiarity of requiring H1 only of the order of the intrinsic linewidth while the maximum gradient can be increased up to a value giving offsets much larger than H1.

Tilt-wave dynamics of the oxygen octahedra in La 2 CuO 4 from anelastic and 139 La NQR relaxation

The anharmonic vibrational dynamics in nearly stoichiometric