Abstract:When magnetic n anop articles (MNPs) are single-domain and magnetically indep endent, their magnetic p rop erties and the conditions to optimize their efficiency in magnetic hyp erthermia app lications are now well-understood. However, the influence of magn etic interactions on magnetic hy p erthermia prop erties is still unclear. Here, we rep ort hyp erthermia and highfrequency hy steresis loop measurements on a model system consisting of M NPs with the same size but a vary ing anisotropy , which is an interesting way to tune the relative strength of magnetic interactions. A clear correlation between the M NP anisotropy and the squareness of their hy steresis loop in colloidal solution is observed : the larger the anisotropy, the smaller the squareness. Sin ce low anisotropy MNPs disp lay a squareness high er than the one of magnetically indep endent nanoparticles, magnetic interactions enhance their heatin g p ower in this case. Hysteresis loop calculations of indep endent and coup led M NPs are comp ared to exp erimental results. It is shown that the observed features are a natural consequence of the formation of chains and colu mns of MNPs during hyp erthermia exp eriments: in these structures, when the MNP magnetocristallin e anisotropy is small enough to be dominated by magnetic interactions, the hy steresis loop shap e tends to be rectan gular, which enhan ce their efficien cy. On the contrary , when MNPs do not form chains and columns, magn etic interactions reduces the hy steresis loop squareness and the efficiency of M NPs comp ared to indep endent ones. Our finding can thus exp lain contradictory results in the literature on the influence of magnetic interactions on magnetic hyp erthermia. It also p rovides an alternative exp lanation to some experiments where an enhanced specific absorp tion rate for M NPs in liqu ids has b een found comp ared to the one of MNPs in gels, usually interp reted with some contribution of the brownian motion. The p resent work should improve the understanding and interp retation of magnetic hyp erthermia exp eriments.

Abstract:Understanding the influence of dipolar interactions in magnetic hyperthermia experiments is of crucial importance for fine optimization of nanoparticle (NP) heating power. In this study, we use a kinetic Monte-Carlo algorithm to calculate hysteresis loops that correctly account for both time and temperature. This algorithm is shown to correctly reproduce the high-frequency hysteresis loop of both superparamagnetic and ferromagnetic NPs without any ad-hoc or artificial parameters. The algorithm is easily parallelizable with a good speed-up behavior, which considerably decreases the calculation time on several processors and enables the study of assemblies of several thousands of NPs. The specific absorption rate (SAR) of magnetic NPs dispersed inside spherical lysosomes is studied as a function of several key parameters: volume concentration, applied magnetic field, lysosome size, NP diameter and anisotropy. The influence of these parameters is illustrated and comprehensively explained. In summary, magnetic interactions increase the coercive field, saturation field and hysteresis area of major loops. However, for small amplitude magnetic field such as those used in magnetic hyperthermia, the heating power as function of concentration can increase, decrease or display a bell shape, depending on the relationship between the applied magnetic field and the coercive/saturation fields of the NPs. The hysteresis area is found to be well correlated with the parallel or antiparallel nature of the dipolar field acting on each particle. The heating power of a given NP is strongly influenced by a local concentration involving approximately 20 neighbors. Because this local concentration strongly decreases upon approaching the surface, the heating power increases or decreases in the vicinity of the lysosome membrane. The amplitude of variation reaches more than one order of magnitude in certain conditions. This transition occurs on a thickness corresponding to approximately 1.3 times the mean distance between two neighbors. The amplitude and sign of this variation is explained. Finally, implications of these various findings are discussed in the framework of magnetic hyperthermia optimization. It is concluded that feedback on two specific points from biology experiments is required for further advancement of the optimization of magnetic NPs for magnetic hyperthermia. The present simulations will be an advantageous tool to optimize magnetic NPs heating power and interpret experimental results. 2 Main Text:I. Introduction Studying the properties of interacting magnetic nanoparticles (MNPs) is an old topic in magnetism, driven not only by the challenge to understand the properties of a complex manybody system but also by the will to model ferrofluids, magnetic recording media or magnetotransport properties [1,2,3,4,5,6,7]. More recently, a renewed interest on this topic has been motivated by the application of MNPs in magnetic hyperthermia (MH). MH properties of magnetically independent MNPs are now well understood [8,9]...

The nanoscale manipulation and charge transport properties of the [Fe(Htrz)2(trz)](BF4) spin-crossover compound is demonstrated. Such 1D spin-crossover nanostructures are attractive building blocks for nanoelectronic switching and memory devices.

Nanotherapy using targeted magnetic nanoparticles grafted with peptidic ligands of receptors overexpressed in cancers is a promising therapeutic strategy. However, nanoconjugation of peptides can dramatically affect their properties with respect to receptor recognition, mechanism of internalization, intracellular trafficking, and fate. Furthermore, investigations are needed to better understand the mechanism whereby application of an alternating magnetic field to cells containing targeted nanoparticles induces cell death. Here, we designed a nanoplatform (termed MG-IONP-DY647) composed of an iron oxide nanocrystal decorated with a ligand of a G-protein coupled receptor, the cholecystokinin-2 receptor (CCK2R) that is overexpressed in several malignant cancers. MG-IONP-DY647 did not stimulate inflammasome of Raw 264.7 macrophages. They recognized cells expressing CCK2R with a high specificity, subsequently internalized via a mechanism involving recruitment of β-arrestins, clathrin-coated pits, and dynamin and were directed to lysosomes. Binding and internalization of MG-IONP-DY647 were dependent on the density of the ligand at the nanoparticle surface and were slowed down relative to free ligand. Trafficking of CCK2R internalized with the nanoparticles was slightly modified relative to CCK2R internalized in response to free ligand. Application of an alternating magnetic field to cells containing MG-IONP-DY647 induced apoptosis and cell death through a lysosomal death pathway, demonstrating that cell death is triggered even though nanoparticles of low thermal power are internalized in minute amounts by the cells. Together with pioneer findings using iron oxide nanoparticles targeting tumoral cells expressing epidermal growth factor receptor, these data represent a solid basis for future studies aiming at establishing the proof-of-concept of nanotherapy of cancers using ligand-grafted magnetic nanoparticles specifically internalized via cell surface receptors.

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The implementation of nano-objects in numerous emerging applications often demands their integration in macroscopic devices. Here we present the bottom-up epitaxial solution growth of high-density arrays of vertical 5 nm diameter single-crystalline metallic cobalt nanowires on wafer-scale crystalline metal surfaces. The nanowires form regular hexagonal arrays on unpatterned metallic films. These hybrid heterostructures present an important perpendicular magnetic anisotropy and pave the way to a high density magnetic recording device, with capacities above 10 Terabits/in(2). This method bypasses the need of assembling and orientating free colloidal nanocrystals on surfaces. Its generalization to other materials opens new perspectives toward many applications.

:A low-cost and simple setup for measuring the high-frequency hysteresis loops of magnetic samples is described. An AMF in the range 6-100 kHz with amplitude up to 80 mT is produced by a Litz wire coil. The latter is air-cooled using a forced-air approach so no water flow is required to run the setup. High-frequency hysteresis loops are measured using a system of

We report on the synthesis and preparation of oriented nanomaterials of single crystalline metallic Co nanorods of 6 nm in diameters and two different aspect ratios (7 and 15). They display optimized magnetic properties, with a spontaneous magnetization just below the bulk one, and large coercive fields (up to 6.5 kOe at 300 K) as a result of coherent switching (i.e., Stoner and Wohlfarth mechanism). We measured a strong effective anisotropy very close to the expected value resulting from the sum of shape and magnetocrystalline contributions. (C) 2009 American Institute of Physics. [doi:10.1063/1.3237157