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Single crystalline magnetic FeCo nanostars were prepared using an organometallic approach under mild conditions. The fine-tuning of the experimental conditions allowed the direct synthesis of these nano-octopods with body-centered cubic ( bcc ) structure through a one-pot reaction, contrarily to the seed-mediated growth classically used. The FeCo nanostars consist of 8 tetrahedrons exposing {311} facets, as revealed by high resolution transmission electron microscopy (HRTEM) imaging and electron tomography (ET), and exhibit a high magnetization comparable with the bulk one ( M s = 235 A·m 2 ·kg -1 ). Complex 3D spin configurations resulting from the competition between dipolar and exchange interactions are revealed by electron holography. This spin structures are stabilized by the high aspect ratio tetrahedral branches of the nanostars, as confirmed by micromagnetic simulations. This illustrates how magnetic properties can be significantly tuned by nanoscale shape control.

Single-crystalline FeCo nanoparticles with tunable size and shape were prepared by co-decomposing two metal-amide precursors under mild conditions. The nature of the ligands introduced in this organometallic synthesis drastically affects the reactivity of the precursors and, thus, the chemical distribution within the nanoparticles. The presence of the B2 short-range order was evidenced in FeCo nanoparticles prepared in the presence of HDAHCl ligands, combining 57 Fe Mössbauer, zero-field 59 Co ferromagnetic nuclear resonance (FNR), and X-ray diffraction studies. This is the first time that the B2 structure is directly formed during synthesis without the need of any annealing step. The as-prepared nanoparticles exhibit magnetic properties comparable with the ones for the bulk ( M s = 226 Am 2 ·kg -1 ). Composite magnetic materials prepared from these FeCo nanoparticles led to a successful proof-of-concept of the integration on inductor-based filters (27% enhancement of the inductance value at 100 MHz).

The different spin configurations in the vicinity of the single-domain/vortex transition are reported in isolated magnetic nanoparticles. By combining chemical synthesis, electron holography in a dedicated transmission electron microscope and micromagnetic simulations, we establish the "magnetic configurations vs size" phase diagram of Fe single-crystalline nanocubes. Room temperature high resolution magnetic maps reveal the transition between single-domain and vortex states for Fe nanocubes from 25 to 27 nm, respectively. An intermediate spin configuration consisting of an ⟨111⟩ vortex is for the first time evidenced.

Addition of Co2(Co)9 and Ru3(CO)12 on preformed monodisperse iron(0) nanoparticles (Fe(0) NPs) at 150 °C under H2 leads to monodisperse core-shell Fe@FeCo NPs and to a thin discontinuous Ru(0) layer supported on the initial Fe(0) NPs. The new complex NPs were studied by state-of-the-art transmission electron microscopy techniques as well as X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. These particles display large heating powers (SAR) when placed in an alternating magnetic field. The combination of magnetic and surface catalytic properties of these novel objects were used to demonstrate a new concept: the possibility of performing Fischer-Tropsch syntheses by heating the catalytic nanoparticles with an external alternating magnetic field.

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.

We report a tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability. This process based on the decomposition of Fe(CO)(5) on Fe(0) seeds allows the control of the amount of carbon diffused and therefore the tuning of nanoparticles magnetic anisotropy. This results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments.

We report a chemical method to prepare metallic Fe porous nanocubes. The presence of pores embedded inside the cubes was attested by electron tomography. Thanks to electronic holography and micromagnetic simulations, we show that the presence of these defects stabilizes the vortices in assembly of interacting cubes. These results open new perspectives toward magnetic vortex stabilization at relatively low cost for various applications (microelectronics, magnetic recording, or biological applications).

We report on room temperature magnetoresistance in networks of chemically synthesized metallic Fe nanoparticles surrounded by two types of organic barriers. Electrical properties, featuring Coulomb blockade, and magnetotransport measurements show that this magnetoresistance arises from spin-dependent tunnelling, so the organic ligands stabilizing the nanoparticles are efficient spin-conservative tunnel barrier. These results demonstrate the feasibility of an all-chemistry approach for room temperature spintronics.