Colloidal magnetic nanocrystal clusters: variable length-scale interaction mechanisms, synergetic functionalities and technological advantages

Abstract

Magnetic particles of optimized nanoscale dimensions can be utilized as building blocks to generate colloidal nanocrystal assemblies with controlled size, well-defined morphology, and tailored properties. Recent advances in the state-of-the-art surfactant-assisted approaches for the directed aggregation of inorganic nanocrystals into cluster-like entities are discussed, and the synthesis parameters that determine their geometrical arrangement are highlighted. This review pays attention to the enhanced physical properties of iron oxide nanoclusters, while it also points to their emerging collective magnetic response. The current progress in experiment and theory for evaluating the strength and the role of intra-and inter-cluster interactions is analyzed in view of the spatial arrangement of the component nanocrystals. Numerous approaches have been proposed for the critical role of dipole-dipole and exchange interactions in establishing the nature of the nanoclusters' cooperative magnetic behavior (be it ferromagnetic or spin-glass like). Finally, we point out why the purposeful engineering of the nanoclusters' magnetic characteristics, including their surface functionality, may facilitate their use in diverse technological sectors ranging from nanomedicine and photonics to catalysis.

The Role of Magnetic Nanoparticles in Cancer Nanotheranostics

“…The shape-induced magnetic anisotropy interferes with magnetization reversal due to thermal fluctuations and affects the heating efficiency of NPs [52]. On this basis, higher heating capacity and magnetization saturation values have been associated and demonstrated in cubic ferrite MNPs (of lower surface anisotropy) when compared to spherical MNPs of the same size [19,27,53].…”

Remanence Plots as a Probe of Spin Disorder in Magnetic Nanoparticles

“…[8][9][10] Magnetic interactions control the properties of sufficiently dense assemblies of magnetic nanoparticles and nanostructures, tailoring their functional properties, e.g., blocking (or freezing) temperature, coercivity, remanent magnetization, switching-field distribution and effective anisotropy, among others. [11][12][13][14][15][16] In fact, interactions are the basis of a large number of nanoparticle-based magnetic materials, e.g., superferromagnets, superspin glasses, artificial spin ice, long range self-assemblies, or ferrofluids. 15,[17][18][19][20][21] Given the crucial importance of interactions in magnetic nanostructures, many direct and indirect approaches have been used to try to quantify them: first order reversal curve (FORC) analysis, 22,23 small angle neutron scattering, SANS, [24][25][26][27] electron holography, 28,29 magnetic force microscopy, 30,31 Lorentz microscopy, 32 Brillouin light scattering, 33 resonant magnetic x-ray scattering 34 and so on.…”

“…15,[17][18][19][20][21] Given the crucial importance of interactions in magnetic nanostructures, many direct and indirect approaches have been used to try to quantify them: first order reversal curve (FORC) analysis, 22,23 small angle neutron scattering, SANS, [24][25][26][27] electron holography, 28,29 magnetic force microscopy, 30,31 Lorentz microscopy, 32 Brillouin light scattering, 33 resonant magnetic x-ray scattering 34 and so on. However, one of the most accepted methods to assess interactions is the remanence plots technique (i.e., Henkel or δM plots), [35][36][37] which is routinely used to evaluate interactions between nanoparticles or grains [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] both in fundamental studies 56,57 and in diverse nanoparticle-based applications (e.g., patterned recording media, permanent magnets, or magnetic resonance imaging 11,38,…”

Preparation and Application of Iron Oxide Nanoclusters

“…Magnetic iron oxide nanoclusters, which refers to a group of individual nanoparticles, have recently attracted much attention because of their distinctive behaviors compared to individual nanoparticles [1][2][3]. The magnetic properties of iron oxide nanoparticles are strongly dependent on size, yielding single-domain regimes and a superparamagnetic limit [4].…”

“…Magnetic iron oxide nanoclusters combine the properties of individual nanoparticles and exhibit collective behaviors due to interactions between individual nanoparticles [3]. In addition, the collective behaviors of these nanoclusters can be controlled by tuning the size and shape of individual nanoparticles, the interspacing between nanoparticles, and the properties of the capping molecules of individual nanoparticles [2,3,6]. Particularly, magnetic nanoclusters can be manipulated with applied magnetic fields, leading to novel functional materials.…”