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Interactions Effects in Nanoscaled Magnetic Assemblies

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A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Synthesis, Interfaces and Nanostructures".

Deadline for manuscript submissions: closed (30 January 2023) | Viewed by 29280

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Special Issue Editor

Prof. Dr. Oscar Iglesias

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Guest Editor

Department of Condensed Matter Physics and IN2UB, University of Barcelona, 08028 Barcelona, Spain
Interests: micromagnetism; exchange bias; magnetic hyperthermia; theorical modelling of nanomaterials; Monte Carlo simulations; biomedical applications; hysteresis

Special Issue Information

Dear Colleagues,

In the recent decades, the use of magnetic elements with nanoscale dimensions has spread from the typical fields of magnetic storage, spintronics and technological applications towards biomedical applications such as drug delivery, magnetic resonance imaging and magnetic hyperthermia, just to mention some examples.

Typically, an ensemble of such elements is used in applications, and, therefore, interactions between the magnetic elements are ubiquous and may give rise to magnetic collective properties that are not present at the individual element level. Examples include dipolar interactions between nanoparticles in assemblies and exchange coupling between them. Additionally of importance is the case of magnetic elements (disks, tubes, wires and so on) supporting non-uniform excitations such as domain walls, spin waves, plasmons, vortices or skyrmions, where the proximity between the elements gives rise to interactions between these excitations.

This Special Issue of Nanomaterials is aimed at featuring recent advances in studies addressing the effects that the interactions mentioned above and coupling between magnetic elements of all types have on their static and dynamic magnetic properties. The selection of articles finally published in this issue should should allow us to illustrate how we can control interactions so as to avoid their undesired effects in some cases and, at the same time, to show how their fine tuning can be exploited positively to discover new phenomena. Researchers working in the field of nanomagnetism spintronics and biomedical applications at the experimental or theoretical level are welcome to contribute with their recent findings in the field, submitting a review or original article.

Prof. Dr. Oscar Iglesias
Guest Editor

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Magnetic nanoparticles
Dipolar interactions
Magnetic hysteresis
Magnetic nanowires and nanotubes
Biomedical applications
Simulation methods
Nanomagnetism
Theoretical models
Interfacial effects
Exchange bias
DMI interactions
Magnetic vortices and skyrmions
Magnetic relaxation
Magnetic recording
Dipolar fluids

Published Papers (12 papers)

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Research

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24 pages, 2350 KiB

Open AccessArticle

Enhanced Magnetic Hyperthermia Performance of Zinc Ferrite Nanoparticles under a Parallel and a Transverse Bias DC Magnetic Field

by Constantin Mihai Lucaciu, Stefan Nitica, Ionel Fizesan, Lorena Filip, Liviu Bilteanu and Cristian Iacovita

Nanomaterials 2022, 12(20), 3578; https://doi.org/10.3390/nano12203578 - 12 Oct 2022

Cited by 4 | Viewed by 1734

Abstract

The collective organization of magnetic nanoparticles (MNPs) influences significantly their hyperthermic properties, relevant for their in vitro and in vivo applications. We report a systematic investigation of the effects of the concentration and the static bias direct current (DC) magnetic field superposed over the alternating magnetic field (AMF), both in a parallel and perpendicular configuration, on the specific absorption rate (SAR) by using zinc ferrite MNPs. The nonmonotonic dependence of the SAR on the concentration, with a maximum at very small concentrations (c ≤ 0.1 mgFe/mL), followed by a minimum at 0.25 mgFe/mL, and the second maximum of 3.3 kW/gFe at around 1 mgFe/mL, was explained by the passage of the MNPs from a single particle behavior to a collective one and the role of the dipolar interactions. By superposing a static 10 kA/m bias DC field on the AMF we obtained an increase in the SAR for both parallel and perpendicular orientations, up to 4285 W/g_Fe and 4070 W/g_Fe, respectively. To the best of our knowledge, this is the first experimental proof of a significant enhancement of the SAR produced by a perpendicular DC field. The effect of the DC field to increase the SAR is accompanied by an increase in the hyperthermia coercive field (H_cHyp) for both configurations. No enhancement of the DC fields was noticed for the MNPs immobilized in a solid matrix but the DC field increases the H_cHyp only in the parallel configuration. This translates into a higher SAR value for the perpendicular configuration as compared to the parallel configuration. These results have practical applications for magnetic hyperthermia. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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14 pages, 5092 KiB

Open AccessArticle

Dependence of Exchange Bias on Interparticle Interactions in Co/CoO Core/Shell Nanostructures

by Suchandra Goswami, Pushpendra Gupta, Sagarika Nayak, Subhankar Bedanta, Òscar Iglesias, Manashi Chakraborty and Debajyoti De

Nanomaterials 2022, 12(18), 3159; https://doi.org/10.3390/nano12183159 - 12 Sep 2022

Cited by 4 | Viewed by 1665

Abstract

This article reports the dependence of exchange bias (EB) effect on interparticle interactions in nanocrystalline Co/CoO core/shell structures, synthesized using the conventional sol-gel technique. Analysis via powder X-Ray diffraction (PXRD) studies and transmission electron microscope (TEM) images confirm the presence of crystalline phases [...] Read more.

φ

) is varied (from 20% to 1%) by the introduction of a stoichiometric amount of non-magnetic amorphous silica matrix (SiO

_{2}

) which leads to a change in interparticle interaction (separation). The influence of exchange and dipolar interactions on the EB effect, caused by the variation in interparticle interaction (separation) is studied for a series of Co/CoO core/shell nanoparticle systems. Studies of thermal variation of magnetization (

M - T

) and magnetic hysteresis loops (

M - H

) for the series point towards strong dependence of magnetic properties on dipolar interaction in concentrated assemblies whereas individual nanoparticle response is dominant in isolated nanoparticle systems. The analysis of the EB effect reveals a monotonic increase of coercivity (

H_{C}

) and EB field (

H_{E}

) with increasing volume fraction. When the nanoparticles are close enough and the interparticle interaction is significant, collective behavior leads to an increase in the effective antiferromagnetic (AFM) CoO shell thickness which results in high

H_{C}

and

H_{E}

. Moreover, in concentrated assemblies, the dipolar field superposes to the local exchange field and enhances the EB effect contributing as an additional source of unidirectional anisotropy. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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10 pages, 1569 KiB

Open AccessArticle

Strain-Tuned Spin-Wave Interference in Micro- and Nanoscale Magnonic Interferometers

by Andrey A. Grachev, Alexandr V. Sadovnikov and Sergey A. Nikitov

Nanomaterials 2022, 12(9), 1520; https://doi.org/10.3390/nano12091520 - 30 Apr 2022

Cited by 6 | Viewed by 1816

Abstract

Here, we report on the experimental study of spin-wave propagation and interaction in the double-branched Mach–Zehnder interferometer (MZI) scheme. We show that the use of a piezoelectric plate (PP) with separated electrodes connected to each branch of the MZI leads to the tunable interference of the spin-wave signal at the output section. Using a finite element method, we carry out a physical investigation of the mechanisms of the impact of distributed deformations on the magnetic properties of YIG film. Micromagnetic simulations and finite-element modelling can explain the evolution of spin-wave interference patterns under strain induced via the application of an electric field to PP electrodes. We show how the multimode regime of spin-wave propagation is used in the interferometry scheme and how scaling to the nanometer size represents an important step towards a single-mode regime. Our findings provide a simple solution for the creation of tunable spin-wave interferometers for the magnonic logic paradigm. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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18 pages, 3032 KiB

Open AccessArticle

Significant Surface Spin Effects and Exchange Bias in Iron Oxide-Based Hollow Magnetic Nanoparticles

by Pelayo García Acevedo, Manuel A. González Gómez, Ángela Arnosa Prieto, Jose S. Garitaonandia, Yolanda Piñeiro and José Rivas

Nanomaterials 2022, 12(3), 456; https://doi.org/10.3390/nano12030456 - 28 Jan 2022

Cited by 5 | Viewed by 2276

Abstract

Exchange bias (EB) properties have become especially important in hollow magnetic nanoparticles (MNPs) due to the versatility and reduced size of these materials. In this work, we present the synthesis and study of the EB properties of iron-oxide-based hollow MNPs and their precursors Fe/iron oxide MNPs with core/void/shell structure. The two mechanisms involved in EB generation were investigated: the frozen spins present in the nanograins that form the nanoparticles and the surface spins. The effect of external parameters on the coercivity (H_C), remanence (M_R), exchange bias field (H_EB) and frozen spins, such as cooling field (H_FC) and temperature, was investigated. Both H_C and H_EB present a maximum threshold above which their values begin to decrease with H_FC, showing a new trend of H_EB with H_FC and allowing modulation on demand. The existence of surface spins, present on the outer and inner surfaces, was demonstrated, and an intrinsic EB phenomenon (H_EB = 444 Oe for hollow iron oxide-based MNPs of 13.1 nm) with significant magnetization (M_S~50 emu/g) was obtained. Finally, core/void/shell MNPs of 11.9 nm prior to the formation of the hollow MNPs showed a similar behavior, with non-negligible H_EB, highlighting the importance of surface spins in EB generation. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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15 pages, 1361 KiB

Open AccessArticle

Simulating the Self-Assembly and Hysteresis Loops of Ferromagnetic Nanoparticles with Sticking of Ligands

by Nicholas R. Anderson, Jonathon Davidson, Dana R. Louie, David Serantes and Karen L. Livesey

Nanomaterials 2021, 11(11), 2870; https://doi.org/10.3390/nano11112870 - 27 Oct 2021

Cited by 5 | Viewed by 2041

Abstract

The agglomeration of ferromagnetic nanoparticles in a fluid is studied using nanoparticle-level Langevin dynamics simulations. The simulations have interdigitation and bridging between ligand coatings included using a computationally-cheap, phenomenological sticking parameter c. The interactions between ligand coatings are shown in this preliminary study to be important in determining the shapes of agglomerates that form. A critical size for the sticking parameter is estimated analytically and via the simulations and indicates where particle agglomerates transition from well-ordered (c is small) to disordered (c is large) shapes. Results are also presented for the hysteresis loops (magnetization versus applied field) for these particle systems in an oscillating magnetic field appropriate for hyperthermia applications. The results show that the clumping of particles has a significant effect on their macroscopic properties, with important consequences on applications. In particular, the work done by an oscillating field on the system has a nonmonotonic dependence on c. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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13 pages, 1263 KiB

Open AccessEditor’s ChoiceArticle

Nanoparticle Size Threshold for Magnetic Agglomeration and Associated Hyperthermia Performance

by David Serantes and Daniel Baldomir

Nanomaterials 2021, 11(11), 2786; https://doi.org/10.3390/nano11112786 - 21 Oct 2021

Cited by 14 | Viewed by 1953

Abstract

The likelihood of magnetic nanoparticles to agglomerate is usually estimated through the ratio between magnetic dipole-dipole and thermal energies, thus neglecting the fact that, depending on the magnitude of the magnetic anisotropy constant (K), the particle moment may fluctuate internally and thus undermine the agglomeration process. Based on the comparison between the involved timescales, we study in this work how the threshold size for magnetic agglomeration (

d_{a g g l}

) varies depending on the K value. Our results suggest that small variations in K-due to, e.g., shape contribution, might shift

d_{a g g l}

by a few nm. A comparison with the usual superparamagnetism estimation is provided, as well as with the energy competition approach. In addition, based on the key role of the anisotropy in the hyperthermia performance, we also analyse the associated heating capability, as non-agglomerated particles would be of high interest for the application. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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23 pages, 2565 KiB

Open AccessArticle

Structural Disorder and Collective Behavior of Two-Dimensional Magnetic Nanostructures

by David Gallina and G. M. Pastor

Nanomaterials 2021, 11(6), 1392; https://doi.org/10.3390/nano11061392 - 25 May 2021

Cited by 5 | Viewed by 2316

Abstract

Structural disorder has been shown to be responsible for profound changes of the interaction-energy landscapes and collective dynamics of two-dimensional (2D) magnetic nanostructures. Weakly-disordered 2D ensembles have a few particularly stable magnetic configurations with large basins of attraction from which the higher-energy metastable configurations are separated by only small downward barriers. In contrast, strongly-disordered ensembles have rough energy landscapes with a large number of low-energy local minima separated by relatively large energy barriers. Consequently, the former show good-structure-seeker behavior with an unhindered relaxation dynamics that is funnelled towards the global minimum, whereas the latter show a time evolution involving multiple time scales and trapping which is reminiscent of glasses. Although these general trends have been clearly established, a detailed assessment of the extent of these effects in specific nanostructure realizations remains elusive. The present study quantifies the disorder-induced changes in the interaction-energy landscape of two-dimensional dipole-coupled magnetic nanoparticles as a function of the magnetic configuration of the ensembles. Representative examples of weakly-disordered square-lattice arrangements, showing good structure-seeker behavior, and of strongly-disordered arrangements, showing spin-glass-like behavior, are considered. The topology of the kinetic networks of metastable magnetic configurations is analyzed. The consequences of disorder on the morphology of the interaction-energy landscapes are revealed by contrasting the corresponding disconnectivity graphs. The correlations between the characteristics of the energy landscapes and the Markovian dynamics of the various magnetic nanostructures are quantified by calculating the field-free relaxation time evolution after either magnetic saturation or thermal quenching and by comparing them with the corresponding averages over a large number of structural arrangements. Common trends and system-specific features are identified and discussed. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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12 pages, 1445 KiB

Open AccessArticle

Iron Oxide Nanorings and Nanotubes for Magnetic Hyperthermia: The Problem of Intraparticle Interactions

by Raja Das, Javier Alonso Masa, Vijaysankar Kalappattil, Zohreh Nemati, Irati Rodrigo, Eneko Garaio, José Ángel García, Manh-Huong Phan and Hariharan Srikanth

Nanomaterials 2021, 11(6), 1380; https://doi.org/10.3390/nano11061380 - 24 May 2021

Cited by 13 | Viewed by 2878

Abstract

Magnetic interactions can play an important role in the heating efficiency of magnetic nanoparticles. Although most of the time interparticle magnetic interactions are a dominant source, in specific cases such as multigranular nanostructures intraparticle interactions are also relevant and their effect is significant. In this work, we have prepared two different multigranular magnetic nanostructures of iron oxide, nanorings (NRs) and nanotubes (NTs), with a similar thickness but different lengths (55 nm for NRs and 470 nm for NTs). In this way, we find that the NTs present stronger intraparticle interactions than the NRs. Magnetometry and transverse susceptibility measurements show that the NTs possess a higher effective anisotropy and saturation magnetization. Despite this, the AC hysteresis loops obtained for the NRs (0–400 Oe, 300 kHz) are more squared, therefore giving rise to a higher heating efficiency (maximum specific absorption rate, SAR_max = 110 W/g for the NRs and 80 W/g for the NTs at 400 Oe and 300 kHz). These results indicate that the weaker intraparticle interactions in the case of the NRs are in favor of magnetic hyperthermia in comparison with the NTs. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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10 pages, 6921 KiB

Open AccessArticle

Spin-Resolved Quantum Scars in Confined Spin-Coupled Two-Dimensional Electron Gas

by Michael Berger, Dominik Schulz and Jamal Berakdar

Nanomaterials 2021, 11(5), 1258; https://doi.org/10.3390/nano11051258 - 11 May 2021

Cited by 2 | Viewed by 1555

Abstract

Quantum scars refer to an enhanced localization of the probability density of states in the spectral region with a high energy level density. Scars are discussed for a number of confined pure and impurity-doped electronic systems. Here, we studied the role of spin on quantum scarring for a generic system, namely a semiconductor-heterostructure-based two-dimensional electron gas subjected to a confining potential, an external magnetic field, and a Rashba-type spin-orbit coupling. Calculating the high energy spectrum for each spin channel and corresponding states, as well as employing statistical methods known for the spinless case, we showed that spin-dependent scarring occurs in a spin-coupled electronic system. Scars can be spin mixed or spin polarized and may be detected via transport measurements or spin-polarized scanning tunneling spectroscopy. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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11 pages, 1636 KiB

Open AccessCommunication

Uncovering the Magnetic Particle Imaging and Magnetic Resonance Imaging Features of Iron Oxide Nanocube Clusters

by Sahitya Kumar Avugadda, Sameera Wickramasinghe, Dina Niculaes, Minseon Ju, Aidin Lak, Niccolò Silvestri, Simone Nitti, Ipsita Roy, Anna Cristina S. Samia and Teresa Pellegrino

Nanomaterials 2021, 11(1), 62; https://doi.org/10.3390/nano11010062 - 29 Dec 2020

Cited by 14 | Viewed by 4330

Abstract

Multifunctional imaging nanoprobes continue to garner strong interest for their great potential in the detection and monitoring of cancer. In this study, we investigate a series of spatially arranged iron oxide nanocube-based clusters (i.e., chain-like dimer/trimer, centrosymmetric clusters, and enzymatically cleavable two-dimensional clusters) as magnetic particle imaging and magnetic resonance imaging probes. Our findings demonstrate that the short nanocube chain assemblies exhibit remarkable magnetic particle imaging signal enhancement with respect to the individually dispersed or the centrosymmetric cluster analogues. This result can be attributed to the beneficial uniaxial magnetic dipolar coupling occurring in the chain-like nanocube assembly. Moreover, we could effectively synthesize enzymatically cleavable two-dimensional nanocube clusters, which upon exposure to a lytic enzyme, exhibit a progressive increase in magnetic particle imaging signal at well-defined incubation time points. The increase in magnetic particle imaging signal can be used to trace the disassembly of the large planar clusters into smaller nanocube chains by enzymatic polymer degradation. These studies demonstrate that chain-like assemblies of iron oxide nanocubes offer the best spatial arrangement to improve magnetic particle imaging signals. In addition, the nanocube clusters synthesized in this study also show remarkable transverse magnetic resonance imaging relaxation signals. These nanoprobes, previously showcased for their outstanding heat performance in magnetic hyperthermia applications, have great potential as dual imaging probes and could be employed to improve the tumor thermo-therapeutic efficacy, while offering a readable magnetic signal for image mapping of material disassemblies at tumor sites. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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17 pages, 3369 KiB

Open AccessArticle

Exploring the Different Degrees of Magnetic Disorder in Tb_xR_1−xCu₂ Nanoparticle Alloys

by Elizabeth M. Jefremovas, María de la Fuente Rodríguez, Javier Alonso, Jesús Rodríguez Fernández, José Ignacio Espeso, Inés Puente-Orench, Daniel P. Rojas, Ana García-Prieto, María Luisa Fdez-Gubieda, Lidia Rodríguez Fernández and Luis Fernández Barquín

Nanomaterials 2020, 10(11), 2148; https://doi.org/10.3390/nano10112148 - 28 Oct 2020

Cited by 7 | Viewed by 2038

Abstract

Recently, potential technological interest has been revealed for the production of magnetocaloric alloys using Rare-Earth intermetallics. In this work, three series of Tb

_{x}

_{1 - x}

_{2}

(R ≡ Gd, La, Y) alloys have been produced in bulk and nanoparticle [...] Read more.

Recently, potential technological interest has been revealed for the production of magnetocaloric alloys using Rare-Earth intermetallics. In this work, three series of Tb

_{x}

_{1 - x}

_{2}

(R ≡ Gd, La, Y) alloys have been produced in bulk and nanoparticle sizes via arc melting and high energy ball milling. Rietveld refinements of the X-ray and Neutron diffraction patterns indicate that the crystalline structure in all alloys is consistent with TbCu

_{2}

orthorhombic

I m m a

bulk crystalline structure. The analyses of the DC-magnetisation (

M_{D C}

) and AC-susceptibility (

χ_{A C}

) show that three distinct degrees of disorder have been achieved by the combination of both the Tb

^{3 +}

replacement (dilution) and the nanoscaling. These disordered states are characterised by transitions which are evident to

M_{D C}

χ_{A C}

and specific heat. There exists an evolution from the most ordered Superantiferromagnetic arrangement of the Tb

_{0.5}

_{0.5}

_{2}

NPs with Néel temperature,

T_{N} \sim

27 K, and freezing temperature,

T_{f} \sim

7 K, to the less ordered weakly interacting Superparamagnetism of the Tb

_{0.1}

_{0.9}

_{2}

nanoparticles (

T_{N}

absent, and T

_{B} \sim

3 K). The Super Spin Glass Tb

_{0.5}

_{0.5}

_{2}

nanoparticles (

T_{N}

absent, and

T_{f} \sim

20 K) are considered an intermediate disposition in between those two extremes, according to their enhanced random-bond contribution to frustration. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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Review

Jump to: Research

16 pages, 2935 KiB

Open AccessReview

Magnetism of Nanoparticles: Effect of the Organic Coating

by Maryam Abdolrahimi, Marianna Vasilakaki, Sawssen Slimani, Nikolaos Ntallis, Gaspare Varvaro, Sara Laureti, Carlo Meneghini, Kalliopi N. Trohidou, Dino Fiorani and Davide Peddis

Nanomaterials 2021, 11(7), 1787; https://doi.org/10.3390/nano11071787 - 9 Jul 2021

Cited by 41 | Viewed by 3271

Abstract

The design of novel multifunctional materials based on nanoparticles requires tuning of their magnetic properties, which are strongly dependent on the surface structure. The organic coating represents a unique tool to significantly modify the surface structure trough the bonds between the ligands of the organic molecule and the surface metal atoms. This work presents a critical overview of the effects of the organic coating on the magnetic properties of nanoparticles trough a selection of papers focused on different approaches to control the surface structure and the morphology of nanoparticles’ assemblies. Full article

(This article belongs to the Special Issue Interactions Effects in Nanoscaled Magnetic Assemblies)

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