Editorial

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Open AccessEditorial

Magnetic Nanomaterials and Their Applications

by Yurii K. Gun'ko

Nanomaterials 2014, 4(2), 505-507; https://doi.org/10.3390/nano4020505 - 23 Jun 2014

Cited by 2 | Viewed by 5484

This Special Issue of Nanomaterials is dedicated to the development of new magnetic nanomaterials and their applications in biomedicine, catalysis, spintronics and other areas. The publications in this Issue demonstrate that the interest in magnetic nanomaterials is continuously growing and their realm is [...] Read more.

This Special Issue of Nanomaterials is dedicated to the development of new magnetic nanomaterials and their applications in biomedicine, catalysis, spintronics and other areas. The publications in this Issue demonstrate that the interest in magnetic nanomaterials is continuously growing and their realm is expanding rapidly. Some highlights of the publications in this issue are discussed below. [...] Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

Research

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2618 KiB

Open AccessArticle

Synthesis Characterization and Photocatalytic Studies of Cobalt Ferrite-Silica-Titania Nanocomposites

by David Greene, Raquel Serrano-Garcia, Joseph Govan and Yurii K. Gun'ko

Nanomaterials 2014, 4(2), 331-343; https://doi.org/10.3390/nano4020331 - 23 Apr 2014

Cited by 52 | Viewed by 11490

Abstract

In this work, CoFe₂O₄@SiO₂@TiO₂ core-shell magnetic nanostructures have been prepared by coating of cobalt ferrite nanoparticles with the double SiO₂/TiO₂ layer using metallorganic precursors. The Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Analysis [...] Read more.

In this work, CoFe₂O₄@SiO₂@TiO₂ core-shell magnetic nanostructures have been prepared by coating of cobalt ferrite nanoparticles with the double SiO₂/TiO₂ layer using metallorganic precursors. The Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Analysis (EDX), Vibrational Sample Magnetometer (VSM) measurements and Raman spectroscopy results confirm the presence both of the silica and very thin TiO₂ layers. The core-shell nanoparticles have been sintered at 600 °C and used as a catalyst in photo-oxidation reactions of methylene blue under UV light. Despite the additional non-magnetic coatings result in a lower value of the magnetic moment, the particles can still easily be retrieved from reaction mixtures by magnetic separation. This retention of magnetism was of particular importance allowing magnetic recovery and re-use of the catalyst. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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1063 KiB

Open AccessArticle

Hyperthermia Using Antibody-Conjugated Magnetic Nanoparticles and Its Enhanced Effect with Cryptotanshinone

by Satoshi Ota, Naoya Yamazaki, Asahi Tomitaka, Tsutomu Yamada and Yasushi Takemura

Nanomaterials 2014, 4(2), 319-330; https://doi.org/10.3390/nano4020319 - 23 Apr 2014

Cited by 20 | Viewed by 6486

Abstract

Heat dissipation by magnetic nanoparticles (MNPs) under an alternating magnetic field can be used to selectively treat cancer tissues. Antibodies conjugated to MNPs can enhance the therapeutic effects of hyperthermia by altering antibody-antigen interactions. Fe₃O₄ nanoparticles (primary diameter, 20–30 nm) [...] Read more.

Heat dissipation by magnetic nanoparticles (MNPs) under an alternating magnetic field can be used to selectively treat cancer tissues. Antibodies conjugated to MNPs can enhance the therapeutic effects of hyperthermia by altering antibody-antigen interactions. Fe₃O₄ nanoparticles (primary diameter, 20–30 nm) coated with polyethylenimine (PEI) were prepared and conjugated with CH11, an anti-Fas monoclonal antibody. HeLa cell growth was then evaluated as a function of antibody and MNP/antibody complex doses. HeLa cell growth decreased with increased doses of the antibody and complexes. However, MNPs alone did not affect cell growth; thus, only the antibody affected cell growth. In hyperthermia experiments conducted using an alternating magnetic field frequency of 210 kHz, cell viability varied with the intensity of the applied alternating magnetic field, because the temperature increase of the culture medium with added complexes was dependent on magnetic field intensity. The HeLa cell death rate with added complexes was significantly greater as compared with that with MNPs alone. Cryptotanshinone, an anti-apoptotic factor blocker, was also added to cell cultures, which provided an additional anti-cancer cell effect. Thus, an anti-cancer cell effect using a combination of magnetic hyperthermia, an anti-Fas antibody and cryptotanshinone was established. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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532 KiB

Open AccessArticle

Evaluation of Superparamagnetic Silica Nanoparticles for Extraction of Triazines in Magnetic in-Tube Solid Phase Microextraction Coupled to Capillary Liquid Chromatography

by R. A. González-Fuenzalida, Y. Moliner-Martínez, Helena Prima-Garcia, Antonio Ribera, P. Campins-Falcó and Ramon J. Zaragozá

Nanomaterials 2014, 4(2), 242-255; https://doi.org/10.3390/nano4020242 - 02 Apr 2014

Cited by 26 | Viewed by 7033

Abstract

The use of magnetic nanomaterials for analytical applications has increased in the recent years. In particular, magnetic nanomaterials have shown great potential as adsorbent phase in several extraction procedures due to the significant advantages over the conventional methods. In the present work, the [...] Read more.

The use of magnetic nanomaterials for analytical applications has increased in the recent years. In particular, magnetic nanomaterials have shown great potential as adsorbent phase in several extraction procedures due to the significant advantages over the conventional methods. In the present work, the influence of magnetic forces over the extraction efficiency of triazines using superparamagnetic silica nanoparticles (NPs) in magnetic in tube solid phase microextraction (Magnetic-IT-SPME) coupled to CapLC has been evaluated. Atrazine, terbutylazine and simazine has been selected as target analytes. The superparamagnetic silica nanomaterial (SiO₂-Fe₃O₄) deposited onto the surface of a capillary column gave rise to a magnetic extraction phase for IT-SPME that provided a enhancemment of the extraction efficiency for triazines. This improvement is based on two phenomena, the superparamegnetic behavior of Fe₃O₄ NPs and the diamagnetic repulsions that take place in a microfluidic device such a capillary column. A systematic study of analytes adsorption and desorption was conducted as function of the magnetic field and the relationship with triazines magnetic susceptibility. The positive influence of magnetism on the extraction procedure was demonstrated. The analytical characteristics of the optimized procedure were established and the method was applied to the determination of the target analytes in water samples with satisfactory results. When coupling Magnetic-IT-SPME with CapLC, improved adsorption efficiencies (60%–63%) were achieved compared with conventional adsorption materials (0.8%–3%). Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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963 KiB

Open AccessArticle

Effect of Low-Frequency AC Magnetic Susceptibility and Magnetic Properties of CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

by Yuan-Tsung Chen, Sung-Hao Lin and Tzer-Shin Sheu

Nanomaterials 2014, 4(1), 46-54; https://doi.org/10.3390/nano4010046 - 02 Jan 2014

Cited by 5 | Viewed by 6525

Abstract

In this investigation, the low-frequency alternate-current (AC) magnetic susceptibility (χ_ac) and hysteresis loop of various MgO thickness in CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ) determined coercivity (H_c) and magnetization (M_s) and correlated that with χ_ac [...] Read more.

In this investigation, the low-frequency alternate-current (AC) magnetic susceptibility (χ_ac) and hysteresis loop of various MgO thickness in CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ) determined coercivity (H_c) and magnetization (M_s) and correlated that with χ_ac maxima. The multilayer films were sputtered onto glass substrates and the thickness of intermediate barrier MgO layer was varied from 6 to 15 Å. An experiment was also performed to examine the variation of the highest χ_ac and maximum phase angle (θ_max) at the optimal resonance frequency (f_res), at which the spin sensitivity is maximal. The results reveal that χ_ac falls as the frequency increases due to the relationship between magnetization and thickness of the barrier layer. The maximum χ_ac is at 10 Hz that is related to the maximal spin sensitivity and that this corresponds to a MgO layer of 11 Å. This result also suggests that the spin sensitivity is related to both highest χ_ac and maximum phase angle. The corresponding maximum of χ_ac is related to high exchange coupling. High coercivity and saturation magnetization contribute to high exchange-coupling χ_ac strength. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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1524 KiB

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Susceptibility of CoFeB/AlO_x/Co Magnetic Tunnel Junctions to Low-Frequency Alternating Current

by Yuan-Tsung Chen and Zu-Gao Chang

Nanomaterials 2013, 3(4), 574-582; https://doi.org/10.3390/nano3040574 - 15 Oct 2013

Cited by 2 | Viewed by 6269

Abstract

This investigation studies CoFeB/AlO_x/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlO_x. The low-frequency alternate-current magnetic susceptibility (χ_ac) and phase angle (θ) of the [...] Read more.

This investigation studies CoFeB/AlO_x/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlO_x. The low-frequency alternate-current magnetic susceptibility (χ_ac) and phase angle (θ) of the CoFeB/AlO_x/Co MTJ are determined using an c_ac analyzer. The driving frequency ranges from 10 to 25,000 Hz. These multilayered MTJs are deposited on a silicon substrate using a DC and RF magnetron sputtering system. Barrier layer thicknesses are 22, 26, and 30 Å. The X-ray diffraction patterns (XRD) include a main peak at 2θ = 44.7° from hexagonal close-packed (HCP) Co with a highly (0002) textured structure, with AlO_x and CoFeB as amorphous phases. The full width at half maximum (FWHM) of the Co(0002) peak, decreases as the AlO_x thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χ_ac result demonstrates that the optimal resonance frequency (f_res) that maximizes the χ_ac value is 500 Hz. As the frequency increases to 1000 Hz, the susceptibility decreases rapidly. However, when the frequency increases over 1000 Hz, the susceptibility sharply declines, and almost closes to zero. The experimental results reveal that the mean optimal susceptibility is 1.87 at an AlO_x barrier layer thickness of 30 Å because the Co(0002) texture induces magneto-anisotropy, which improves the indirect CoFeB and Co spin exchange-coupling strength and the χ_ac value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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Open AccessArticle

Magnetism of Amorphous and Nano-Crystallized Dc-Sputter-Deposited MgO Thin Films

by Sreekanth K. Mahadeva, Jincheng Fan, Anis Biswas, K. S. Sreelatha, Lyubov Belova and K. V. Rao

Nanomaterials 2013, 3(3), 486-497; https://doi.org/10.3390/nano3030486 - 07 Aug 2013

Cited by 30 | Viewed by 7903

Abstract

We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O₂ containing working gas [...] Read more.

We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O₂ containing working gas atmosphere of (N₂ + O₂) are found to be X-ray amorphous. All these films obtained with oxygen partial pressure (P_O₂) ~10% to 80% while maintaining the same total pressure of the working gas are found to be ferromagnetic at room temperature. The room temperature saturation magnetization (M_S) value of 2.68 emu/cm³ obtained for the MgO film deposited in P_O₂ of 10% increases to 9.62 emu/cm³ for film deposited at P_O₂ of 40%. However, the M_S values decrease steadily for further increase of oxygen partial pressure during deposition. On thermal annealing at temperatures in the range 600 to 800 °C, the films become nanocrystalline and as the crystallite size grows with longer annealing times and higher temperature, M_S decreases. Our study clearly points out that it is possible to tailor the magnetic properties of thin films of MgO. The room temperature ferromagnetism in MgO films is attributed to the presence of Mg cation vacancies. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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Review

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Open AccessReview

Templated Synthesis of Magnetic Nanoparticles through the Self-Assembly of Polymers and Surfactants

by Vo Thu An Nguyen, Mario Gauthier and Olivier Sandre

Nanomaterials 2014, 4(3), 628-685; https://doi.org/10.3390/nano4030628 - 04 Aug 2014

Cited by 22 | Viewed by 16875

Abstract

The synthesis of superparamagnetic nanoparticles (NPs) for various technological applications continues to be an interesting research topic. The successful application of superparamagnetic NPs to each specific area typically depends on the achievement of high magnetization for the nanocrystals obtained, which is determined by [...] Read more.

The synthesis of superparamagnetic nanoparticles (NPs) for various technological applications continues to be an interesting research topic. The successful application of superparamagnetic NPs to each specific area typically depends on the achievement of high magnetization for the nanocrystals obtained, which is determined by their average size and size distribution. The size dispersity of magnetic NPs (MNPs) is markedly improved when, during the synthesis, the nucleation and growth steps of the reaction are well-separated. Tuning the nucleation process with the assistance of a hosting medium that encapsulates the precursors (such as self-assembled micelles), dispersing them in discrete compartments, improves control over particle formation. These inorganic-organic hybrids inherit properties from both the organic and the inorganic materials, while the organic component can also bring a specific functionality to the particles or prevent their aggregation in water. The general concept of interest in this review is that the shape and size of the synthesized MNPs can be controlled to some extent by the geometry and the size of the organic templates used, which thus can be considered as molds at the nanometer scale, for both porous continuous matrices and suspensions. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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2135 KiB

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Superparamagnetic Nanoparticles for Atherosclerosis Imaging

by Fernando Herranz, Beatriz Salinas, Hugo Groult, Juan Pellico, Ana V. Lechuga-Vieco, Riju Bhavesh and J. Ruiz-Cabello

Nanomaterials 2014, 4(2), 408-438; https://doi.org/10.3390/nano4020408 - 05 Jun 2014

Cited by 25 | Viewed by 14385

Abstract

The production of magnetic nanoparticles of utmost quality for biomedical imaging requires several steps, from the synthesis of highly crystalline magnetic cores to the attachment of the different molecules on the surface. This last step probably plays the key role in the production [...] Read more.

The production of magnetic nanoparticles of utmost quality for biomedical imaging requires several steps, from the synthesis of highly crystalline magnetic cores to the attachment of the different molecules on the surface. This last step probably plays the key role in the production of clinically useful nanomaterials. The attachment of the different biomolecules should be performed in a defined and controlled fashion, avoiding the random adsorption of the components that could lead to undesirable byproducts and ill-characterized surface composition. In this work, we review the process of creating new magnetic nanomaterials for imaging, particularly for the detection of atherosclerotic plaque, in vivo. Our focus will be in the different biofunctionalization techniques that we and several other groups have recently developed. Magnetic nanomaterial functionalization should be performed by chemoselective techniques. This approach will facilitate the application of these nanomaterials in the clinic, not as an exception, but as any other pharmacological compound. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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1022 KiB

Open AccessReview

Recent Advances in the Application of Magnetic Nanoparticles as a Support for Homogeneous Catalysts

by Joseph Govan and Yurii K. Gun'ko

Nanomaterials 2014, 4(2), 222-241; https://doi.org/10.3390/nano4020222 - 02 Apr 2014

Cited by 264 | Viewed by 16497

Abstract

Magnetic nanoparticles are a highly valuable substrate for the attachment of homogeneous inorganic and organic containing catalysts. This review deals with the very recent main advances in the development of various nanocatalytic systems by the immobilisation of homogeneous catalysts onto magnetic nanoparticles. We [...] Read more.

Magnetic nanoparticles are a highly valuable substrate for the attachment of homogeneous inorganic and organic containing catalysts. This review deals with the very recent main advances in the development of various nanocatalytic systems by the immobilisation of homogeneous catalysts onto magnetic nanoparticles. We discuss magnetic core shell nanostructures (e.g., silica or polymer coated magnetic nanoparticles) as substrates for catalyst immobilisation. Then we consider magnetic nanoparticles bound to inorganic catalytic mesoporous structures as well as metal organic frameworks. Binding of catalytically active small organic molecules and polymers are also reviewed. After that we briefly deliberate on the binding of enzymes to magnetic nanocomposites and the corresponding enzymatic catalysis. Finally, we draw conclusions and present a future outlook for the further development of new catalytic systems which are immobilised onto magnetic nanoparticles. Full article

(This article belongs to the Special Issue Magnetic Nanomaterials)

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