Nanomaterials

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4 pages, 203 KiB

Open AccessEditorial

Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications

by Victor Kuncser

Nanomaterials 2023, 13(1), 206; https://doi.org/10.3390/nano13010206 - 3 Jan 2023

Viewed by 1630

Abstract

Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility [...] Read more.

Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility of combining and inter-influencing the electronic properties of constituent interfaced nanophases. Consequently, unique physico-chemical properties of the hybrid materials of interest in various applications can be obtained. This Special Issue of Nanomaterials highlights the most advanced processing and characterization tools of some multifunctional magnetic nanocomposites and heterogeneous systems of interest in various applications, from biomedicine to sensoristics and energy-saving materials. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

Research

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24 pages, 7210 KiB

Open AccessArticle

Assisted Synthesis of Coated Iron Oxide Nanoparticles for Magnetic Hyperthermia

by Liliana P. Ferreira, César P. Reis, Tiago T. Robalo, M. E. Melo Jorge, Paula Ferreira, Joana Gonçalves, Abdollah Hajalilou and Maria Margarida Cruz

Nanomaterials 2022, 12(11), 1870; https://doi.org/10.3390/nano12111870 - 30 May 2022

Cited by 22 | Viewed by 3206

Abstract

Magnetite nanoparticles were synthesized by the co-precipitation method with and without the assistance of an additive, namely, gelatin, agar-agar or pectin, using eco-friendly conditions and materials embodying a green synthesis process. X-ray diffraction and transmission electron microscopy were used to analyze the structure [...] Read more.

Magnetite nanoparticles were synthesized by the co-precipitation method with and without the assistance of an additive, namely, gelatin, agar-agar or pectin, using eco-friendly conditions and materials embodying a green synthesis process. X-ray diffraction and transmission electron microscopy were used to analyze the structure and morphology of the nanoparticles. Magnetic properties were investigated by SQUID magnetometry and ⁵⁷Fe Mössbauer spectroscopy. The results show that the presence of the additives implies a higher reproducibility of the morphological magnetic nanoparticle characteristics compared with synthesis without any additive, with small differences associated with different additives. To assess their potential for magnetic hyperthermia, water-based suspensions of these nanoparticles were prepared with and without citric acid. The stable solutions obtained were studied for their structural, magnetic and heating efficiency properties. The results indicate that the best additive for the stabilization of a water-based emulsion and better heating efficiency is pectin or a combination of pectin and agar-agar, attaining an intrinsic loss power of 3.6 nWg⁻¹. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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15 pages, 6065 KiB

Open AccessFeature PaperArticle

Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in Au_xFe_1−x Nanophase Thin Films

by Claudiu Locovei, Cristian Radu, Andrei Kuncser, Nicusor Iacob, Gabriel Schinteie, Anda Stanciu, Sorina Iftimie and Victor Kuncser

Nanomaterials 2022, 12(7), 1176; https://doi.org/10.3390/nano12071176 - 1 Apr 2022

Cited by 4 | Viewed by 2075

Abstract

Au_xFe_1−x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, [...] Read more.

Au_xFe_1−x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mössbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect α-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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10 pages, 1698 KiB

Open AccessArticle

Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures

by Felicia Tolea, Monica Sorescu, Lucian Diamandescu, Nicusor Iacob, Mugurel Tolea and Victor Kuncser

Nanomaterials 2022, 12(6), 938; https://doi.org/10.3390/nano12060938 - 12 Mar 2022

Cited by 3 | Viewed by 1931

Abstract

MoO₂-Fe₂O₃ nanoparticle systems were successfully synthesized by mechanochemical activation of MoO₂ and α-Fe₂O₃ equimolar mixtures throughout 0–12 h of ball-milling. The role of the long-range ferromagnetism of MoO₂ on a fraction of more [...] Read more.

MoO₂-Fe₂O₃ nanoparticle systems were successfully synthesized by mechanochemical activation of MoO₂ and α-Fe₂O₃ equimolar mixtures throughout 0–12 h of ball-milling. The role of the long-range ferromagnetism of MoO₂ on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mössbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO₂, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mössbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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20 pages, 3530 KiB

Open AccessEditor’s ChoiceArticle

Coating of Magnetite Nanoparticles with Fucoidan to Enhance Magnetic Hyperthermia Efficiency

by Joana Gonçalves, Cláudia Nunes, Liliana Ferreira, Maria Margarida Cruz, Helena Oliveira, Verónica Bastos, Álvaro Mayoral, Qing Zhang and Paula Ferreira

Nanomaterials 2021, 11(11), 2939; https://doi.org/10.3390/nano11112939 - 2 Nov 2021

Cited by 15 | Viewed by 3174

Abstract

Magnetic nanoparticles (NP), such as magnetite, have been the subject of research for application in the biomedical field, especially in Magnetic Hyperthermia Therapy (MHT), a promising technique for cancer therapy. NP are often coated with different compounds such as natural or synthetic polymers [...] Read more.

Magnetic nanoparticles (NP), such as magnetite, have been the subject of research for application in the biomedical field, especially in Magnetic Hyperthermia Therapy (MHT), a promising technique for cancer therapy. NP are often coated with different compounds such as natural or synthetic polymers to protect them from oxidation and enhance their colloidal electrostatic stability while maintaining their thermal efficiency. In this work, the synthesis and characterization of magnetite nanoparticles coated with fucoidan, a biopolymer with recognized biocompatibility and antitumoral activity, is reported. The potential application of NP in MHT was evaluated through the assessment of Specific Loss Power (SLP) under an electromagnetic field amplitude of 14.7 kA m⁻¹ and at 276 kHz. For fucoidan-coated NP, it was obtained SLP values of 100 and 156 W/g, corresponding to an Intrinsic Loss Power (ILP) of 1.7 and 2.6 nHm²kg⁻¹, respectively. These values are, in general, higher than the ones reported in the literature for non-coated magnetite NP or coated with other polymers. Furthermore, in vitro assays showed that fucoidan and fucoidan-coated NP are biocompatible. The particle size (between ca. 6 to 12 nm), heating efficiency, and biocompatibility of fucoidan-coated magnetite NP meet the required criteria for MHT application. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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12 pages, 2307 KiB

Open AccessArticle

Thermal Stability, Blocking Regime and Superparamagnetic Behavior in Mn-Al-C Melt Spun Ribbons

by Alina Daniela Crisan, Aurel Leca, Ioan Dan and Ovidiu Crisan

Nanomaterials 2021, 11(11), 2898; https://doi.org/10.3390/nano11112898 - 29 Oct 2021

Cited by 2 | Viewed by 1738

Abstract

Alloys possessing nominal compositions Mn₅₃Al₄₅C₂ and Mn₅₂Al₄₆C₂ were prepared by the melt spinning method and were subjected to complex structural, morphological and magnetic investigations. As these alloys can exhibit tetragonal L1₀-type [...] Read more.

Alloys possessing nominal compositions Mn₅₃Al₄₅C₂ and Mn₅₂Al₄₆C₂ were prepared by the melt spinning method and were subjected to complex structural, morphological and magnetic investigations. As these alloys can exhibit tetragonal L1₀-type and τ phase, they have good potential as rare earth (RE)—free magnets. It is, therefore, important to monitor the ε–τ phase transformation and the stability and the magnetic features of the tetragonal phase in an entire temperature interval. By using synchrotron X-ray diffraction, it has been proven that the ε–τ phase transformation occurs gradually, with the τ phase becoming predominant only after 450 °C. Moreover, this phase has been proven to be quite stable without any grain growth even at the highest temperature investigated at 800 °C. Low temperature behavior was thoroughly investigated by using a complex combination of major and minor hysteresis loops combined with the zero field cooled-field cooled magnetization protocols (ZFC-FC). Two different regimes, blocking and superparamagnetic, were documented. A spin reorientation transition was proven to occur at 55 K while a maximum magnetization observed in ZFC-FC curves proved that at about 75 K, a transition from ferro to superparamagnetic state occurs. The existence of a blocking regime below 55 K that is characteristic to nanogranular systems with superparamagnetic behavior has shown further development towards obtaining RE-free magnets. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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10 pages, 2853 KiB

Open AccessArticle

Micron-Scale Anomalous Hall Sensors Based on Fe_xPt_1−x Thin Films with a Large Hall Angle and near the Spin-Reorientation Transition

by Kang Wang, Yiou Zhang, Shiyu Zhou and Gang Xiao

Nanomaterials 2021, 11(4), 854; https://doi.org/10.3390/nano11040854 - 27 Mar 2021

Cited by 7 | Viewed by 3093

Abstract

In this work, we fabricate and characterize an energy-efficient anomalous Hall sensor based on soft-magnetic Fe_xPt_1−x thin films with a large anomalous Hall angle. By varying the composition of the Fe_xPt_1−x alloy, its layer thickness [...] Read more.

In this work, we fabricate and characterize an energy-efficient anomalous Hall sensor based on soft-magnetic Fe_xPt_1−x thin films with a large anomalous Hall angle. By varying the composition of the Fe_xPt_1−x alloy, its layer thickness and interfacial materials, the magnetization is tuned to be near the spin transition between the perpendicular and in-plane reorientations. We performed magneto-transport and noise characterizations on anomalous Hall sensors with a small sensing area of 20 × 20 µm² in the 180 to 350 K temperature range. We found the best performance in a 1.25-nm-thick Fe_0.48Pt_0.52 sandwiched by two 1.6-nm-thick MgO layers at room temperature. The sensor has a large anomalous Hall angle of 1.95%. Moreover, it has the best field detectability of 237.5 nT/√Hz at 1 Hz and 15.3 nT/√Hz at 10 kHz, as well as a high dynamic reserve of 112.0 dB. These results suggest that the Fe_xPt_1−x alloy system is suitable for energy-efficient anomalous Hall sensors, particularly in micro-sensing applications. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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10 pages, 2886 KiB

Open AccessArticle

Improvement of Magnetic Particle Hyperthermia: Healthy Tissues Sparing by Reduction in Eddy Currents

by Alexandros Balousis, Nikolaos Maniotis and Theodoros Samaras

Nanomaterials 2021, 11(2), 556; https://doi.org/10.3390/nano11020556 - 23 Feb 2021

Cited by 10 | Viewed by 2504

Abstract

Attenuation of the unwanted heating of normal tissues due to eddy currents presents a major challenge in magnetic particle hyperthermia for cancer treatment. Eddy currents are a direct consequence of the applied alternating magnetic field, which is used to excite the nanoparticles in [...] Read more.

Attenuation of the unwanted heating of normal tissues due to eddy currents presents a major challenge in magnetic particle hyperthermia for cancer treatment. Eddy currents are a direct consequence of the applied alternating magnetic field, which is used to excite the nanoparticles in the tumor and have been shown to limit treatment efficacy in clinical trials. To overcome these challenges, this paper presents simple, clinically applicable, numerical approaches which reduce the temperature increase due to eddy currents in normal tissue and simultaneously retain magnetic nanoparticles heating efficiency within the tumor. More specifically, two protocols are examined which involve moving the heating source, an electromagnetic coil, relative to a tumor-bearing phantom tissue during the exposure. In the first protocol, the linear motion of the coil on one side with respect to the hypothesized tumor location inside the phantom is simulated. The estimated maximum temperature increase in the healthy tissue and tumor is reduced by 12% and 9%, respectively, compared to a non-moving coil, which is the control protocol. The second technique involves a symmetrical variation of the first one, where the coil is moving left and right of the phantom in a bidirectional fashion. This protocol is considered as the optimum one, since the estimated maximum temperature rise of the healthy tissue and tumor is reduced by 25% and 1%, respectively, compared to the control protocol. Thus, the advantages of a linearly moving coil are assessed through tissue sparing, rendering this technique suitable for magnetic particle hyperthermia treatment. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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17 pages, 7361 KiB

Open AccessArticle

Multifunctional GaFeO₃ Obtained via Mechanochemical Activation Followed by Calcination of Equimolar Nano-System Ga₂O₃–Fe₂O₃

by Lucian Diamandescu, Felicia Tolea, Marcel Feder, Florin Vasiliu, Ionel Mercioniu, Monica Enculescu, Traian Popescu and Bogdan Popescu

Nanomaterials 2021, 11(1), 57; https://doi.org/10.3390/nano11010057 - 29 Dec 2020

Cited by 2 | Viewed by 2310

Abstract

The equimolar oxide mixture β-Ga₂O₃—α-Fe₂O₃ was subjected to high-energy ball milling (HEBM) with the aim to obtain the nanoscaled GaFeO₃ ortho-ferrite. X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, and transmission electron microscopy were used to evidence [...] Read more.

The equimolar oxide mixture β-Ga₂O₃—α-Fe₂O₃ was subjected to high-energy ball milling (HEBM) with the aim to obtain the nanoscaled GaFeO₃ ortho-ferrite. X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, and transmission electron microscopy were used to evidence the phase structure and evolution of the equimolar nano-system β-Ga₂O₃—α-Fe₂O₃ under mechanochemical activation, either as-prepared or followed by subsequent calcination. The mechanical activation was performed for 2 h to 12 h in normal atmosphere. After 12 h of HEBM, only nanoscaled (~20 nm) gallium-doped α-Fe₂O₃ was obtained. The GaFeO₃ structure was obtained as single phase, merely after calcination at 950 °C for a couple of hours, of the sample being subjected to HEBM for 12 h. This temperature is 450 °C lower than used in the conventional solid phase reaction to obtain gallium orthoferrite. The optical and magnetic properties of representative nanoscaled samples, revealing their multifunctional character, were presented. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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19 pages, 11860 KiB

Open AccessArticle

Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes

by Claudiu Locovei, Nicolae Filipoiu, Andrei Kuncser, Anda-Elena Stanciu, Ştefan Antohe, Camelia-Florina Florica, Andreea Costas, Ionuţ Enculescu, Luc Piraux, Victor Kuncser and Vlad-Andrei Antohe

Nanomaterials 2020, 10(12), 2444; https://doi.org/10.3390/nano10122444 - 7 Dec 2020

Cited by 3 | Viewed by 2656

Abstract

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic [...] Read more.

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures’ electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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16 pages, 3532 KiB

Open AccessArticle

Controlling the Oxidation of Magnetic and Electrically Conductive Solid-Solution Iron-Rhodium Nanoparticles Synthesized by Laser Ablation in Liquids

by Ruksan Nadarajah, Shabbir Tahir, Joachim Landers, David Koch, Anna S. Semisalova, Jonas Wiemeler, Ayman El-Zoka, Se-Ho Kim, Detlef Utzat, Rolf Möller, Baptiste Gault, Heiko Wende, Michael Farle and Bilal Gökce

Nanomaterials 2020, 10(12), 2362; https://doi.org/10.3390/nano10122362 - 27 Nov 2020

Cited by 19 | Viewed by 3963

Abstract

This study focuses on the synthesis of FeRh nanoparticles via pulsed laser ablation in liquid and on controlling the oxidation of the synthesized nanoparticles. Formation of monomodal γ-FeRh nanoparticles was confirmed by transmission electron microscopy (TEM) and their composition confirmed by atom probe [...] Read more.

This study focuses on the synthesis of FeRh nanoparticles via pulsed laser ablation in liquid and on controlling the oxidation of the synthesized nanoparticles. Formation of monomodal γ-FeRh nanoparticles was confirmed by transmission electron microscopy (TEM) and their composition confirmed by atom probe tomography (APT). For these particles, three major contributors to oxidation were analysed: (1) dissolved oxygen in the organic solvents, (2) the bound oxygen in the solvent and (3) oxygen in the atmosphere above the solvent. The decrease of oxidation for optimized ablation conditions was confirmed through energy-dispersive X-ray (EDX) and Mössbauer spectroscopy. Furthermore, the time dependence of oxidation was monitored for dried FeRh nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the solution and characteristic differences of nanostrand formation between γ-FeRh and B2-FeRh nanoparticles were observed. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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18 pages, 4129 KiB

Open AccessArticle

A New Zinc Phosphate-Tellurite Glass for Magneto-Optical Applications

by Mihail Elisa, Raluca Constantina Stefan, Ileana Cristina Vasiliu, Stefan Marian Iordache, Ana-Maria Iordache, Bogdan Alexandru Sava, Lucica Boroica, Marius Catalin Dinca, Ana Violeta Filip, Aurelian Catalin Galca, Cristina Bartha, Nicusor Iacob, Madalin Ion Rusu, Mihai Eftimie and Victor Kuncser

Nanomaterials 2020, 10(9), 1875; https://doi.org/10.3390/nano10091875 - 18 Sep 2020

Cited by 18 | Viewed by 2984

Abstract

This work investigates the structural, magnetic and magneto-optical properties of a new zinc phosphate-tellurite glass belonging to the 45ZnO-10Al₂O₃-40P₂O₅-5TeO₂ system. The glass was prepared by a wet method of processing the starting reagents followed [...] Read more.

This work investigates the structural, magnetic and magneto-optical properties of a new zinc phosphate-tellurite glass belonging to the 45ZnO-10Al₂O₃-40P₂O₅-5TeO₂ system. The glass was prepared by a wet method of processing the starting reagents followed by suitable melting–stirring–quenching–annealing steps. Specific parameters such as density, average molecular mass, molar volume, oxygen packaging density, refractive index, molar refractivity, electronic polarizability, reflection loss, optical transmission, band gap and optical basicity have been reported together with thermal, magnetic and magneto-optical characteristics. Absorption bands appear in the blue and red visible region, while over 600 nm the glass becomes more transparent. FTIR and Raman spectra evidenced phosphate-tellurite vibration modes proving the P₂O₅ and TeO₂ network forming role. Magnetic measurements reveal the diamagnetic character of the Te-doped glass with an additional weak ferromagnetic signal, specific to diluted ferromagnetic oxides. Positive Faraday rotation angle with monotonous decreasing value at increasing wavelength was evidenced from magneto-optical measurements. The final product is a composite material comprising of a non-crystalline vitreous phase and Te-based nanoclusters accompanied by oxygen vacancies. The metallic-like Te colloids are responsible for the dark reddish color of the glass whereas the accompanying oxygen vacancies might be responsible for the weak ferromagnetic signal persisting up to room temperature. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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12 pages, 2213 KiB

Open AccessArticle

Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in FePt Nanocomposite Magnets

by O. Crisan, I. Dan, P. Palade, A. D. Crisan, A. Leca and A. Pantelica

Nanomaterials 2020, 10(8), 1618; https://doi.org/10.3390/nano10081618 - 18 Aug 2020

Cited by 11 | Viewed by 2670

Abstract

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. [...] Read more.

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe₅₃Pt₄₇ and Fe₅₅Pt₄₅, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L1₀ phase is formed in both alloys, coexisting with a cubic L1₂ soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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12 pages, 3681 KiB

Open AccessArticle

Magnetic Properties of SmCo₅ + 10 wt% Fe Exchange-Coupled Nanocomposites Produced from Recycled SmCo₅

by Arnab Chakraborty, Răzvan Hirian, Gregor Kapun and Viorel Pop

Nanomaterials 2020, 10(7), 1308; https://doi.org/10.3390/nano10071308 - 3 Jul 2020

Cited by 15 | Viewed by 2608

Abstract

Nanostructured alloy powders of SmCo₅ + 10 wt% Fe obtained using recycled material were studied for the first time. The SmCo₅ precursor was obtained from commercial magnets recycled by hydrogen decrepitation. The results were compared with identically processed samples obtained using [...] Read more.

Nanostructured alloy powders of SmCo₅ + 10 wt% Fe obtained using recycled material were studied for the first time. The SmCo₅ precursor was obtained from commercial magnets recycled by hydrogen decrepitation. The results were compared with identically processed samples obtained using virgin SmCo₅ raw material. The samples were synthesized by dry high-energy ball-milling and subsequent heat treatment. Robust soft/hard exchange coupling was observed—with large coercivity, which is essential for commercial permanent magnets. The obtained energy products for the recycled material fall between 80% and 95% of those obtained when using virgin SmCo₅, depending on milling and annealing times. These results further offer viability of recycling and sustainability in production. These powders and processes are therefore candidates for the next generation of specialized and nanostructured exchange-coupled bulk industrial magnets. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications)

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