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11 pages, 5849 KiB

Open AccessArticle

Structural and Magnetic Properties of Inverse-Heusler Mn₂FeSi Alloy Powder Prepared by Ball Milling

by Ondřej Životský, Kateřina Skotnicová, Tomáš Čegan, Jan Juřica, Lucie Gembalová, František Zažímal and Ivo Szurman

Materials 2022, 15(3), 697; https://doi.org/10.3390/ma15030697 - 18 Jan 2022

Cited by 9 | Viewed by 2300

Abstract

Ternary Mn₂FeSi alloy was synthesized from pure elemental powders by mechanical alloying, using a high-energy planetary ball mill. The formation of an inverse-Heusler phase after 168 h of milling and subsequent annealing at 1173 K for 1.5 h was confirmed by [...] Read more.

Ternary Mn₂FeSi alloy was synthesized from pure elemental powders by mechanical alloying, using a high-energy planetary ball mill. The formation of an inverse-Heusler phase after 168 h of milling and subsequent annealing at 1173 K for 1.5 h was confirmed by X-ray diffraction. The diffractogram analysis yielded XA structure and the lattice parameter 0.5677 nm in a good agreement with the theoretically obtained value of 0.560 nm. The final powder was formed by particles of irregular shape and median diameter D50 of 3.8 μm and their agglomerates. The chemical analysis resulted in the mean composition of 49.0 at.% Mn, 25.6 at.% Fe and 25.4 at.% Si. At room temperature, the prepared samples featured a heterogeneous magnetic structure consisting of dominant paramagnetic phase confirmed by Mössbauer spectrometry and a weak ferro-/ferrimagnetic contribution detected by magnetization curves. From the field-cooled and zero-field-cooled curves the Néel temperature of 67 K was determined. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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25 pages, 3272 KiB

Open AccessArticle

Effect of Grinding and the Mill Type on Magnetic Properties of Carboxylated Multiwall Carbon Nanotubes

by Agnieszka Jamrozik, Janusz Przewoznik, Sonia Krysiak, Jozef Korecki, Grzegorz Trykowski, Artur Małolepszy, Leszek Stobiński and Kvetoslava Burda

Materials 2021, 14(14), 4057; https://doi.org/10.3390/ma14144057 - 20 Jul 2021

Cited by 2 | Viewed by 2169

Abstract

The influence of the grinding process on the magnetic properties of as prepared and functionalized multiwall carbon nanotubes (MWCNTs) is presented. We have observed that 3 h mechanical grinding at 400 rpm in contrast to functionalization does not remove the iron contamination from [...] Read more.

The influence of the grinding process on the magnetic properties of as prepared and functionalized multiwall carbon nanotubes (MWCNTs) is presented. We have observed that 3 h mechanical grinding at 400 rpm in contrast to functionalization does not remove the iron contamination from MWCNTs. However, it changes the Fe chemical states. The magnetic properties of iron nanoparticles (Fe-NPs) embedded in the carbon matrix of MWCNTs have been analyzed in detail. We have proven that single-domain non-interacting Fe_(C,O)-NPs enriched in the Fe₃C phase (~10 nm) enclosed inside these nanotubes are responsible for their magnetic properties. Mechanical grinding revealed a unique impact of -COOH groups (compared to -COONH₄ groups) on the magnetism of functionalized MWCNTs. In MWCNT-COOH ground in a steel mill, the contribution of the Fe₂O₃ and α-Fe phases increased while the content of the magnetically harder Fe₃C phase decreased. This resulted in a 2-fold coercivity (H_c) decrease and saturation magnetization (M_S) increase. A 2-fold remanence (M_r) decrease in MWCNT-COOH ground in an agate mill is related to the modified Fe_(C,O)-NP magnetization dynamics. Comparison of the magnetostatic exchange and effective anisotropy length estimated for Fe_(C,O)-NPs allows concluding that the anisotropy energy barrier is higher than the magnetostatic energy barrier. The enhanced contribution of surface anisotropy to the effective anisotropy constant and the unique effect of the -COOH groups on the magnetic properties of MWCNTs are discussed. The procedure for grinding carboxylated MWCNTs with embedded iron nanoparticles using a steel mill has a potential application for producing Fe-C nanocomposites with desired magnetic properties. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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12 pages, 4724 KiB

Open AccessArticle

Influence of Dissolving Fe–Nb–B–Dy Alloys in Zirconium on Phase Structure, Microstructure and Magnetic Properties

by Grzegorz Ziółkowski, Artur Chrobak, Ewa Talik, Joanna Klimontko and Dariusz Chrobak

Materials 2021, 14(10), 2526; https://doi.org/10.3390/ma14102526 - 12 May 2021

Viewed by 1535

Abstract

This paper refers to the structural and magnetic properties of [(Fe₈₀Nb₆B₁₄)_0.88Dy_0.12]_1−xZr_x (x = 0; 0.01; 0.02; 0.05; 0.1; 0.2; 0.3; 0.5) alloys obtained by the vacuum mold suction casting [...] Read more.

This paper refers to the structural and magnetic properties of [(Fe₈₀Nb₆B₁₄)_0.88Dy_0.12]_1−xZr_x (x = 0; 0.01; 0.02; 0.05; 0.1; 0.2; 0.3; 0.5) alloys obtained by the vacuum mold suction casting method. The analysis of the phase contribution indicated a change in the compositions of the alloys. For x < 0.05, occurrence of the dominant Dy₂Fe₁₄B phase was observed, while a further increase in the Zr content led to the increasing contribution of the Fe–Zr compounds and, simultaneously, separation of crystalline Dy. The dilution of (Fe₈₀Nb₆B₁₄)_0.88Dy_0.12 in Zr strongly influenced the magnetization processes of the examined alloys. Generally, with the increasing x parameter, we observed a decrease in coercivity; however, the unexpected increase in magnetic saturation and remanence for x = 0.2 and x = 0.3 was shown and discussed. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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20 pages, 5217 KiB

Open AccessArticle

Correlation between Microstructure and Magnetism in Ball-Milled SmCo₅/α-Fe (5%wt. α-Fe) Nanocomposite Magnets

by Anna Bajorek, Paweł Łopadczak, Krystian Prusik and Maciej Zubko

Materials 2021, 14(4), 805; https://doi.org/10.3390/ma14040805 - 8 Feb 2021

Cited by 7 | Viewed by 2651

Abstract

Magnetic nanocomposites SmCo₅/α-Fe were synthesized mechanically by high-energy ball milling (HEBM) from SmCo₅ and 5%wt. of α-Fe powders. The X-ray diffraction analysis reveals the hexagonal 1:5 phase as the main one accompanied by the cubic α-Fe phase and 2:17 rhombohedral [...] Read more.

Magnetic nanocomposites SmCo₅/α-Fe were synthesized mechanically by high-energy ball milling (HEBM) from SmCo₅ and 5%wt. of α-Fe powders. The X-ray diffraction analysis reveals the hexagonal 1:5 phase as the main one accompanied by the cubic α-Fe phase and 2:17 rhombohedral as the secondary phase. The content of each detected phase is modified throughout the synthesis duration. A significant decrease in crystallite size with a simultaneous increase in lattice straining is observed. A simultaneous gradual reduction in particle size is noted from the microstructural analysis. Magnetic properties reveal non-linear modification of magnetic parameters associated with the strength of the exchange coupling induced by various duration times of mechanical synthesis. The highest value of the maximum energy product (BH)_max at room temperature is estimated for samples milled for 1 and 6 h. The intermediate mixed-valence state of Sm ions is confirmed by electronic structure analysis. An increase in the Co magnetic moment versus the milling time is evidenced based on the performed fitting of the Co3s core level lines. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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10 pages, 2916 KiB

Open AccessArticle

Effect of Electronic Correlations on the Electronic Structure, Magnetic and Optical Properties of the Ternary RCuGe Compounds with R = Tb, Dy, Ho, Er

by Alexey V. Lukoyanov, Lubov N. Gramateeva, Yury V. Knyazev, Yury I. Kuz’min, Sachin Gupta and K. G. Suresh

Materials 2020, 13(16), 3536; https://doi.org/10.3390/ma13163536 - 11 Aug 2020

Cited by 3 | Viewed by 1896

Abstract

In this study, the ab initio and experimental results for RCuGe ternary intermetallics were reported for R = Tb, Dy, Ho, Er. Our theoretical calculations of the electronic structure, employing local spin density approximation accounting for electron–electron correlations in the 4f shell of [...] Read more.

In this study, the ab initio and experimental results for RCuGe ternary intermetallics were reported for R = Tb, Dy, Ho, Er. Our theoretical calculations of the electronic structure, employing local spin density approximation accounting for electron–electron correlations in the 4f shell of Tb, Dy, Ho, Er ions were carried in DFT+U method. The optical properties of the RCuGe ternary compounds were studied at a broad range of wavelengths. The spectral and electronic characteristics were obtained. The theoretical electron densities of states were taken to interpret the experimental energy dependencies of the experimental optical conductivity in the interband light–absorption region. From the band calculations, the 4f shell of the rare-earth ions was shown to provide the major contribution to the electronic structure, magnetic and optical properties of the RCuGe intermetallics. The accounting for electron–electron correlations in Tb, Dy, Ho, Er resulted in a good agreement between the calculated and experimental magnetic and optical characteristics. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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15 pages, 3226 KiB

Open AccessArticle

Europium Doping Impact on the Properties of MBE Grown Bi₂Te₃ Thin Film

by Katarzyna Balin, Marcin Wojtyniak, Mateusz Weis, Maciej Zubko, Bartosz Wilk, Ruizhe Gu, Pascal Ruello and Jacek Szade

Materials 2020, 13(14), 3111; https://doi.org/10.3390/ma13143111 - 13 Jul 2020

Cited by 5 | Viewed by 2910

Abstract

The impact of europium doping on the electronic and structural properties of the topological insulator Bi₂Te₃ is studied in this paper. The crystallographic structure studied by electron diffraction and transmission microscopy confirms that grown by Molecular Beam Epitaxy (MBE) system [...] Read more.

The impact of europium doping on the electronic and structural properties of the topological insulator Bi₂Te₃ is studied in this paper. The crystallographic structure studied by electron diffraction and transmission microscopy confirms that grown by Molecular Beam Epitaxy (MBE) system film with the Eu content of about 3% has a trigonal structure with relatively large monocrystalline grains. The X-ray photoemission spectroscopy indicates that europium in Bi₂Te₃ matrix remains divalent and substitutes bismuth in a Bi₂Te₃ matrix. An exceptional ratio of the photoemission 4d multiplet components in Eu doped film was observed. However, some spatial inhomogeneity at the nanometer scale is revealed. Firstly, local conductivity measurements indicate that the surface conductivity is inhomogeneous and is correlated with a topographic image revealing possible coexistence of conducting surface states with insulating regions. Secondly, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) depth-profiling also shows partial chemical segregation. Such in-depth inhomogeneity has an impact on the lattice dynamics (phonon lifetime) evaluated by femtosecond spectroscopy. This unprecedented set of experimental investigations provides important insights for optimizing the process of growth of high-quality Eu-doped thin films of a Bi₂Te₃ topological insulator. Understanding such complex behaviors at the nanoscale level is a necessary step before considering topological insulator thin films as a component of innovative devices. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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Review

Jump to: Research

23 pages, 1582 KiB

Open AccessReview

Structure and Magnetic Properties of Intermetallic Rare-Earth-Transition-Metal Compounds: A Review

by Lotfi Bessais

Materials 2022, 15(1), 201; https://doi.org/10.3390/ma15010201 - 28 Dec 2021

Cited by 11 | Viewed by 2729

Abstract

This review discusses the properties of candidate compounds for semi-hard and hard magnetic applications. Their general formula is

R_{1 - s} T_{5 + 2 s}

with R = rare earth, T = transition metal and [...] Read more.

This review discusses the properties of candidate compounds for semi-hard and hard magnetic applications. Their general formula is

R_{1 - s} T_{5 + 2 s}

with R = rare earth, T = transition metal and

0 \leq s \leq 0.5

and among them, the focus will be on the ThMn

_{12}

- and Th

_{2}

Zn

_{17}

-type structures. Not only will the influence of the structure on the magnetic properties be shown, but also the influence of various R and T elements on the intrinsic magnetic properties will be discussed (R = Y, Pr, Nd, Sm, Gd, … and T = Fe, Co, Si, Al, Ga, Mo, Zr, Cr, Ti, V, …). The influence of the microstructure on the extrinsic magnetic properties of these R–T based intermetallic nanomaterials, prepared by high energy ball milling followed by short annealing, will be also be shown. In addition, the electronic structure studied by DFT will be presented and compared to the results of experimental magnetic measurements as well as the hyperfine parameter determined by Mössbauer spectrometry. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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17 pages, 7079 KiB

Open AccessReview

Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

by Andrzej Ślebarski and Maciej M. Maśka

Materials 2020, 13(24), 5830; https://doi.org/10.3390/ma13245830 - 21 Dec 2020

Cited by 6 | Viewed by 2073

Abstract

We investigated the effect of enhancement of superconducting transition temperature

T_{c}

by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La

_{3} M_{4}

Sn

_{13}

, Ca

_{3}

Rh

_{4}

Sn

_{13}

, Y

_{5}

Rh

_{6}

Sn

_{18}

[...] Read more.

We investigated the effect of enhancement of superconducting transition temperature

T_{c}

by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La

_{3} M_{4}

Sn

_{13}

, Ca

_{3}

Rh

_{4}

Sn

_{13}

, Y

_{5}

Rh

_{6}

Sn

_{18}

, Lu

_{5}

Rh

_{6}

Sn

_{18}

;

M =

Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale

ξ

in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with

T_{c}^{⋆} > T_{c}

(dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of

T_{c}^{⋆} \sim 2 T_{c}

(dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase

T_{c}^{⋆}

in respect to the bulk

T_{c}

one and proposed a model that explains the

T_{c}^{⋆} > T_{c}

behavior in the series of nonmagnetic skutterudite-related compounds. Full article

(This article belongs to the Special Issue Synthesis, Microstructure and Magnetic Properties of Intermetallic Compounds)

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