Magnetism

19 pages, 6136 KiB

Open AccessFeature PaperArticle

Extension of the Application Range of Multipolar Bonded Ring Magnets by Thermosets in Comparison to Thermoplastics

by Uta Rösel and Dietmar Drummer

Magnetism 2023, 3(1), 71-89; https://doi.org/10.3390/magnetism3010007 - 20 Mar 2023

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To expand the range of applications of multipolar bonded magnets based on a thermoplastic matrix, the chemical and thermal resistance has to be increased and the reduced orientation in the rapid solidified surface layer has to be overcome. To meet these requirements, the [...] Read more.

To expand the range of applications of multipolar bonded magnets based on a thermoplastic matrix, the chemical and thermal resistance has to be increased and the reduced orientation in the rapid solidified surface layer has to be overcome. To meet these requirements, the matrix of multipolar bonded magnets can be based on thermosets. This paper investigates in the magnetic properties, especially in the orientation of hard magnetic fillers, the pole accuracy and the mechanical properties of multipolar bonded ring magnets based on the hard magnetic filler strontium-ferrite-oxide and compares the possibilities of thermoplastic (polyamide)- and thermoset (epoxy resin, phenolic resin)-based matrices. It was shown that the magnetic potential of the thermoset-based material can only be fully used with further magnetization. However, the magnetic properties can be increased using thermoset-based compounds compared to thermoplastics in multipolar bonded ring magnets. Further, a model of the orientation and pole accuracy is found in terms of thermoset-based multipolar magnets. In addition, the change of the mechanical properties due to the different matrix systems was shown, with an increase in E-Modulus, E_t, and a reduction in tensile strength, σ_m, and elongation at break, ε_m, in terms of thermosets compared to thermoplastics. Full article

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10 pages, 2959 KiB

Open AccessArticle

Micromagnetics of Microwave-Assisted Switching in Co-Pt-Based Nanostructures: Switching Time Minimization

by Christos Thanos and Ioannis Panagiotopoulos

Magnetism 2023, 3(1), 61-70; https://doi.org/10.3390/magnetism3010006 - 08 Mar 2023

Cited by 1 | Viewed by 1112

Abstract

Microwave-assisted switching (MAS) is simulated for different CoPt and CoPt/Co₃Pt nanosrtuctures as a function of applied DC field and microwave frequency. In all the cases, the existence of microwave excitation can lower the switching field by more than 50%. However, this [...] Read more.

Microwave-assisted switching (MAS) is simulated for different CoPt and CoPt/Co₃Pt nanosrtuctures as a function of applied DC field and microwave frequency. In all the cases, the existence of microwave excitation can lower the switching field by more than 50%. However, this coercivity reduction comes at a cost in the required switching time. The optimal frequencies follow the trends of the ferromagnetic resonances predicted by the Kittel relations. This implies that: (a) when the DC field is applied along the easy axis, the coercivity reduction is proportional to the microwave frequency, whereas (b) when the coercivity is lowered by applying the DC field at an angle of 45° to the easy axis, extra MAS reduction requires the use of high frequencies. Full article

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16 pages, 3476 KiB

Open AccessArticle

Off-Diagonal Magnetoimpedance in Annealed Amorphous Microwires with Positive Magnetostriction: Effect of External Stresses

by Nikita A. Buznikov

Magnetism 2023, 3(1), 45-60; https://doi.org/10.3390/magnetism3010005 - 13 Feb 2023

Cited by 1 | Viewed by 1353

Abstract

It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amorphous microwires with positive magnetostriction can be improved significantly by means of post-annealing. The increase in the GMI is attributed to the induced helical magnetic anisotropy in the surface layer [...] Read more.

It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amorphous microwires with positive magnetostriction can be improved significantly by means of post-annealing. The increase in the GMI is attributed to the induced helical magnetic anisotropy in the surface layer of the microwire, which appears after the annealing. The application of external stresses to the microwire may result in changes in its magnetic structure and affect the GMI response. In this work, we study theoretically the influence of the tensile and torsional stresses on the off-diagonal magnetoimpedance in annealed amorphous microwires with positive magnetostriction. The static magnetization distribution is analyzed in terms of the core–shell magnetic structure. The surface impedance tensor is obtained taking into account the magnetoelastic anisotropy induced by the external stresses. It is shown that the off-diagonal magnetoimpedance response exhibits strong sensitivity to the magnitude of the applied stress. The obtained results may be useful for sensor applications of amorphous microwires. Full article

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11 pages, 5961 KiB

Open AccessArticle

Simulations of Temperature-Dependent Magnetization in Fe_xGd_100−x (20 ≤ x ≤ 80) Alloys

by Oleksandr Pastukh, Dominika Kuźma and Svitlana Pastukh

Magnetism 2023, 3(1), 34-44; https://doi.org/10.3390/magnetism3010004 - 23 Jan 2023

Cited by 2 | Viewed by 2270

Abstract

Theoretical calculations of the temperature-dependent magnetization in FeGd alloys were done with the use of Heisenberg-type atomistic spin Hamiltonian and Monte Carlo algorithms. The random allocation of atoms in the desired crystal structure was used for simulations of magnetically amorphous alloys. Performed calculations [...] Read more.

Theoretical calculations of the temperature-dependent magnetization in FeGd alloys were done with the use of Heisenberg-type atomistic spin Hamiltonian and Monte Carlo algorithms. The random allocation of atoms in the desired crystal structure was used for simulations of magnetically amorphous alloys. Performed calculations for the two different crystal structures have shown an important role of coordination number on the observed critical temperature and compensation point. Moreover, the value of the exchange interaction between Fe and Gd sublattices plays a key role in the simulations—an increase in the Fe–Gd exchange constant provides an increase in critical temperature for each concentration of elements, which explains the higher temperature stabilization of Gd moments. It was shown that obtained temperature-dependent magnetization behavior is consistent with experimental observations, which confirms the applicability of the atomic model used to study FeGd or other magnetic alloy structures. Full article

(This article belongs to the Special Issue Magnetism and Magnetic Properties of Amorphous Alloys)

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2 pages, 143 KiB

Open AccessEditorial

Acknowledgment to the Reviewers of Magnetism in 2022

by Magnetism Editorial Office

Magnetism 2023, 3(1), 32-33; https://doi.org/10.3390/magnetism3010003 - 17 Jan 2023

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Abstract

High-quality academic publishing is built on rigorous peer review [...] Full article

21 pages, 4200 KiB

Open AccessArticle

Numerically Stable and Computationally Efficient Expression for the Magnetic Field of a Current Loop

by Michael Ortner, Peter Leitner and Florian Slanovc

Magnetism 2023, 3(1), 11-31; https://doi.org/10.3390/magnetism3010002 - 30 Dec 2022

Viewed by 2018

Abstract

In this work, it is demonstrated that straightforward implementations of the well-known textbook expressions of the off-axis magnetic field of a current loop are numerically unstable in a large region of interest. Specifically, close to the axis of symmetry and at large distances [...] Read more.

In this work, it is demonstrated that straightforward implementations of the well-known textbook expressions of the off-axis magnetic field of a current loop are numerically unstable in a large region of interest. Specifically, close to the axis of symmetry and at large distances from the loop, complete loss of accuracy happens surprisingly fast. The origin of the instability is catastrophic numerical cancellation, which cannot be avoided with algebraic transformations. All exact expressions found in the literature exhibit similar instabilities. We propose a novel exact analytic expression, based on Bulirsch’s complete elliptic integral, which is numerically stable (15–16 significant figures in 64 bit floating point arithmetic) everywhere. Several field approximation methods (dipole, Taylor expansions, Binomial series) are studied in comparison with respect to accuracy, numerical stability and computation performance. In addition to its accuracy and global validity, the proposed method outperforms the classical solution, and even most approximation schemes in terms of computational efficiency. Full article

(This article belongs to the Special Issue Mathematical Modelling and Physical Applications of Magnetic Systems)

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10 pages, 565 KiB

Open AccessArticle

Correlation of Light Polarization in the Magnetic Media with Non-Spherical Point-Like Inclusions

by Ramil A. Niyazov, Venu Gopal Achanta and Vladimir I. Belotelov

Magnetism 2023, 3(1), 1-10; https://doi.org/10.3390/magnetism3010001 - 29 Dec 2022

Viewed by 1237

Abstract

Light propagation through magnetic media with ellipsoidal inclusions much smaller than the light wavelength was investigated theoretically. It is assumed that the ellipsoidal inclusions have the same orientation but are randomly distributed inside the magnetic medium by the Gaussian law. The theoretical model [...] Read more.

Light propagation through magnetic media with ellipsoidal inclusions much smaller than the light wavelength was investigated theoretically. It is assumed that the ellipsoidal inclusions have the same orientation but are randomly distributed inside the magnetic medium by the Gaussian law. The theoretical model is based on the multiple-scattering theory in the ladder approximation. A new type of electromagnetic field correlation is found to appear in this case, while it is absent in isotropic magnetic nanocomposites and nonmagnetic anisotropic composites. This feature allows for the precise control of light polarization in anisotropic magnetic media. Full article

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Magnetism, Volume 3, Issue 1 (March 2023) – 7 articles

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