Magnetism

9 pages, 1595 KiB

Open AccessArticle

Kinetics of Domain Structure in Co/Pt/Co Ultrathin Films with Ferromagnetic Interlayer Exchange Interaction: Dependence on Interlayer Thickness

by Ivan Shashkov, Yuri Kabanov, Oleg Tikhomirov and Vladimir Gornakov

Magnetism 2022, 2(2), 186-194; https://doi.org/10.3390/magnetism2020014 - 16 Jun 2022

Cited by 5 | Viewed by 2116

Abstract

We studied the in-field evolution of the domain structure in ultrathin Co(0.6 nm)/Pt(t)/Co(0.6) nm trilayers with perpendicular magnetic anisotropy for 5 nm < t < 6 nm using polar Kerr microscopy. The critical interlayer thickness t_cr = 5.3 nm was found to [...] Read more.

We studied the in-field evolution of the domain structure in ultrathin Co(0.6 nm)/Pt(t)/Co(0.6) nm trilayers with perpendicular magnetic anisotropy for 5 nm < t < 6 nm using polar Kerr microscopy. The critical interlayer thickness t_cr = 5.3 nm was found to separate two principal patterns of domain behavior including interlayer correlations and motility of the domain walls. It is shown that magnetization in both Co layers is coupled with strong ferromagnetic interaction for small Pt thickness (t < t_cr), while this coupling is weak for thicker (t > t_cr) Pt layers. Nonlinear dependence of the wall displacement on the field value is observed. The established final position of domain walls after relaxation depends on the Pt layer thickness. It is determined by balance of the interlayer exchange and energy gain due to the field. The mechanism of wall stabilization is considered in the case of independent wall motion. In the region with weak coupling, dependence of the interlayer interaction energy on Pt thickness was measured. Full article

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7 pages, 2064 KiB

Open AccessArticle

Synthesis and Physical Properties of NbMnP Single Crystals

by Jianda Zhao, Zhixue Shu, Ranuri S. Dissanayaka Mudiyanselage, Weiwei Xie and Tai Kong

Magnetism 2022, 2(2), 179-185; https://doi.org/10.3390/magnetism2020013 - 7 Jun 2022

Cited by 2 | Viewed by 2273

Abstract

Single crystalline NbMnP was grown by the high-temperature solution growth technique and characterized by room temperature X-ray diffraction, temperature- and field-dependent magnetization, temperature-dependent resistivity, and heat capacity measurements. NbMnP is isostructural to TiNiSi with the space group of Pnma. Physical characterizations suggest that [...] Read more.

Single crystalline NbMnP was grown by the high-temperature solution growth technique and characterized by room temperature X-ray diffraction, temperature- and field-dependent magnetization, temperature-dependent resistivity, and heat capacity measurements. NbMnP is isostructural to TiNiSi with the space group of Pnma. Physical characterizations suggest that NbMnP is metallic and goes through an anti-ferromagnet transition at around 230 K with a weak magnetic anisotropy. A small ferromagnetic component is found to be perpendicular to [010]. Full article

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11 pages, 2016 KiB

Open AccessArticle

Competing Magnetic Interactions in Inverted Zn-Ferrite Thin Films

by Murtaza Bohra, Sai Vittal Battula, Nitesh Singh, Baidyanath Sahu, Anil Annadi and Vidyadhar Singh

Magnetism 2022, 2(2), 168-178; https://doi.org/10.3390/magnetism2020012 - 17 May 2022

Cited by 7 | Viewed by 2699

Abstract

Zn-ferrite is a versatile material among spinels owing to its physicochemical properties, as demonstrated in rich phase diagrams, with several conductive or magnetic behaviors dictated by its cation inversion. The strength and the type of cation inversion can be manipulated through the various [...] Read more.

Zn-ferrite is a versatile material among spinels owing to its physicochemical properties, as demonstrated in rich phase diagrams, with several conductive or magnetic behaviors dictated by its cation inversion. The strength and the type of cation inversion can be manipulated through the various thermal treatment conditions. In this study, inverted Zn-ferrite thin films prepared from radio frequency magnetron sputtering were subjected to different in situ (in vacuum) and ex situ (in air) annealing treatments. The temperature and field dependence of magnetization behaviors reveal multiple magnetic interactions compared to its bulk antiferromagnet behavior. Using the magnetic component model, the different magnetic interactions can be explained in terms of superparamagnetic (SPM), paramagnetic (PM), and ferrimagnetic (FM) contributions. At low temperatures, the SPM and FM contributions can be approximated to the hard and soft ferrimagnetic phases of Zn-ferrite, respectively, which changes with the annealing temperature and sputter power. Distinct magnetic properties emanating from in situ annealing compared to the ex situ annealing were ascribed to the nonzero Fe²⁺/Fe³⁺ ratio, leading to the different magnetic interactions. The anisotropy was found to be the key parameter that governs the behavior of annealed in situ samples. Full article

(This article belongs to the Special Issue Magnetic Surfaces: Thin Films and Nanostructures)

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16 pages, 33221 KiB

Open AccessArticle

Anthropogenic Sources of Electromagnetic Interference in the Lowest ELF Band Recordings (Schumann Resonances)

by Janusz Mlynarczyk, Vasilis Tritakis, Ioannis Contopoulos, Zenon Nieckarz, Vasilis Christofilakis, Georgios Tatsis and Christos Repapis

Magnetism 2022, 2(2), 152-167; https://doi.org/10.3390/magnetism2020011 - 5 May 2022

Cited by 2 | Viewed by 2114

Abstract

Recording systems that deal with Extra Low Frequency (ELF) data in the Schumann resonance (SR) range exhibit high sensitivity to external noise. In our effort to refine a time series by identifying and removing external disturbances from real data, we analyzed the effect [...] Read more.

Recording systems that deal with Extra Low Frequency (ELF) data in the Schumann resonance (SR) range exhibit high sensitivity to external noise. In our effort to refine a time series by identifying and removing external disturbances from real data, we analyzed the effect of induced deliberate anthropogenic disturbances. The signals were recorded at the same time and same place by two separate systems with different designs and implementations. The main purpose of this experiment was to confirm that different systems in various observational sites could identify parasitic noises in the same way. The outcomes of this study may help ELF observers to discern intrinsic signals from artificial noise. Full article

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22 pages, 4862 KiB

Open AccessArticle

Vector-Based Magnetic Circuit Modelling of Induction Motors

by Braden Kidd

Magnetism 2022, 2(2), 130-151; https://doi.org/10.3390/magnetism2020010 - 28 Apr 2022

Cited by 1 | Viewed by 2740

Abstract

Electro-mechanical devices incorporating rotating magnetic fields can be modelled using a wide range of analytical techniques. Choosing a modelling technique usually requires a trade off between computational efficiency and accuracy. Magnetic flux-based models aim to achieve an optimum balance between computational intensity and [...] Read more.

Electro-mechanical devices incorporating rotating magnetic fields can be modelled using a wide range of analytical techniques. Choosing a modelling technique usually requires a trade off between computational efficiency and accuracy. Magnetic flux-based models aim to achieve an optimum balance between computational intensity and accuracy, as required for real time control applications. This paper demonstrates how vector-based magnetic circuit equations can be used to describe the operational characteristics of an induction motor at a more fundamental level than commonly used magnetic flux models. Doing so allows for closed form equations to be derived directly from device-specific geometry. The resultant model has advantages of numerical method-based analytical techniques while retaining the computational efficiency of closed form equations. Full article

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

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13 pages, 2823 KiB

Open AccessArticle

Reflection and Refraction of a Spin at the Edge of a Quasi-Two-Dimensional Semiconductor Layer (Quantum Well) and a Topological Insulator

by Saraswati Shee, Raisa Fabiha, Marc Cahay and Supriyo Bandyopadhyay

Magnetism 2022, 2(2), 117-129; https://doi.org/10.3390/magnetism2020009 - 18 Apr 2022

Cited by 3 | Viewed by 1888

Abstract

We derive the reflection and refraction laws for an electron spin incident from a quasi-two-dimensional semiconductor region (with no spin–orbit interaction) on the metallic surface of a topological insulator (TI) when the two media are in contact edge to edge. For a given [...] Read more.

We derive the reflection and refraction laws for an electron spin incident from a quasi-two-dimensional semiconductor region (with no spin–orbit interaction) on the metallic surface of a topological insulator (TI) when the two media are in contact edge to edge. For a given incident angle, there can generally be two different refraction angles for refraction into the two spin eigenstates in the TI surface, resulting in two different ‘spin refractive indices’ (birefringence) and the possibility of two different critical angles for total internal reflection. We derive expressions for the spin refractive indices and the critical angles, which depend on the incident electron’s energy for given effective masses in the two regions and a given potential discontinuity at the TI/semiconductor interface. For some incident electron energies, there is only one critical angle, in which case 100% spin polarized injection can occur into the TI surface from the semiconductor if the angle of incidence exceeds that critical angle. The amplitudes of reflection of the incident spin with and without spin flip at the interface, as well as the refraction (transmission) amplitudes into the two spin eigenstates in the TI, are derived as functions of the angle of incidence. Full article

(This article belongs to the Special Issue Exclusive Collection: Papers from the Editorial Board Members of Magnetism)

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12 pages, 4478 KiB

Open AccessArticle

Static and Dynamic Magneto-Elastic Sensing Properties of Fe-Al Alloy Powder-Epoxy Composite Patches

by Suok-Min Na, Byungseok Yoo, Darryll J. Pines, Jin-Hyeong Yoo and Nicholas J. Jones

Magnetism 2022, 2(2), 105-116; https://doi.org/10.3390/magnetism2020008 - 1 Apr 2022

Cited by 1 | Viewed by 2011

Abstract

By combining the two types of magnetoelastic and magnetochromatic materials in an epoxy, we can make a hybrid system that exhibits an optical response due to an elastic strain. It could be used in structural health monitoring, for real-time monitoring of crack propagation [...] Read more.

By combining the two types of magnetoelastic and magnetochromatic materials in an epoxy, we can make a hybrid system that exhibits an optical response due to an elastic strain. It could be used in structural health monitoring, for real-time monitoring of crack propagation or general evaluation of the condition of a structure, both visualized by a change in color. In this study, magnetostrictive polymer composites (MPCs) with Fe₈₁Al₁₉ (Alfenol) alloy particles are evaluated to determine magneto-elastic properties in composite patches attached to a surface, prior to understanding the full hybrid magneto–elasto–optical interactions. To measure static magneto-elastic performance, a tension apparatus within a solenoid was fabricated to apply uniform strain to the MPC patch on an aluminum dog-bone substrate. It was demonstrated that, for epoxies with an elastic modulus higher than ~0.1 GPa, a tensile strain/stress applied to the composite improved magneto-elastic coupling, resulting in increased permeability values, at least up to strains of 0.1%. Composites were fabricated with both spherical and flake-shaped powders, with flake-shaped powders exhibiting better magnetic responses than those with spherical morphology. Alfenol MPCs were also measured dynamically at ultrasonic frequencies, exhibiting comparable dynamic sensing performance to Galfenol at 120 kHz using ultrasonic guided wave techniques. Full article

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17 pages, 69597 KiB

Open AccessArticle

Orientation-Dependent Indentation Behaviour of Additively Manufactured FeCo Sample: A Quasi In-Situ Study

by Sudipta Pramanik, Frederik Tasche, Kay-Peter Hoyer and Mirko Schaper

Magnetism 2022, 2(2), 88-104; https://doi.org/10.3390/magnetism2020007 - 25 Mar 2022

Viewed by 1991

Abstract

The quasi in-situ indentation behaviour of <110>||BD and <111>||BD-oriented grains in a FeCo alloy is studied in this investigation. The effect of build height on melt pool shape and melt pool size is also studied by finite element method simulations. As the building [...] Read more.

The quasi in-situ indentation behaviour of <110>||BD and <111>||BD-oriented grains in a FeCo alloy is studied in this investigation. The effect of build height on melt pool shape and melt pool size is also studied by finite element method simulations. As the building height increases, the aspect ratio of the elliptical melt pool increases. Correspondingly, the effect of the laser scan speed on the melt pool shape and size is studied by the finite element method, because, as the laser scan speed increases, the aspect ratio of the elliptical melt pool increases, too. The microstructural characterisation of the indentation area before and after indentation is performed by electron backscatter diffraction (EBSD). Based on the EBSD data grain reference orientation deviation (GROD), calculations are performed to describe the effect of indentations on the neighbouring grain orientations. High GROD angles are detected in the neighbouring grain region adjoining the indented grain. An in-depth slip trace analysis shows the activation of all three slip systems ({110}<111>, {112}<111> and {123}<111>) which is also confirmed by slip lines on the sample surface that are detected by laser scanning confocal microscopy. A high concentration of geometrically necessary dislocations (GNDs) are observed on the adjoining area to the indentation. Local surface topography measurements by laser scanning confocal microscopy confirmed the formation of pile-ups near the indentation. Full article

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Magnetism, Volume 2, Issue 2 (June 2022) – 8 articles

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