Special Issue "Magnetic Materials and Magnetism"

A special issue of Quantum Beam Science (ISSN 2412-382X).

Deadline for manuscript submissions: closed (30 June 2018).

Special Issue Editors

Dr. Robert Georgii
E-Mail Website1 Website2
Guest Editor
Heinz Maier-Leibnitz Zentrum (MLZ) and physics department, E21 Science Group coordinator, Quantum Phenomena Instrument MIRA, Technische Universität München, Lichtenbergstr.1, 85748 Garching, Germany
Tel. +49-89-289-14986
Interests: structure and dynamics of skyrmions; helical magnets and other incommensurate structures; development for triple axis spectrometer (TAS) and Spin-Echo neutron instruments

Special Issue Information

Dear Colleagues,

Scope: Herewith, we would like to call for scientific contributions to a Special Issue on Magnetic Materials and Magnetism, investigating the state-of-the art of quantum beam methods, including neutron, synchrotron, muon and positron radiation. We envisage original papers and reviews in the core fields of fundamental and applied solid state physics, chemistry and engineering, with extensions into interdisciplinary fields, such as biology and Earth sciences.

Background: Magnetic materials and the study of magnetism play a vast role in modern technology throughout all aspects and fields. There is almost no technology in daily life which does not use magnetism or magnetic devices. They range from the permanent magnet, though to computer storage, superconductors, sensors and actuators, to very special applications in optics, electronics, nuclear spin resonance imaging and calorimetrics. The understanding and characterization of magnetism in materials, such as structures, their transformations, excitations, and coupling are inherent to the development of novel materials and devices at the forefront of science and technology.

Quantum beams play an important role in probing for magnetism on the nuclear, atomic, crystalline, nano- and microstructural scales. Especially, neutron scattering is widely employed for structural and spectroscopic analyses, as the neutron possesses a spin interacting largely with magnetic moments in the crystal structure. All concepts of Bragg diffraction and inelastic neutron scattering are thus applied to magnetism. To a much lesser extent, and using more complex coupling scatter X-rays, supported by brilliant synchrotron sources, resonant X-ray scattering on magnetic electrons can strongly enhance structural and spectroscopic features. Nuclear resonant X-ray spectroscopy plays an advanced role in the determination of hyperfine magnetic and electronic structures. Muon spin relaxation and positron trapping are other valuable methods to characterize local magnetic fields on the atomic scale. Moreover, magnetic electron diffraction and imaging has notably evolved in recent times, and will round up the complementary nature of different quantum beams.

Magnetic structure on an atomic scale has experienced the most fundamental investigations, encompassing spins on the crystal lattice, exchange interactions and ordering, phase transformations, gradual changes with fields and temperature, coupling of spins to the lattice parameter and the break of crystal symmetry, multiferroic coupling, atomic amorphous arrangements, magnetic disorder as spin glass, etc.

Magnetic domains, coupled to the microstructure, play important roles in the macroscopic magnetic properties and behavior and are of interest in this Special Issue.

Spin excitations and spintronics span a vast field of research, rendering essential functional properties to materials—such as the coupling of spins and electrons in superconductivity, mechanisms of magnetoresistance, skyrmions and spin-orbit coupling.

Dynamics and kinetics are related to domain switching, hysteresis effects, spin waves and damping, as well as in the rearrangement of vortices.

Engineering and technology applications on all scales may include data storage devices and read/write heads, opto-magnetic devices, magnetic actuators and shape-memory materials, energy conversion, medical therapy and diagnosis.

Instrumentation using magnetism and magnetic effects to fundamentally understand and build better machines for characterization in quantum beam science. Examples are magnetic neutron optics, spin-flippers, lenses, improved muon spectrometers, field-free spin echo, and functionality.

Quantum beam theories on how the probe, i.e., the neutron, photon, and muon interact with the sample or its environment, spanning from the basics of magnetic scattering theories, dynamical theories, wave equations and quantum mechanical aspects, to hyperfine interactions, interferometry, etc.

The examples listed above only outline an essential part of the contributions sought for this Special Issue on “Magnetic Materials and Magnetism”. With these aspects in mind, the Special Issue will collect original and review papers employing state-of-the-art quantum beams in applied research and for new and novel developments—both in characterization and in materials.

Dr. Robert Georgii

Prof. Dr. Klaus-Dieter Liss
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Quantum Beam Science is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • structural properties
  • bulk crystal lattices
  • thin multi-layers
  • domains and microstructures
  • magnetic and electronic structure
  • phase transformations
  • critical phenomena
  • collective phenomena
  • multiferroics
  • magneto-electric coupling
  • magneto-mechanic coupling
  • spin-orbit coupling
  • excitations
  • spin waves
  • skyrmions
  • frustration
  • spin-glass
  • nuclear spins
  • spin coupling
  • exchange interactions
  • engineering applications
  • bio-medical applications
  • geology and magnetism
  • magnetism in biology
  • data storage
  • functional materials
  • actuators
  • sensors
  • quantum beam particles and interactions

Published Papers (6 papers)

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Research

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Open AccessArticle
Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses
Quantum Beam Sci. 2018, 2(4), 26; https://doi.org/10.3390/qubs2040026 - 28 Nov 2018
Cited by 1
Abstract
Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from [...] Read more.
Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from the paramagnetic phase to the spin glass phase in an Fe-Cr spin glass with a composition of Fe 17.8 Cr 82.2 was studied in detail by means of NRSE. The microstructure was characterised by APT measurements, which show local concentration fluctuations of Fe and Cr on a length scale of 2 to 5 nm, which lead (i) to the coexistence of ferro- and anti-ferromagnetic clusters and (ii) a change of the magnetic properties of the whole sample, even in the spin glass phase, where spins are supposed to be randomly frozen. We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can also be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Open AccessArticle
On the Robustness of the MnSi Magnetic Structure Determined by Muon Spin Rotation
Quantum Beam Sci. 2018, 2(3), 19; https://doi.org/10.3390/qubs2030019 - 19 Sep 2018
Cited by 1
Abstract
Muon spin rotation ( μ SR) spectra recorded for manganese silicide MnSi and interpreted in terms of a quantitative analysis constrained by symmetry arguments were recently published. The magnetic structures of MnSi in zero-field at low temperature and in the conical phase near [...] Read more.
Muon spin rotation ( μ SR) spectra recorded for manganese silicide MnSi and interpreted in terms of a quantitative analysis constrained by symmetry arguments were recently published. The magnetic structures of MnSi in zero-field at low temperature and in the conical phase near the magnetic phase transition were shown to substantially deviate from the expected helical and conical structures. Here, we present material backing the previous results obtained in zero-field. First, from simulations of the field distributions experienced by the muons as a function of relevant parameters, we confirm the uniqueness of the initial interpretation and illustrate the remarkable complementarity of neutron scattering and μ SR for the MnSi magnetic structure determination. Second, we present the result of a μ SR experiment performed on MnSi crystallites grown in a Zn-flux and compare it with the previous data recorded with a crystal obtained from Czochralski pulling. We find the magnetic structure for the two types of crystals to be identical within experimental uncertainties. We finally address the question of a possible muon-induced effect by presenting transverse field μ SR spectra recorded in a wide range of temperature and field intensity. The field distribution parameters perfectly scale with the macroscopic magnetization, ruling out a muon-induced effect. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Open AccessArticle
The Magnetic Phase Transition and Universality Class of h-YMnO3 and h-(Y0.98Eu0.02)MnO3 Under Zero and Applied Pressure
Quantum Beam Sci. 2018, 2(3), 16; https://doi.org/10.3390/qubs2030016 - 31 Aug 2018
Cited by 1
Abstract
We investigated the antiferromagnetic phase transition in the frustrated and multiferroic hexagonal manganites h-YMnO 3 (YMO) and h-(Y 0.98 Eu 0.02 )MnO 3 (YEMO). Elastic neutron scattering was used to study, in detail, the phase transition in YMO and YEMO under [...] Read more.
We investigated the antiferromagnetic phase transition in the frustrated and multiferroic hexagonal manganites h-YMnO 3 (YMO) and h-(Y 0.98 Eu 0.02 )MnO 3 (YEMO). Elastic neutron scattering was used to study, in detail, the phase transition in YMO and YEMO under zero pressure and in YMO under a hydrostatic pressure of 1.5 GPa. Under conditions of zero pressure, we found critical temperatures of T N = 71.3 ( 1 ) K and 72.11 ( 5 ) K and the critical exponent 0.22 ( 2 ) and β = 0.206 ( 3 ) , for YMO and YEMO, respectively. This is in agreement with earlier work by Roessli et al. Under an applied hydrostatic pressure of 1.5 GPa, the ordering temperature increased to T N = 75.2 ( 5 ) K, in agreement with earlier reports, while β was unchanged. Inelastic neutron scattering was used to determine the size of the anisotropy spin wave gap close to the phase transition. From spin wave theory, the gap is expected to close with a critical exponent, β , identical to the order parameter β . Our results indicate that the gap in YEMO indeed closes at T N = 72.4 ( 3 ) K with β = 0.24 ( 2 ) , while the in-pressure gap in YMO closes at 75.2(5) K with an exponent of β = 0.19 ( 3 ) . In addition, the low temperature anisotropy gap was found to have a slightly higher absolute value under pressure. The consistent values obtained for β in the two systems support the likelihood of a new universality class for triangular, frustrated antiferromagnets. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Open AccessArticle
Coherent Resonant Soft X-ray Scattering Study of Magnetic Textures in FeGe
Quantum Beam Sci. 2018, 2(1), 3; https://doi.org/10.3390/qubs2010003 - 19 Jan 2018
Cited by 4
Abstract
Coherent resonant soft X-ray scattering was utilized to examine the magnetic textures in a thin plate of the cubic B20 compound FeGe. Small-angle scattering patterns were measured with controlled temperatures and magnetic fields exhibiting magnetic scattering from a helical texture and skyrmion lattice. [...] Read more.
Coherent resonant soft X-ray scattering was utilized to examine the magnetic textures in a thin plate of the cubic B20 compound FeGe. Small-angle scattering patterns were measured with controlled temperatures and magnetic fields exhibiting magnetic scattering from a helical texture and skyrmion lattice. By measuring the scattering pattern in a saturation magnetic field, magnetic and charge scattering were distinguished and an iterative phase retrieval algorithm was applied to reconstruct the magnetic texture in the real-space. Results of the real-space reconstruction of magnetic texture from two independently measured datasets were used to compare the reliability of the retrieval. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Review

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Open AccessReview
The Helical Magnet MnSi: Skyrmions and Magnons
Quantum Beam Sci. 2019, 3(1), 4; https://doi.org/10.3390/qubs3010004 - 21 Feb 2019
Abstract
Since the late 1970s, MnSi has played a major role in developing the theory of helical magnets in non-centrosymmetric materials showing the Dzyaloshinsky-Moriya interaction (DMI). With a long helimagnetic pitch of 175 Å as compared to the lattice d-spacing of 4.55 Å, it [...] Read more.
Since the late 1970s, MnSi has played a major role in developing the theory of helical magnets in non-centrosymmetric materials showing the Dzyaloshinsky-Moriya interaction (DMI). With a long helimagnetic pitch of 175 Å as compared to the lattice d-spacing of 4.55 Å, it was ideal for performing neutron studies, especially as large single crystals could be grown. A (B-T)-phase diagram was measured, and in these studies, under the application of a field of about 180 mT perpendicular to the scattering vector Q, a so-called A-phase in the B-T phase diagram was found and first interpreted as a re-orientation of the magnetic helix. After the surprising discovery of the skyrmion lattice in the A-phase in 2009, much interest arose due to the rigidity of the skyrmionic lattice, which is only loosely bound to the crystal lattice, and therefore only relatively small current densities can already induce a motion of this lattice. A very interesting approach to even better understand the complex structures in the phase diagram is to measure and model the spin excitations in MnSi. As the helimagnetic state is characterized by a long pitch of about 175 Å, the associated characteristic excitations form a band structure due to Umklapp scattering and can only be observed at very small Q with energies below 1 meV. Similarly, the excitations of the skyrmion lattice are very soft and low-energetic. We investigated the magnons in MnSi in the whole (B,T)-phase diagram starting in the single-k helimagnetic state by applying a small magnetic field, B = 100 mT. This way, the complexity of the magnon spectrum is significantly reduced, allowing for a detailed comparison of the data with theory, resulting in a full theoretical understanding of the spin system of MnSi in all its different magnetic phases. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Open AccessReview
EMuS Muon Facility and Its Application in the Study of Magnetism
Quantum Beam Sci. 2018, 2(4), 23; https://doi.org/10.3390/qubs2040023 - 07 Nov 2018
Cited by 3
Abstract
A muon facility—EMuS (Experimental Muon Source)—at China Spallation Neutron Source (CSNS) has been studied since 2007. CSNS, which is designed to deliver a proton beam power of 100 kW at Phase-I, and will serve multidisciplinary research based on neutron scattering techniques, has just [...] Read more.
A muon facility—EMuS (Experimental Muon Source)—at China Spallation Neutron Source (CSNS) has been studied since 2007. CSNS, which is designed to deliver a proton beam power of 100 kW at Phase-I, and will serve multidisciplinary research based on neutron scattering techniques, has just completed construction, and is ready to open to general users from September 2018. As an additional platform to CSNS, EMuS aims to provide different muon beams for multiple applications, among which, magnetism study by μSR techniques is a core part. By using innovative designs, such as a long target in conical shape situating in superconducting capture solenoids and forward collection method, EMuS can provide very intense muon beams with a proton beam of 5 kW and 1.6 GeV, from surface muons, decay muons, and high momentum muons to slow muons. In this article, the design aspects of EMuS, including general design, target station, muon beamlines, and μSR spectrometer, as well as prospects for applications on magnetism studies, will be reviewed. Full article
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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