Frustration-driven magnetic fluctuations as the origin of the low-temperature skyrmion phase in Co7Zn7Mn6

AbstractIn chiral cubic helimagnets, phases of magnetic skyrmions—topologically protected spin whirls—are stabilized by thermal fluctuations over a narrow region directly below the magnetic ordering temperature Tc. Due to often being touted for use in applications, there is a high demand to identify new ways to stabilize equilibrium skyrmion phases far below Tc where they may display an enhanced robustness against external perturbation due to a larger magnetic order parameter. Here, from quantum beam experiments on the chiral magnet Co7Zn7Mn6, we unveil a direct correlation between the stability of its second skyrmion phase-stable far from Tc, and a concomitant enhancement of an underlying magnetic fluctuation rate that is driven by geometric magnetic frustration. The influences of other leading skyrmion stability mechanisms, such as those derived from thermal fluctuations and low T cubic anisotropies, are shown to be weak in this system. We therefore advance the existence of a fundamental mechanism for stabilizing topological skyrmions in Co7Zn7Mn6 chiral magnet that draws upon magnetic frustration as the key ingredient.

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Disordered skyrmion phase stabilized by magnetic frustration in a chiral magnet

Science Advances ◽

10.1126/sciadv.aar7043 ◽

2018 ◽

Vol 4 (9) ◽

pp. eaar7043 ◽

Cited By ~ 32

Author(s):

Kosuke Karube ◽

Jonathan S. White ◽

Daisuke Morikawa ◽

Charles D. Dewhurst ◽

Robert Cubitt ◽

...

Keyword(s):

Magnetic Transition ◽

Thermal Fluctuations ◽

Structure Type ◽

Frustrated Magnetism ◽

Magnetic Transition Temperature ◽

Geometrically Frustrated ◽

New Class ◽

The Stability ◽

Magnetic Skyrmions ◽

Moriya Interaction

Magnetic skyrmions are vortex-like topological spin textures often observed to form a triangular-lattice skyrmion crystal in structurally chiral magnets with the Dzyaloshinskii-Moriya interaction. Recently, β-Mn structure–type Co-Zn-Mn alloys were identified as a new class of chiral magnet to host such skyrmion crystal phases, while β-Mn itself is known as hosting an elemental geometrically frustrated spin liquid. We report the intermediate composition system Co7Zn7Mn6 to be a unique host of two disconnected, thermal-equilibrium topological skyrmion phases; one is a conventional skyrmion crystal phase stabilized by thermal fluctuations and restricted to exist just below the magnetic transition temperature Tc, and the other is a novel three-dimensionally disordered skyrmion phase that is stable well below Tc. The stability of this new disordered skyrmion phase is due to a cooperative interplay between the chiral magnetism with the Dzyaloshinskii-Moriya interaction and the frustrated magnetism inherent to β-Mn.

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Dynamics and stability of skyrmions in a bended nano-beam

New Journal of Physics ◽

10.1088/1367-2630/ac3a82 ◽

2021 ◽

Author(s):

Anruo Zhong ◽

Xiaoming Lan ◽

Yangfan Hu ◽

Biao Wang

Keyword(s):

Energy Cost ◽

High Mobility ◽

Bending Moment ◽

Elastic Fields ◽

Spintronic Devices ◽

Bulk Stress ◽

The Stability ◽

Magnetic Skyrmions ◽

Nontrivial Topology ◽

A Current

Abstract Magnetic skyrmions are attracting much attention due to their nontrivial topology and high mobility to electric current. Nevertheless, suppression of the skyrmion Hall effect and maintaining high velocity of skyrmions with low energy cost are two major challenges concerning skyrmion-based spintronic devices. Here we show theoretically that in a nano-beam suffering appropriate bending moment, both Bloch-type and Néel-type skyrmions move with a vanishing Hall angle under a current density smaller than that required when the bending is absent. Moreover, bending alone can be used to move skyrmions, whose velocity is solved analytically from the Thiele equation. Generally speaking, inhomogeneous elastic fields affect the stability and dynamics of skyrmions, where the local stability is dominantly determined by the local bulk stress. These findings throw new light on how to drive skyrmions straightly with lower energy cost, which is vital for utilizing skyrmions as information carriers.

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Homeostasis and its disruption in the lung microbiome

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00279.2015 ◽

2015 ◽

Vol 309 (10) ◽

pp. L1047-L1055 ◽

Cited By ~ 57

Author(s):

Robert P. Dickson ◽

John R. Erb-Downward ◽

Gary B. Huffnagle

Keyword(s):

Self Regulation ◽

External Perturbation ◽

Explanatory Models ◽

The Past ◽

Disease States ◽

Lung Microbiome ◽

Interkingdom Signaling ◽

The Stability ◽

Host Inflammatory Response ◽

Community Stress

The disciplines of physiology and ecology are united by the shared centrality of the concept of homeostasis: the stability of a complex system via internal mechanisms of self-regulation, resilient to external perturbation. In the past decade, these fields of study have been bridged by the discovery of the lung microbiome. The respiratory tract, long considered sterile, is in fact a dynamic ecosystem of microbiota, intimately associated with the host inflammatory response, altered in disease states. If the microbiome is a “newly discovered organ,” ecology is the language we use to explain how it establishes, maintains, and loses homeostasis. In this essay, we review recent insights into the feedback mechanisms by which the lung microbiome and the host response are regulated in health and dysregulated in acute and chronic lung disease. We propose three explanatory models supported by recent studies: the adapted island model of lung biogeography, nutritional homeostasis at the host-microbiome interface, and interkingdom signaling and the community stress response.

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Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics

MRS Advances ◽

10.1557/adv.2019.43 ◽

2019 ◽

Vol 4 (11-12) ◽

pp. 643-650 ◽

Cited By ~ 1

Author(s):

Richard Brearton ◽

Maciej W. Olszewski ◽

Shilei Zhang ◽

Morten R. Eskildsen ◽

Charles Reichhardt ◽

...

Keyword(s):

Magnetic Field ◽

Field Gradient ◽

Magnetic Field Gradient ◽

Particle Model ◽

Shear Forces ◽

Magnetic Field Profile ◽

Peak Broadening ◽

Diffraction Patterns ◽

The Stability ◽

Magnetic Skyrmions

ABSTRACTMagnetic skyrmions are particle-like, topologically protected magnetization entities that are promising candidates for information carriers in racetrack-memory schemes. The transport of skyrmions in a shift-register-like fashion is crucial for their embodiment in practical devices. Recently, we demonstrated experimentally that chiral skyrmions in Cu2OSeO3 can be effectively manipulated by a magnetic field gradient, leading to a collective rotation of the skyrmion lattice with well-defined dynamics in a radial field gradient. Here, we employ a skyrmion particle model to numerically study the effects of resultant shear forces on the structure of the skyrmion lattice. We demonstrate that anisotropic peak broadening in experimentally observed diffraction patterns can be attributed to extended linear regions in the magnetic field profile. We show that topological (5-7) defects emerge to protect the six-fold symmetry of the lattice under the application of local shear forces, further enhancing the stability of proposed magnetic field driven devices.

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MAGNETIC ORDERING IN QUASICRYSTALS

Modern Physics Letters B ◽

10.1142/s0217984905009390 ◽

2005 ◽

Vol 19 (27) ◽

pp. 1367-1385 ◽

Cited By ~ 7

Author(s):

E. Y. VEDMEDENKO

Keyword(s):

Magnetic Moments ◽

Ground States ◽

Magnetic Ordering ◽

Single Sample ◽

Magnetic Frustration ◽

Two Dimensional ◽

Theoretical Evidence ◽

Quasiperiodic Tilings ◽

Magnetically Ordered

An overview of the theoretical advances in description of the magnetic ordering and its stability in two-dimensional quasiperiodic tilings with strongly localized magnetic moments is presented. It is demonstrated that combination of the magnetic frustration and the quasiperiodic order of atoms leads to noncollinear ground states. An experimental and theoretical evidence for the possibility of coexistence of stable, magnetically ordered subtilings with highly frustrated, glass-like phases in a single sample is given.

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Stiffness in vortex—like structures due to chirality-domains within a coupled helical rare-earth superlattice

Scientific Reports ◽

10.1038/srep19315 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 5

Author(s):

Amitesh Paul

Keyword(s):

Rare Earth ◽

Domain Walls ◽

Topological Defects ◽

Magnetic Ordering ◽

Direct Consequence ◽

Magnetic Vortex ◽

Range Magnetic Order ◽

Wide Range ◽

Out Of Plane ◽

The Stability

Abstract Vortex domain walls poses chirality or ‘handedness’ which can be exploited to act as memory units by changing their polarity with electric field or driving/manupulating the vortex itself by electric currents in multiferroics. Recently, domain walls formed by one dimensional array of vortex—like structures have been theoretically predicted to exist in disordered rare-earth helical magnets with topological defects. Here, in this report, we have used a combination of two rare-earth metals, e.g."Equation missing" superlattice that leads to long range magnetic order despite their competing anisotropies along the out-of-plane (Er) and in-plane (Tb) directions. Probing the vertically correlated magnetic structures by off-specular polarized neutron scattering we confirm the existence of such magnetic vortex—like domains associated with magnetic helical ordering within the Er layers. The vortex—like structures are predicted to have opposite chirality, side—by—side and are fairly unaffected by the introduction of magnetic ordering between the interfacial Tb layers and also with the increase in magnetic field which is a direct consequence of screening of the vorticity in the system due to a helical background. Overall, the stability of these vortices over a wide range of temperatures, fields and interfacial coupling, opens up the opportunity for fundamental chiral spintronics in unconventional systems.

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Spontaneous skyrmionic lattice from anisotropic symmetric exchange in a Ni-halide monolayer

Nature Communications ◽

10.1038/s41467-020-19535-w ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Danila Amoroso ◽

Paolo Barone ◽

Silvia Picozzi

Keyword(s):

Data Storage ◽

First Principles ◽

Short Range ◽

Magnetic Frustration ◽

Two Dimensional ◽

Spin Structures ◽

Long Range Interactions ◽

Magnetic Skyrmions ◽

Chiral Interaction ◽

Inherent Stability

AbstractTopological spin structures, such as magnetic skyrmions, hold great promises for data storage applications, thanks to their inherent stability. In most cases, skyrmions are stabilized by magnetic fields in non-centrosymmetric systems displaying the chiral Dzyaloshinskii-Moriya exchange interaction, while spontaneous skyrmion lattices have been reported in centrosymmetric itinerant magnets with long-range interactions. Here, a spontaneous anti-biskyrmion lattice with unique topology and chirality is predicted in the monolayer of a semiconducting and centrosymmetric metal halide, NiI2. Our first-principles and Monte Carlo simulations reveal that the anisotropies of the short-range symmetric exchange, when combined with magnetic frustration, can lead to an emergent chiral interaction that is responsible for the predicted topological spin structures. The proposed mechanism finds a prototypical manifestation in two-dimensional magnets, thus broadening the class of materials that can host spontaneous skyrmionic states.

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Theory of Itinerant Electron Magnetism, 2nd Edition

10.1093/oso/9780192895639.001.0001 ◽

2021 ◽

Author(s):

Jürgen Kübler

Keyword(s):

Density Functional ◽

Giant Magnetoresistance ◽

Permanent Magnets ◽

Practical Importance ◽

Magnetic Ordering ◽

Weak Ferromagnetism ◽

Large Field ◽

Itinerant Electron ◽

The Many ◽

Magnetic Skyrmions

The book, in the broadest sense, is an application of quantum mechanics and statistical mechanics to the field of magnetism. Under certain well-described conditions, an immensely large number of electrons moving in the solid will collectively produce permanent magnetism. Permanent magnets are of fundamental interest, and magnetic materials are of great practical importance as they provide a large field of technological applications. The physical details describing the many-electron problem of magnetism are presented in this book on the basis of the density-functional approximation. The emphasis is on realistic magnets, for which the equations describing properties of the many-electron problem can only be solved by using computers. The great recent and continuing improvements are, to a very large extent, responsible for the progress in this field. Along with an introduction to the density-functional theory, the book describes representative computational methods and detailed formulas for physical properties of magnets, which include among other things the computation of magnetic ordering temperatures, the giant magnetoresistance, magneto-optical effects, weak ferromagnetism, the anomalous Hall and Nernst effects, and novel quasiparticles, such as Weyl fermions and magnetic skyrmions.

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Effect of Magnetic Ordering on the Stability of Ni–Mn–Ga(–Co–Cu) Alloys Along the Tetragonal Deformation Path

IEEE Transactions on Magnetics ◽

10.1109/tmag.2017.2707527 ◽

2017 ◽

Vol 53 (11) ◽

pp. 1-6 ◽

Cited By ~ 1

Author(s):

Martin Zeleny ◽

Alexei Sozinov ◽

Torbjorn Bjorkman ◽

Ladislav Straka ◽

Oleg Heczko ◽

...

Keyword(s):

Magnetic Ordering ◽

Deformation Path ◽

Cu Alloys ◽

The Stability

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High-Pressure Routes to New Pyrochlores and Novel Magnetism

Inorganics ◽

10.3390/inorganics7040049 ◽

2019 ◽

Vol 7 (4) ◽

pp. 49

Author(s):

Haidong Zhou ◽

Christopher Wiebe

Keyword(s):

Applied Pressure ◽

Chemical Species ◽

Pyrochlore Structure ◽

Magnetic Ordering ◽

Spin Liquid ◽

Ambient Conditions ◽

Synthesis Conditions ◽

Highly Correlated ◽

The Stability ◽

New Compounds

The pyrochlore structure (A2B2O7) has been an object of consistent study by materials scientists largely due to the stability of the cubic lattice with respect to a wide variety of chemical species on the A or B sites. The criterion for stability under ambient conditions is controlled by the ratio of these cations, which is empirically 1.36 < RA/RB < 1.71. However, under applied pressure synthesis conditions, the pyrochlore lattice is stable up to RA/RB ∼ 2.30, opening up possibilities for new compounds. In this review, we will highlight recent work in exploring new rare-earth pyrochlores such as the germanates RE2Ge2O7 and platinates RE2Pt2O7. We highlight recent discoveries made in these pyrochlores such as highly correlated spin ice behavior, spin liquid ground states, and exotic magnetic ordering.

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