scholarly journals Stabilizing Zero-Field Skyrmions at Room-Temperature in Perpendicularly Magnetized Multilayers

2021 ◽  
Author(s):  
Jeovani Brandão ◽  
Marcos Vinicius Puydinger dos Santos ◽  
Fanny Béron
Keyword(s):  
Room Temperature ◽  
Perpendicular Magnetic Anisotropy ◽  
Electrical Current ◽  
Magnetic Memory ◽  
Zero Field ◽  
Multilayer Systems ◽  
Spin Structures ◽  
Magnetization Saturation ◽  
Out Of Plane ◽  
Magnetic Skyrmions

Magnetic skyrmions are twirling spin structures observed in bulk, thin films, and multilayers with several features for both fundamental physics understanding and spintronic applications, i.e., nanoscale size, efficient transport under electrical current, and topological protection against defects. However, most magnetic skyrmions have been observed under the assistance of an out-of-plane magnetic field, which may limit their use in magnetic memory technologies. In this chapter, we review and present two recent mechanisms to create zero-field skyrmions at room-temperature in ferromagnetic multilayers. First, by tuning the perpendicular magnetic anisotropy (PMA) and remnant magnetization (near magnetization saturation) in unpatterned symmetric multilayer systems, it was achieved a transition from worm-like domains to isolated skyrmions. Besides, we present how to find stable zero-field skyrmions in arrays of ferrimagnetic discs by tailoring their diameter. Both methods demonstrate a robust route to stabilize zero-field skyrmions at room temperature, thus providing an important contribution to possible applications of these textures in the next generation of skyrmionics devices.

Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings

2007 ◽  
Vol 1026 ◽  
Author(s):  
Takeshi Kasama ◽  
Rafal E. Dunin-Borkowski ◽  
Michael R. Scheinfein ◽  
Steven L. Tripp ◽  
Jie Liu ◽  
...  
Keyword(s):  
Room Temperature ◽  
Phase Image ◽  
Objective Lens ◽  
Electron Holography ◽  
Zero Field ◽  
Transmission Electron ◽  
Out Of Plane ◽  
Self Assembled ◽  
Magnetic States

AbstractWe use off-axis electron holography in the transmission electron microscope (TEM) to study magnetic flux closure (FC) states in self-assembled nanoparticle rings that each contain between five and eleven 25-nm-diameter Co crystals. Electron holograms are acquired at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the TEM by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift are determined by turning the samples over, and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent magnetic states, and occasionally onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe.

scholarly journals Microwave resonances of magnetic skyrmions in thin film multilayers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Bhartendu Satywali ◽  
Volodymyr P. Kravchuk ◽  
Liqing Pan ◽  
M. Raju ◽  
Shikun He ◽  
...  
Keyword(s):  
Room Temperature ◽  
Dipolar Coupling ◽  
Dynamic Properties ◽  
Ferromagnetic Layer ◽  
Layer Spacing ◽  
Micromagnetic Simulations ◽  
Out Of Plane ◽  
New Material ◽  
Magnetic Skyrmions ◽  
Spin Resonances

AbstractNon-collinear magnets exhibit a rich array of dynamic properties at microwave frequencies. They can host nanometre-scale topological textures known as skyrmions, whose spin resonances are expected to be highly sensitive to their local magnetic environment. Here, we report a magnetic resonance study of an [Ir/Fe/Co/Pt] multilayer hosting Néel skyrmions at room temperature. Experiments reveal two distinct resonances of the skyrmion phase during in-plane ac excitation, with frequencies between 6–12 GHz. Complementary micromagnetic simulations indicate that the net magnetic dipole moment rotates counterclockwise (CCW) during both resonances. The magnon probability distribution for the lower-frequency resonance is localised within isolated skyrmions, unlike the higher-frequency mode which principally originates from areas between skyrmions. However, the properties of both modes depend sensitively on the out-of-plane dipolar coupling, which is controlled via the ferromagnetic layer spacing in our heterostructures. The gyrations of stable isolated skyrmions reported in this room temperature study encourage the development of new material platforms and applications based on skyrmion resonances. Moreover, our material architecture enables the resonance spectra to be tuned, thus extending the functionality of such applications over a broadband frequency range.

scholarly journals Creation and observation of Hopfions in magnetic multilayer systems

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Noah Kent ◽  
Neal Reynolds ◽  
David Raftrey ◽  
Ian T. G. Campbell ◽  
Selven Virasawmy ◽  
...  
Keyword(s):  
Magnetic Circular Dichroism ◽  
Three Dimensional ◽  
Perpendicular Magnetic Anisotropy ◽  
Theoretical Models ◽  
Magnetic Multilayer ◽  
Multilayer Systems ◽  
Transmission Microscopy ◽  
X Ray ◽  
Three Dimensional Objects ◽  
Magnetic Skyrmions

AbstractAmong topological solitons, magnetic skyrmions are two-dimensional particle-like objects with a continuous winding of the magnetization, and magnetic Hopfions are three-dimensional objects that can be formed from a closed loop of twisted skyrmion strings. Theoretical models suggest that magnetic Hopfions can be stabilized in frustrated or chiral magnetic systems, and target skymions can be transformed into Hopfions by adapting their perpendicular magnetic anisotropy, but their experimental verification has been elusive so far. Here, we present an experimental study of magnetic Hopfions that are created in Ir/Co/Pt multilayers shaped into nanoscale disks, known to host target skyrmions. To characterize three-dimensional spin textures that distinguish Hopfions from target skyrmions magnetic images are recorded with surface-sensitive X-ray photoemission electron microscopy and bulk-sensitive soft X-ray transmission microscopy using element-specific X-ray magnetic circular dichroism effects as magnetic contrast. These results could stimulate further investigations of Hopfions and their potential application in three-dimensional spintronics devices.

scholarly journals Visibility and Apparent Size of Néel-Type Magnetic Skyrmions in Fresnel Defocus Images of Multilayer Films

2021 ◽  
pp. 1-10
Author(s):  
Thibaud Denneulin ◽  
Jan Caron ◽  
Knut Müller-Caspary ◽  
Olivier Boulle ◽  
András Kovács ◽  
...  
Keyword(s):  
Multilayer Structure ◽  
Room Temperature ◽  
Signal To Noise Ratio ◽  
Apparent Size ◽  
Magnetic Signal ◽  
Small Component ◽  
Transmission Electron ◽  
Out Of Plane ◽  
Lorentz Transmission Electron Microscopy ◽  
Magnetic Skyrmions

Multilayers that comprise thin films of heavy metals and ferromagnets have been shown to host Néel-type magnetic skyrmions at room temperature. Fresnel defocus imaging in Lorentz transmission electron microscopy is a widely used technique for recording magnetic information about skyrmions. However, the visibility of Néel-type skyrmions in Fresnel defocus images is typically low, both because only a small component of their magnetic field contributes to the signal and because of the presence of diffraction contrast from the polycrystalline multilayer structure. Here, we take advantage of the out-of-plane hysteresis in such samples to record background-subtracted Fresnel defocus images. We demonstrate an improvement in magnetic signal-to-noise ratio and spatial resolution by a factor of 3 for a (Pt/Co/NiFe)×5 multilayer. We also use simulated Fresnel defocus images of Néel-type magnetic skyrmions to understand the influence of defocus on apparent skyrmion size.

scholarly journals Deriving the skyrmion Hall angle from skyrmion lattice dynamics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
R. Brearton ◽  
L. A. Turnbull ◽  
J. A. T. Verezhak ◽  
G. Balakrishnan ◽  
P. D. Hatton ◽  
...  
Keyword(s):  
High Efficiency ◽  
Magnetic Field Gradient ◽  
Real Space ◽  
Magnetic Multilayer ◽  
Multilayer Systems ◽  
Space Technique ◽  
Hall Angle ◽  
Lattice State ◽  
The Many ◽  
Magnetic Skyrmions

AbstractMagnetic skyrmions are topologically non-trivial, swirling magnetization textures that form lattices in helimagnetic materials. These magnetic nanoparticles show promise as high efficiency next-generation information carriers, with dynamics that are governed by their topology. Among the many unusual properties of skyrmions is the tendency of their direction of motion to deviate from that of a driving force; the angle by which they diverge is a materials constant, known as the skyrmion Hall angle. In magnetic multilayer systems, where skyrmions often appear individually, not arranging themselves in a lattice, this deflection angle can be easily measured by tracing the real space motion of individual skyrmions. Here we describe a reciprocal space technique which can be used to determine the skyrmion Hall angle in the skyrmion lattice state, leveraging the properties of the skyrmion lattice under a shear drive. We demonstrate this procedure to yield a quantitative measurement of the skyrmion Hall angle in the room-temperature skyrmion system FeGe, shearing the skyrmion lattice with the magnetic field gradient generated by a single turn Oersted wire.

The EPR Zero-Field Splitting D and its Pressure and Temperature Dependence for Trigonal Mn2+ Centers in [Zn(H2O)6](BF4)2:Mn2+ Crystal

2006 ◽  
Vol 61 (5-6) ◽  
pp. 289-292 ◽  
Author(s):  
Hong-Gang Liu ◽  
Xiao-Xuan Wu ◽  
Wen-Chen Zheng ◽  
Lv He
Keyword(s):  
Temperature Dependence ◽  
Room Temperature ◽  
Coupling Mechanism ◽  
Zero Field ◽  
Spin Orbit Coupling ◽  
Zero Field Splitting ◽  
Field Splitting ◽  
Thermal Expansion Coefficients ◽  
Perturbation Formula ◽  
Expansion Coefficients

The EPR zero-field splitting D (= b02 ) and its pressure and temperature dependence for trigonal Mn2+ centers in low and room temperature phases in [Zn(H2O)6](BF4)2 :Mn2+ crystal are studied by a high-order perturbation formula based on the dominant spin-orbit coupling mechanism. From the studies, the local trigonal distortion angles, the local angular compressibilities and the local angular thermal expansion coefficients for Mn2+ centers in both phases of the [Zn(H2O)6](BF4)2 crystal are estimated. The results are discussed

scholarly journals Magnetic memory based on magnetic alignment of a paramagnetic ionic liquid near room temperature

2011 ◽  
Vol 47 (15) ◽  
pp. 4475 ◽  
Author(s):  
Yusuke Funasako ◽  
Tomoyuki Mochida ◽  
Takashi Inagaki ◽  
Takahiro Sakurai ◽  
Hitoshi Ohta ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Room Temperature ◽  
Magnetic Alignment ◽  
Magnetic Memory

scholarly journals Origin of perpendicular magnetic anisotropy in amorphous thin films

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Daniel Lordan ◽  
Guannan Wei ◽  
Paul McCloskey ◽  
Cian O’Mathuna ◽  
Ansar Masood
Keyword(s):  
Thin Films ◽  
Magnetic Anisotropy ◽  
Perpendicular Magnetic Anisotropy ◽  
Functional Materials ◽  
Spin Reorientation ◽  
Amorphous Films ◽  
Amorphous Thin Films ◽  
Magnetic Performance ◽  
Out Of Plane ◽  
Sputtering Pressure

AbstractThe emergence of perpendicular magnetic anisotropy (PMA) in amorphous thin films, which eventually transforms the magnetic spins form an in-plane to the out-of-plane configuration, also known as a spin-reorientation transition (SRT), is a fundamental roadblock to attain the high flux concentration advantage of these functional materials for broadband applications. The present work is focused on unfolding the origin of PMA in amorphous thin films deposited by magnetron sputtering. The amorphous films were deposited under a broad range of sputtering pressure (1.6–6.2 mTorr), and its effect on the thin film growth mechanisms was correlated to the static global magnetic behaviours, magnetic domain structure, and dynamic magnetic performance. The films deposited under low-pressure revealed a dominant in-plane uniaxial anisotropy along with an emerging, however feeble, perpendicular component, which eventually evolved as a dominant PMA when deposited under high-pressure sputtering. This change in the nature of anisotropy redefined the orientation of spins from in-plane to out-of-plane. The SRT in amorphous films was attributed to the dramatic change in the growth mechanism of disorder atomic structure from a homogeneously dispersed to a porous columnar microstructure. We suggest the origin of PMA is associated with the columnar growth of the amorphous films, which can be eluded by a careful selection of a deposition pressure regime to avoid its detrimental effect on the soft magnetic performance. To the author’s best knowledge, no such report links the sputtering pressure as a governing mechanism of perpendicular magnetisation in technologically important amorphous thin films.

scholarly journals Ultrathin perpendicular magnetic anisotropy CoFeB free layers for highly efficient, high speed writing in spin-transfer-torque magnetic random access memory

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jodi M. Iwata-Harms ◽  
Guenole Jan ◽  
Santiago Serrano-Guisan ◽  
Luc Thomas ◽  
Huanlong Liu ◽  
...  
Keyword(s):  
Magnetic Anisotropy ◽  
High Speed ◽  
Random Access ◽  
Perpendicular Magnetic Anisotropy ◽  
Spin Transfer Torque ◽  
Tunnel Barrier ◽  
Magnetic Memory ◽  
Material System ◽  
Highly Efficient ◽  
Memory Applications

AbstractPerpendicular magnetic anisotropy (PMA) ferromagnetic CoFeB with dual MgO interfaces is an attractive material system for realizing magnetic memory applications that require highly efficient, high speed current-induced magnetic switching. Using this structure, a sub-nanometer CoFeB layer has the potential to simultaneously exhibit efficient, high speed switching in accordance with the conservation of spin angular momentum, and high thermal stability owing to the enhanced interfacial PMA that arises from the two CoFeB-MgO interfaces. However, the difficulty in attaining PMA in ultrathin CoFeB layers has imposed the use of thicker CoFeB layers which are incompatible with high speed requirements. In this work, we succeeded in depositing a functional CoFeB layer as thin as five monolayers between two MgO interfaces using magnetron sputtering. Remarkably, the insertion of Mg within the CoFeB gave rise to an ultrathin CoFeB layer with large anisotropy, high saturation magnetization, and good annealing stability to temperatures upwards of 400 °C. When combined with a low resistance-area product MgO tunnel barrier, ultrathin CoFeB magnetic tunnel junctions (MTJs) demonstrate switching voltages below 500 mV at speeds as fast as 1 ns in 30 nm devices, thus opening a new realm of high speed and highly efficient nonvolatile memory applications.

scholarly journals Strain-induced perpendicular magnetic anisotropy and Gilbert damping of Tm3Fe5O12 thin films

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Oana Ciubotariu ◽  
Anna Semisalova ◽  
Kilian Lenz ◽  
Manfred Albrecht
Keyword(s):  
Film Thickness ◽  
Magnetic Anisotropy ◽  
Tensile Strain ◽  
Easy Axis ◽  
Perpendicular Magnetic Anisotropy ◽  
Gilbert Damping ◽  
Sample Plane ◽  
Iron Garnets ◽  
Out Of Plane ◽  
Magnetic Easy Axis

AbstractIn the attempt of implementing iron garnets with perpendicular magnetic anisotropy (PMA) in spintronics, the attention turned towards strain-grown iron garnets. One candidate is Tm3Fe5O12 (TmIG) which possesses an out-of-plane magnetic easy axis when grown under tensile strain. In this study, the effect of film thickness on the structural and magnetic properties of TmIG films including magnetic anisotropy, saturation magnetization, and Gilbert damping is investigated. TmIG films with thicknesses between 20 and 300 nm are epitaxially grown by pulsed laser deposition on substituted-Gd3Ga5O12(111) substrates. Structural characterization shows that films thinner than 200 nm show in-plane tensile strain, thus exhibiting PMA due to strain-induced magnetoelastic anisotropy. However, with increasing film thickness a relaxation of the unit cell is observed resulting in the rotation of the magnetic easy axis towards the sample plane due to the dominant shape anisotropy. Furthermore, the Gilbert damping parameter is found to be in the range of 0.02 ± 0.005.

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