Creation of skyrmions and antiskyrmions by local heating

Koshibae, Wataru; Nagaosa, Naoto

doi:10.1038/ncomms6148

Cited by 173 publications

(134 citation statements)

References 29 publications

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“…Particle-like magnetic skyrmions with topologically non-trivial spin textures receive continued attention since their creation, stability and annihilation, either individually or in skyrmion lattices (SkLs), raise fundamental questions related to topology in physics [1][2][3]. Moreover, the observations of metastable skyrmions [4,5] and their current-driven dynamics [6,7] inspires new ideas for using skyrmions in data storage and logic devices [8][9][10].…”

Section: Pacs Numbersmentioning

confidence: 99%

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

et al. 2018

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We report small-angle neutron scattering studies of the lacunar spinel GaV4S8, which reveal the long-wavelength magnetic states to be cycloidally modulated. This provides direct support for the formation of Néel-type skyrmions recently claimed to exist in this compound. In striking contrast with all other bulk skyrmion host materials, upon cooling the modulated magnetic states transform into a ferromagnetic state. These results indicate all of the modulated states in GaV4S8, including the skyrmion state, gain their stability from thermal fluctuations, while at lower temperature the ferromagnetic state emerges in accord with the strong easy-axis magnetic anisotropy. In the vicinity of the transition between the ferromagnetic and modulated states, both a phase coexistence and a soliton-like state are also evidenced by our study. PACS numbers:Particle-like magnetic skyrmions with topologically non-trivial spin textures receive continued attention since their creation, stability and annihilation, either individually or in skyrmion lattices (SkLs), raise fundamental questions related to topology in physics [1][2][3]. Moreover, the observations of metastable skyrmions [4,5] and their current-driven dynamics [6,7] inspires new ideas for using skyrmions in data storage and logic devices [8][9][10].The spin texture of a skyrmion can be described by a vector field S=S(cos(Φ(ϕ))sin(Θ(ρ)), sin(Φ(ϕ))sin(Θ(ρ)), cos(Θ(ρ)), where ϕ and ρ are the azimuth and radial spatial coordinates, respectively [8,11]. The non-trivial skyrmion topology is evidenced when its spin pattern is mapped on to a sphere, and the mapping wraps the surface of the sphere entirely. Two parameters classify the skyrmion type: the vorticity m which is a non-zero integer, and the helicity, γ where Φ(ϕ) = mϕ + γ.The bulk cubic chiral helimagnets with B20 structure, like MnSi and FeGe, host whirlpool-like Bloch-type skyrmions described by m=+1 and γ=±π/2 [4,11,12]. In these compounds the competition between a dominant ferromagnetic (FM) exchange and weaker DzyaloshinskiiMoriya interactions (DMIs) stabilize a long-wavelength (∼10-100 nm) helical ground state in zero magnetic field (B). The SkL phase exists under a finite B, where it competes with either a spin-flop conical phase or a field polarized state. Since the SkL is stable typically only over the narrow temperature (T ) range 0.9 ≤ T ≤ T C , where T C is the ordering T , thermal fluctuations are proposed to be crucial for the phase stability [11][12][13].Recently a new bulk SkL phase was reported in the lacunar spinel GaV 4 S 8 (GVS) [14]. At high T , GVS has a rock-salt like structure composed of alternating GaS 4 and V 4 S 4 clusters. The highest-energy unpaired electron of the V 4 S 4 cluster occupies a triply degenerate molecular orbital which drives a cubic (F 43m) to rhombohedral (R3m) Jahn-Teller transition at T JT =42 K [15][16][17][18][19]. Since this phase transition breaks the 4 symmetry [15], four structural domains develop below T JT . Each domain carries an electric polarization along its r...

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Section: Pacs Numbersmentioning

confidence: 99%

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

et al. 2018

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“…The skyrmionhosting insulating magnets offer precious playgrounds for research into several interesting issues such as optical responses and manipulations of skyrmions [122,123,124], skyrmion-based magnonic crystals [125,126], spin currents [127], spin motive forces [128], spin Seebeck effects [119,129] in the skyrmion phases, elastic responses of skyrmions [130], E-field driven motion and manipulations of skyrmions [78,79,131], and critical and dynamical behaviors of phase transitions [132,133,134,135].…”

Section: Summary and Perspectivesmentioning

confidence: 99%

Dynamical magnetoelectric phenomena of multiferroic skyrmions

Mochizuki¹,

Seki²

2015

J. Phys.: Condens. Matter

112

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Abstract. Magnetic skyrmions, vortex-like swirling spin textures characterized by a quantized topological invariant, realized in chiral-lattice magnets are currently attracting intense research interest. In particular, their dynamics under external fields is an issue of vital importance both for fundamental science and for technical application. Whereas observations of magnetic skyrmions had been limited to metallic magnets so far, their realization was discovered also in a chiral-lattice insulating magnet Cu 2 OSeO 3 in 2012. Skyrmions in the insulator turned out to exhibit multiferroic nature with spin-induced ferroelectricity. Strong magnetoelectric coupling between noncollinear skyrmion spins and electric polarizations mediated by relativistic spin-orbit interaction enables us to drive motion and oscillation of magnetic skyrmions by application of electric fields instead of injection of electric currents. Insulating materials also provide an environment suitable for detection of pure spin dynamics through spectroscopic measurements owing to absence of appreciable charge excitations. In this article, we review recent theoretical and experimental studies on multiferroic properties and dynamical magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that multiferroic skyrmions show unique coupled oscillation modes of magnetizations and polarizations, so-called electromagnon excitations, which are both magnetically and electrically active, and interference between the electric and magnetic activation processes leads to peculiar magnetoelectric effects in a microwave frequency regime. Its magnetizations point in all directions wrapping a sphere. (b) Schematic of the vortextype skyrmion discovered in chiral-lattice ferromagnets, which corresponds to a projection of the hedgehog-type skyrmion onto a two-dimensional plane. Its magnetizations also point everywhere wrapping a sphere. (c) Schematic of a skyrmion crystal realized in chiral-lattice ferromagnets under an external magnetic field, in which skyrmions are hexagonally packed to form a triangular lattice. (d) Helical spin structure (or proper screw spin structure) with magnetizations rotating within a plane normal to propagation vector q.

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“…Successful cross-control of material properties has been reported or proposed for various external stimuli, such as electric field (or electric current)123, magnetic field45, light6, and heat7. Among them, heat is a particularly important stimulus since it allows for the manipulation of the state of matter through its ability to alter the free energy landscape of a system and to realize a metastable state, depending on cooling kinetics.…”

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confidence: 99%

Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1−xMnxTe

Kriener

Nakajima

Kikkawa

et al. 2016

Sci Rep

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Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality.

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Creation of skyrmions and antiskyrmions by local heating

Cited by 173 publications

References 29 publications

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

Dynamical magnetoelectric phenomena of multiferroic skyrmions

Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1−xMnxTe

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