Topological transitions among skyrmion- and hedgehog-lattice states in cubic chiral magnets

Fujishiro, Yukako; Kanazawa, Naoya; Nakajima, Taro; Yu, Xiaojiang; Ohishi, Kazuki; Kawamura, Yukihiko; Kakurai, Kazuhisa; Arima, Taka‐hisa; Mitamura, Hiroyuki; Miyake, Atsushi; Akiba, Kazuto; Tokunaga, Masashi; Matsuo, Akira; Kindo, Koichi; Koretsune, Takashi; Arita, Ryotaro; Tokura, Y.

doi:10.1038/s41467-019-08985-6

Cited by 149 publications

(150 citation statements)

References 47 publications

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“…In addition, in MnSi 1−x Ge x , the 3Q-HL changes into a different HL characterized by tetrahedral four wave vectors, dubbed the quadruple-Q hedgehog lattice (4Q-HL) [ Fig. 1(b)] [14,15]. Remarkably, the magnetic periods of these 3Q-and 4Q-HLs are very short ∼ 2-3 nm, in contrast to most of the skyrmion lattices.Such magnetic HLs have been theoretically studied prior to the experimental discovery, e.g., by the Ginzburg-Landau theory [16], variational calculations [17], and Monte Carlo (MC) simulations [18].…”

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Magnetic hedgehog lattices in noncentrosymmetric metals

et al. 2020

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Magnets with noncentrosymmetric lattice structures can host a three-dimensional noncoplanar spin texture called the magnetic hedgehog lattice (HL) with a periodic array of magnetic monopoles and anti-monopoles. Despite recent discovery of two types of short-period HLs in MnSi1−xGex, their microscopic origin remains elusive. Here, we study the stability of such magnetic HLs for an effective spin model with long-range interactions arising from the itinerant nature of electrons. By variational calculations and simulated annealing, we find that the HLs are stabilized in the ground state at zero magnetic field by the synergetic effect of the antisymmetric exchange interactions generated by the spin-orbit coupling and the multiple-spin interactions generated by the spin-charge coupling. We also clarify the full phase diagram in the magnetic field, which includes multiple phase transitions with changes in the number of monopoles and anti-monopoles.Chirality, often termed as handedness, is a key concept in a broad field of science, ranging from particle physics to biology. In condensed matter physics, chiral magnetic textures, which break both inversion and mirror symmetries in additon to time-reversal symmetry, have recently attracted considerable attention for potential applications to next-generation electronic devices. There are a variety of the chiral magnetic textures, such as skyrmion lattices [1] and chiral soliton lattices [2]. Noncollinear and noncoplanar spin arrangements in these textures generate emergent electromagnetic fields through the Berry phase mechanism, which induce unconventional transport, optical, and magnetoelectric properties [3][4][5].Recently, a three-dimensional chiral magnetic texture, which is called the hedgehog lattice (HL), was discovered in the B20-type compound MnGe [6,7]. The magnetic structure is characterized by cubic three wave vectors, and hence, it is referred as the triple-Q hedgehog lattice (3Q-HL) [ Fig. 1(a)]. The 3Q-HL has a periodic array of hyperbolic hedgehog and anti-hedgehog spin textures, which generates an emergent magnetic field with a periodic array of radial hedgehogs and anti-hedgehogs regarded as magnetic monopoles and anti-monopoles, as shown in Fig. 1(c) [8][9][10]. The peculiar magnetic field was discussed as a source of the enormous topological Hall effect [11] and thermoelectoric effect [12,13]. In addition, in MnSi 1−x Ge x , the 3Q-HL changes into a different HL characterized by tetrahedral four wave vectors, dubbed the quadruple-Q hedgehog lattice (4Q-HL) [ Fig. 1(b)] [14,15]. Remarkably, the magnetic periods of these 3Q-and 4Q-HLs are very short ∼ 2-3 nm, in contrast to most of the skyrmion lattices.Such magnetic HLs have been theoretically studied prior to the experimental discovery, e.g., by the Ginzburg-Landau theory [16], variational calculations [17], and Monte Carlo (MC) simulations [18]. The variational study for a classical spin model showed that the 3Q-HL is not stabilized, whereas the 4Q-HL is obtained in an applied magnetic field [17]. The 4Q...

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Magnetic hedgehog lattices in noncentrosymmetric metals

et al. 2020

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“…It means that the parameter which governs the suppression of the HS-LS transition is not the chemical pressure but most likely the magnetic disorder induced by Co and Rh ions which bear weak magnetic moments, either intrinsic [18] or induced [26]. We note that a rather smooth evolution of the saturated moment was recently reported in MnSi 1−x Ge x , in relation to an ≈5% change of lattice constant [27]. There also, one should account for the effective magnetic contribution of Ge [26] and for the influence of disorder on the band structure to capture the nature of the observed transition.…”

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Suppression of the bulk high spin–low spin transition by doping the chiral magnet MnGe

et al. 2019

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In the MnGe chiral magnet, the helimagnetic order and local moment collapse in two steps, showing the succession of high spin (HS) and low spin (LS) states as pressure increases. Here, we use high-pressure neutron diffraction to study the doped compounds Mn 0.86 Co 0.14 Ge and Mn 0.9 Rh 0.1 Ge, and show that the evolution of their microscopic magnetic properties is instead continuous. It means that the bulk HS-LS transition is a unique feature of pure MnGe, very sensitive to small changes of the band structure and easily suppressed by chemical substitution. On the other hand, the helimagnetic correlations appear to be strengthened by doping and survive up to larger pressures (≈19 GPa, to be compared with ≈13 GPa). We discuss these results in the light of other disordered systems with remarkable properties, the so-called Invar alloys.

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“…In contrast, the other experiment shows that the helical ordering temperature can reach 39 K by replacing only 1% Si with Ge [14]. Quite recently, there appears a report on magnetic properties of MnSi 1−x Ge x in a wide x range 0 ≤ x ≤ 1, using high-pressure synthesis [15]. As this work focuses on the topological transitions in the wide x-range, there are only one or two data points in x < 0.2, and hence it is still unclear how magnetic properties vary in the low-x range.…”

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confidence: 95%

Effect of Ge substitution on magnetic properties in the itinerant chiral magnet MnSi

Aji

Ishida

Okuyama

et al. 2019

Phys. Rev. Materials

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We have investigated the effect of Ge-substitution to the magnetic ordering in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under ambient pressure. From metallurgical survey, the solubility limit of Ge was found to be x = 0.144(5) with annealing temperature Tan = 1073 K. Magnetization measurements on MnSi1−xGex samples show that the helical ordering temperature Tc increases rapidly in the low-x range, whereas it becomes saturated at higher concentration x > 0.1. The Ge substitution also increases both the saturation magnetization Ms and the critical field to the fully polarized state Hc2. In contrast to the saturation behavior of Tc, those parameters increase linearly up to the highest Ge concentration investigated. In the temperature-magnetic field phase diagram, we found enlargement of the skyrmion phase region for large x samples. We, furthermore, observed the non-linear behavior of helical modulation vector k as a function of Ge concentration, which can be described qualitatively using the mean field approximation.

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Topological transitions among skyrmion- and hedgehog-lattice states in cubic chiral magnets

Cited by 149 publications

References 47 publications

Magnetic hedgehog lattices in noncentrosymmetric metals

Magnetic hedgehog lattices in noncentrosymmetric metals

Suppression of the bulk high spin–low spin transition by doping the chiral magnet MnGe

Effect of Ge substitution on magnetic properties in the itinerant chiral magnet MnSi

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