Magnetic Blue Phase in the Chiral Itinerant Magnet MnSi

Hamann, A.; Lamago, D.; Wolf, Th.; Löhneysen, H. v.; Reznik, D.

doi:10.1103/physrevlett.107.037207

Cited by 61 publications

(54 citation statements)

References 32 publications

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confidence: 67%

“…Other studies of the unusual critical behavior in MnSi include recent polarized neutron scattering experiments [4], from which it was proposed that a "skyrmion-liquid" phase exists for a narrow-temperature range (T ∼ 1 K) above T HM . A similar claim was deduced from a Monte Carlo study where an analogy with blue phases in liquid crystals has been established [6].Recently, Cu 2 OSeO 3 was identified as a new compound to display a direct PM to HM transition in zero magnetic field. Cu 2 OSeO 3 crystallizes in the same space group as MnSi (P 213), and has two crystallographically inequivalent Cu sites with a dominant antiferromagnetic interaction between the nearest neighbors [7].…”

supporting

confidence: 65%

“…Several interpretations have been put forward, including skyrmion liquid phase [4], magnetic blue phase [6], chiral fluctuating states [16], and the Brazovskii renormalization scenario [2].…”

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confidence: 99%

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Critical scaling in the cubic helimagnetCu2OSeO3

et al. 2014

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We present a detailed ac susceptibility investigation of the fluctuation regime in the insulating cubic helimagnet Cu 2 OSeO 3 . For magnetic fields μ 0 H 200 mT, and over a wide temperature (T ) range, the system behaves according to the scaling relations characteristic of the classical three-dimensional Heisenberg model. For lower magnetic fields, the scaling is preserved only at higher T and becomes renormalized in a narrow-T range above the transition temperature. Contrary to the well-studied case of MnSi, where the renormalization has been interpreted within the Brazovskii theory, our analysis of the renormalization at H = 0 shows the fluctuation regime in Universality is a concept that lies at the heart of modern physics since it describes the general scaling behavior of widespread physical phenomena within the vicinity of a critical point. In condensed matter physics, universal scaling laws are readily applied to interpret measurements of thermodynamic observables in order to discern the symmetry of the physical properties close to phase transitions. A classic example where these concepts have been extensively tested, both theoretically and experimentally, is the second-order paramagnetic (PM) to ferromagnetic (FM) transition [1]. In general, as the system approaches the critical point, both the size and the number of fluctuations of the relevant order parameter increase. It is also known that if the interactions between the fluctuations are strong enough, this may even alter the order of the phase transition. In a recent comprehensive study, it was proposed [2] that a specific type of renormalization put forward by Brazovskii [3] can be applied to describe the weakly first-order nature of the PM to helimagnetic (HM) transition at zero magnetic field in metallic MnSi [4,5]. In this scenario, the renormalization arises due to the crucial role played by the Dzyaloshinskii-Moriya (DM) interaction which alters the nature of fluctuations close to T HM , and so causes the system to avoid the second-order transition expected within mean field theory. Other studies of the unusual critical behavior in MnSi include recent polarized neutron scattering experiments [4], from which it was proposed that a "skyrmion-liquid" phase exists for a narrow-temperature range (T ∼ 1 K) above T HM . A similar claim was deduced from a Monte Carlo study where an analogy with blue phases in liquid crystals has been established [6].Recently, Cu 2 OSeO 3 was identified as a new compound to display a direct PM to HM transition in zero magnetic field. Cu 2 OSeO 3 crystallizes in the same space group as MnSi (P 213), and has two crystallographically inequivalent Cu sites with a dominant antiferromagnetic interaction between the nearest neighbors [7]. The ratio of Cu ions within the two inequivalent sites is 3:1, giving rise to the formation of the local ferrimagnetic (FiM) 3-up-1-down state [5] which * zivkovic@ifs.hr is then modulated by the DM interaction. Similar as for MnSi, by applying a weak magnetic field close to the ordering tem...

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confidence: 67%

supporting

confidence: 65%

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Critical scaling in the cubic helimagnetCu2OSeO3

et al. 2014

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“…[28,29,33] identifies this behavior with a fluctuation-induced first-order phase transition proposed by Brazovskiȋ [37], where the fluctuations are isotropically strong on a surface of a sphere in momentum space. Earlier papers suggested [35,38,39] that the transition region may be attributed to the appearance of stable skyrmions in the system (even at zero external field), however, these skyrmions do not show long-range order as evidenced by the neutron scattering experiments.…”

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confidence: 97%

Complex magnetic phase diagram and skyrmion lifetime in an ultrathin film from atomistic simulations

Rózsa¹,

Simon²,

Palotás³

et al. 2016

Phys. Rev. B

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We determined the magnetic B − T phase diagram of PdFe bilayer on Ir(111) surface by performing Monte Carlo and spin dynamics simulations based on an effective classical spin model. The parameters of the spin model were determined by ab initio methods. At low temperatures we found three types of ordered phases, while at higher temperatures, below the completely disordered paramagnetic phase, a large region of the phase diagram is associated with a fluctuation-disordered phase. Within the applied model, this state is characterized by the presence of skyrmions with finite lifetime. According to the simulations, this lifetime follows the Arrhenius law as a function of temperature.

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“…Eearly experimental studies of the electrical resistivity Following the discovery of a skyrmion lattice phase in small applied magnetic fields just below T c [16][17][18][19], several authors have argued that the specific heat and susceptibility provide evidence for further complex phases including a skyrmion liquid phase at zero field [20][21][22][23][24]. Most importantly, it has been claimed that the observation of a chiral fraction η ≈ 1 up to at least 1 K above T c in a seminal SNP study in MnSi by Pappas et al [25,26] provides microscopic evidence supporting a skyrmion liquid phase.…”

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confidence: 99%

Critical spin-flip scattering at the helimagnetic transition of MnSi

et al. 2014

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We report spherical neutron polarimetry (SNP) and discuss the spin-flip scattering cross sections as well as the chiral fraction η close to the helimagnetic transition in MnSi. For our study, we have developed a miniaturised SNP device that allows fast data collection when used in small angle scattering geometry with an area detector. Critical spin-flip scattering is found to be governed by chiral paramagnons that soften on a sphere in momentum space. Carefully accounting for the incoherent spin-flip background, we find that the resulting chiral fraction η decreases gradually above the helimagnetic transition reflecting a strongly renormalised chiral correlation length with a temperature dependence in excellent quantitative agreement with the Brazovskii theory for a fluctuation-induced first order transition. It has long been established that B20 transition metal compounds support a well-understood hierarchy of energy scales [1] comprising in decreasing strength ferromagnetic exchange, Dzyaloshinsky-Moriya spin-orbit interactions and, finally, magnetic anisotropies due to higher-order spin-orbit coupling. In turn, zero temperature spontaneous magnetic order in these materials appears essentially ferromagnetic on short distances with a long wave-length homochiral twist on intermediate distances that propagates along directions favoured by the magnetic anisotropies on the largest length scales.In recent years the nature of the associated helimagnetic transition at T c , which makes contact with areas ranging from nuclear matter over quantum Hall physics to soft matter systems, has been the topic of heated scientific controversy since critical helimagnetic spin fluctuations are able to drive the transition first order. However, considerable differences exists as to the proposed character of these fluctuations. Based on a minimal description taking only into account the three scales mentioned above two scenarios may be distinguished. First, according to Bak and Jensen [2] when the magnetic anisotropies are sufficiently strong, anisotropic critical paramagnons develop along the easy axis already at T > T c . Second, in the opposite limit when the magnetic anisotropies are weak, critical spin fluctuations soften isotropically on the surface of a sphere in momentum space giving rise to a fluctuation-driven first order transition in the spirit of a proposal by Brazovskii [3]. In addition, a third and completely different scenario by Rößler, Bogdanov and Pfleiderer [4] has generated great interest, which requires, however, an additional phenomenological parameter beyond the minimal model. In this model the generic formation of a skyrmion liquid phase between the paramagnetic and helimagnetic state is predicted, which implies an additional phase transition at a temperature T sk > T c .Eearly experimental studies of the electrical resistivity Following the discovery of a skyrmion lattice phase in small applied magnetic fields just below T c [16][17][18][19], several authors have argued that the specific heat and suscepti...

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Magnetic Blue Phase in the Chiral Itinerant Magnet MnSi

Cited by 61 publications

References 32 publications

Critical scaling in the cubic helimagnetCu2OSeO3

Critical scaling in the cubic helimagnetCu2OSeO3

Complex magnetic phase diagram and skyrmion lifetime in an ultrathin film from atomistic simulations

Critical spin-flip scattering at the helimagnetic transition of MnSi

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