Intrinsic instability of the helix spin structure in MnGe and order-disorder phase transition

Altynbaev, E. V.; Siegfried, S.-A.; Dyadkin, Vadim; Moskvin, E. V.; Menzel, D.; Heinemann, A.; Dewhurst, C. D.; Фомичева, Л.Н.; Tsvyashchenko, A. V.; Grigoriev, S. V.

doi:10.1103/physrevb.90.174420

Cited by 25 publications

(39 citation statements)

References 22 publications

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“…The experiment has been performed on the PA20 instrument (Laboratoire Léon Brillouin, France [25]). Helimagnetic correlations are observed as a peak in the structure factor S(Q) at a finite momentum transfer Q h , in agreement with previous neutron-diffraction studies [10,11,18,26]. Data analysis is carried out using a normalized Lorentzian scattering function,…”

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confidence: 84%

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Partial ordering and phase elasticity in the MnGe short-period helimagnet

et al. 2019

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We study the helimagnetic ground state of the MnGe cubic alloy using small-angle neutron scattering and a high-resolution method, the so-called MIEZE spectroscopy. Upon cooling below the Néel temperature T N = 170(5) K, we observe the proliferation of long-wavelength gapless spin fluctuations, concomitant with a continuous evolution of the helical correlation length. These fluctuations disappear at T com = 32(5) K when the helical period becomes commensurate with the lattice. We propose to describe this intermediate phase as a soliton lattice, promoting nonlinear collective modes, or phasons, over a large temperature interval. We discuss the possible relevance of our results to the previously observed magnetotransport anomalies.

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confidence: 84%

“…Below T com , ξ h saturates at ≈ 550 Å, close to the resolution limit. The fact that MnGe does not fully order below T N strongly suggests the existence of peculiar spin fluctuations [26].…”

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confidence: 99%

Partial ordering and phase elasticity in the MnGe short-period helimagnet

et al. 2019

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“…It indicates the correlation between two coexisting fractions. As was shown in [19], the thermal phase transition transition in the MnGe compound is different from already known from Si-based B20 compounds. Its scenario is far from being of the second order.…”

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confidence: 73%

“…The same mechanism as in [10] is applied to explain the hidden QPT in Mn 1−x Fe x Ge. The Mn 1−x Fe x Ge solid solution demonstrates intriguing magnetic properties [13][14][15][16][17][18][19][20][21]. It was recently shown that the helix chirality is altered by mixing the two types of magnetic atoms (Fe and Mn) on the Fe-rich side of the phase diagram [13,18].…”

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confidence: 99%

Hidden quantum phase transition in Mn1−xFexGe evidenced by small-angle neutron scattering

et al. 2016

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The magnetic system of the Mn1−xFexGe solid solution is ordered in a spiral spin structure in the whole concentration range of x ∈ [0 ÷ 1]. The close inspection of the small-angle neutron scattering data reveals the quantum phase transition from the long-range ordered (LRO) to short range ordered (SRO) helical structure upon increase of Fe-concentration at x ∈ [0.25 ÷ 0.4]. The SRO of the helical structure is identified as a Lorentzian contribution, while LRO is associated with the Gaussian contribution into the scattering profile function. The scenario of the quantum phase transition with x as a driving parameter is similar to the thermal phase transition in pure MnGe. The quantum nature of the SRO is proved by the temperature independent correlation length of the helical structure at low and intermediate temperature ranges with remarkable decrease above certain temperature TQ. We suggest the x-dependent modification of the effective RudermanKittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism to explain the quantum critical regime in Mn1−xFexGe. The cubic B20-type compounds (MnSi, etc) are well known for the incommensurate magnetic structures with a very long period appeared due to noncentrosymmetric arrangement of magnetic atoms. It is widely recognized that the helix spin structure is built on the hierarchy of interactions: ferromagnetic exchange interaction, antisymmetric Dzyaloshinskii-Moryia interaction (DMI), and the anisotropic exchange interaction [1,2]. It is also known that the substitution of manganese by iron in the isostructural solid solutions Mn 1−x Fe x Si suppresses the helical spin state [3]. The neutron scattering studies [4,5] together with magnetic data and specific heat measurements [3,6,7] discovered a quantum critical point (QCP) corresponding to the suppression of the spin spiral phase with long-range order (LRO) in Mn 1−x Fe x Si. This QCP located at x c1 ≈ 0.11 − 0.12 is, however, hidden by a short-range order of the spin helix (SRO) [5][6][7] that agrees well with the theoretical models [8,9]. This SRO phase, sometimes referred as chiral spin liquid [8], which is destroyed at the second QCP x c2 ≈ 0.24. Thus it has been shown that Mn 1−x Fe x Si undergoes a sequence of the two quantum phase transitions [7].The real breakthrough in understanding of the experimental facts mentioned above has been done via scrutinizing the Hall effect in Mn 1−x Fe x Si [10]. It was found that the substitution of Mn with Fe results rather in the hole doping opposite to the natural expectations on the electron doping. The two groups of the charge carriers contribute to the Hall effect and the ratio between them changes the sign of the Hall effect constants at x c1 ≈ 0.11, what is definitely associated with the QCP in these compounds. Despite the fact that the solid solutions of Mn 1−x Fe x Si are often considered as itinerant magnets [8,9], recent magnetic resonance and magnetoresistance studies [11,12] favor the alternative explanation based on the Heisenberg localized magn...

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“…In particular, while suggestions for three-dimensional archetypes are scarce, a cubic lattice of topological spin hedgehogs and anti-hedgehogs [ Fig.1(c)] formed from a superposition of three orthogonal helices was recently proposed for the chiral-magnet MnGe [16], and directly observed by Lorentz transmission electron microscopy (LTEM) [33]. The latter study provides an important perspective towards resolving the long-standing controversy on the magnetic structure in MnGe from various neutron diffraction studies [34][35][36][37].…”

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confidence: 97%

Topological spin-hedgehog crystals of a chiral magnet as engineered with magnetic anisotropy

et al. 2017

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We report the engineering of spin-hedgehog crystals in thin films of the chiral magnet MnGe by tailoring the magnetic anisotropy. As evidenced by neutron scattering on films with different thicknesses and with varying magnetic field, we can realize continuously deformable spin-hedgehog crystals, each of which is described as a superposition state of a different set of three spin spirals (a triple-q state). The directions of the three propagation vectors q vary systematically, gathering from the three orthogonal 100 directions towards the film normal as the strength of the uniaxial magnetic anisotropy and/or the magnetic field applied along the film normal increase. The formation of triple-q states coincides with the onset of topological Hall signals, which is ascribed to skew scattering by emergent magnetic field originating in the non-trivial topology of spin hedgehogs.These findings highlight how nano-engineering of chiral magnets makes possible the rational design of unique topological spin textures. 72.15.Gd

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Intrinsic instability of the helix spin structure in MnGe and order-disorder phase transition

Cited by 25 publications

References 22 publications

Partial ordering and phase elasticity in the MnGe short-period helimagnet

Partial ordering and phase elasticity in the MnGe short-period helimagnet

Hidden quantum phase transition in Mn1−xFexGe evidenced by small-angle neutron scattering

Topological spin-hedgehog crystals of a chiral magnet as engineered with magnetic anisotropy

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