Neutron diffraction study of the chiral magnet MnGe

Makarova, O. L.; Tsvyashchenko, A. V.; André, G.; Porcher, Florence; Фомичева, Л.Н.; Rey, Nicolás A.; Mirebeau, I.

doi:10.1103/physrevb.85.205205

Cited by 74 publications

(95 citation statements)

References 28 publications

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confidence: 71%

“…Its ordering temperature T N = 170(5) K and ordered Mn moment of about 2μ B [14,17] are well above the values in MnSi (29 K and 0.4μ B ). The chiral order coincides with a small structural distortion [17]. The incommensurate wave vector k = (0,0,ζ ) parallel to a (001) axis levels off at a value of 0.167 below 30 K. It corresponds to the shortest helix pitch in the B20 series (29Å instead of 180Å in MnSi or 700Å in FeGe).…”

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Two-step pressure-induced collapse of magnetic order in the MnGe chiral magnet

et al. 2014

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Two-step pressure-induced collapse of magnetic order in the MnGe chiral magnet

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“…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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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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“…Due to the finite-size constraint in MC simulations we can only tune the helix period discontinuously, and conclude that the period λ = 6 definitely supports the monopole crystal phase even at low temperature. To compare with experiments, we adopt the known lattice constant 4.79 Å for MnGe [25] to translate the period λ = 6 to 2.8 nm, which is slightly smaller than the experimentally determined spiral period of 3 ∼ 6 nm for this material. A search for candidate materials with even shorter helix period will be in favor of realizing the three-dimensional topological phase in a more robust manner.…”

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Formation of a topological monopole lattice and its dynamics in three-dimensional chiral magnets

2016

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Topologically protected swirl of the magnetic texture known as the Skyrmion has become ubiquitous in both metallic and insulating chiral magnets. Meanwhile the existence of its three-dimensional analogue, known as the magnetic monopole, has been suggested by various indirect experimental signatures in MnGe compound. Theoretically, Ginzburg-Landau arguments in favor of the formation of a three-dimensional crystal of monopoles and anti-monopoles have been put forward, however no microscopic model Hamiltonian was shown to support such a phase. Here we present strong numerical evidence from Monte Carlo simulations for the formation of a rock-salt crystal structure of monopoles and anti-monopoles in short-period chiral magnets. Real-time simulation of the spin dynamics suggests there is only one collective mode in the monopole crystal state in the frequency range of several GHz for the material parameters of MnGe.PACS numbers: 12.39. Dc, 75.10.Hk, 75.40.Mg Attempts to view building blocks of nature as topologically protected objects such as knots have been a fascinating feature of modern physical science. The knot theory of atoms advanced by Thomson (Lord Kelvin) [1] was re-incarnated by Skyrme as a topological quantum theory of hadrons in the early 60s [2]. Although the topological interpretation of quantum numbers for elementary particles may not have been universally accepted in subatomic physics, the beauty of the idea has remained well within the physics community and, quite recently, found immense physical realization in several kinds of magnetic materials ranging from B20 metallic magnetic compounds [3][4][5], atomically-thin magnetic layers [6], multiferroic insulators [7], to ferroelectrics [8]. The form of the topological matter, now called the Skyrmion lattice, bears excellent resemblance to the well-known vortex lattice in type-II superconductors [9] and shares the character of two dimensionality, extending its existence in a columnar fashion when the host material in which it is formed is three-dimensional. The topological vortex and Skyrmion lattices have both been observed successfully through the visualization technique of Lorentz microscopy [5,10].In higher dimensions one is granted the exciting opportunity to create, observe, and manipulate topological objects not permitted in lower dimensions. For example in three-dimensional Heisenberg magnets with a local unit magnetization vector n r , localized objects known as monopoles and anti-monopoles with integer topological numbers may be formed. The number characterizing the object's topology isfor an integration domain S , parameterized by (u, v), enclosing the monopole center R. Due to the high energetic cost of creating monopoles in isolation, they must be created in reality as a monopole-anti-monopole (MAM) pair, or as a crystal of such pairs forming a new kind of topological lattice unique to three dimensions. Such possibility was suggested theoretically [11] some time ago following the intriguing discovery of diffuse neutron scattering peaks i...

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Neutron diffraction study of the chiral magnet MnGe

Cited by 74 publications

References 28 publications

Two-step pressure-induced collapse of magnetic order in the MnGe chiral magnet

Two-step pressure-induced collapse of magnetic order in the MnGe chiral magnet

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

Formation of a topological monopole lattice and its dynamics in three-dimensional chiral magnets

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