Magnetic Field and Pressure Dependence of Small Angle Neutron Scattering in MnSi

Pfleiderer, C.; Reznik, D.; Pintschovius, L.; Haug, J.

doi:10.1103/physrevlett.99.156406

Cited by 26 publications

(28 citation statements)

References 19 publications

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“…The slope of this line corresponds to the relative pressure dependence of the magnetization d m red /dp ≈ −0.02 kbar −1 with m red = m(p)/m(p = 0), as extrapolated for zero field from fields above B c2 [39]. This rate of decrease is also consistent with the decrease of the ordered magnetic moment inferred from SANS [42,43]. The rate of decrease of ∆ρ top xy with increasing pressure hence follows quantitatively the pressure dependence of the spin polarization as expected from Eq.…”

Section: B Comparison With Experimentssupporting

confidence: 77%

Giant generic topological Hall resistivity of MnSi under pressure

et al. 2013

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We report detailed low temperature magnetotransport and magnetization measurements in MnSi under pressures up to $\sim12\,{\rm kbar}$. Tracking the role of sample quality, pressure transmitter, and field and temperature history allows us to link the emergence of a giant topological Hall resistivity $\sim50\,{\rm n\Omega cm}$ to the skyrmion lattice phase at ambient pressure. We show that the remarkably large size of the topological Hall resistivity in the zero-temperature limit must be generic. We discuss various mechanisms which can lead to the much smaller signal at elevated temperatures observed at ambient pressure

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Section: B Comparison With Experimentssupporting

confidence: 77%

Giant generic topological Hall resistivity of MnSi under pressure

et al. 2013

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“…3 [20]. The observation of neutron scattering intensity above p c at a wavelength which corresponds to that of the helical state at low pressures [12,25] implies that the continuous evolution of the topological Hall signal from the A-phase to the NFL regime must be closely connected to an unchanged topological winding number. As a caveat, neutron intensity is observed only in a small region of the NFL regime, whereas the topological Hall signal we report here is seen everywhere.…”

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confidence: 97%

“…For e where the boundaries of the regime of the NFL resistivity are shown as a function of T , B and p.The sign and the magnitude of the topological Hall signal arises from a combination of the strength of the emergent field, given by the topological winding number for the magnetic unit cell; the (local) spin polarization of the conduction electrons; and an average over individual bands taking into account different scattering processes [20]. The observation of neutron scattering intensity above p c at a wavelength which corresponds to that of the helical state at low pressures [12,25] implies that the continuous evolution of the topological Hall signal from the A-phase to the NFL regime must be closely connected to an unchanged topological winding number. As a caveat, neutron intensity is observed only in a small region of the NFL regime, whereas the topological Hall signal we report here is seen everywhere.Thus, the topological winding must be insensitive against fluctuations above p c , at least on time scales relevant to the Hall effect.…”

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confidence: 99%

Formation of a topological non-Fermi liquid in MnSi

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Wagner

et al. 2013

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Here we report a high-pressure study of the metallic state at the border of the skyrmion lattice in MnSi, which represents a new form of magnetic order composed of topologically non-trivial vortices [2]. When long-range magnetic order is suppressed under pressure, the key characteristic of the skyrmion latticethat is, the topological Hall signal due to the emergent magnetic flux associated with their topological winding -is unaffected in sign or magnitude and becomes an important characteristic of the metallic state. The regime of the topological Hall signal in temperature, pressure and magnetic field coincides thereby with the exceptionally extended regime of a pronounced non-Fermi-liquid resistivity [3, 4]. The observation of this topological Hall signal in the regime of the NFL resistivity suggests empirically that spin correlations with non-trivial topological character may drive a breakdown of Fermi liquid theory in pure metals.To address the nature of the metallic state at the border of long-range topological order we have selected the B20 compound MnSi. At zero pressure, p = 0, MnSi undergoes a fluctuation-induced first-order transition to helimagnetic order at T c = 29.5 K [5]. The helimagnetism originates in a hierarchy of three energy scales, comprising ferromagnetic exchange on the strongest scale, Dzyaloshinsky-Moriya interactions on an intermediate scale and higher-order spin-orbit coupling on the weakest scale [6]. As a function of field, B, conical order appears for B > B c1 ≈ 0.1 T, and this is followed by a spin-polarized state for B > B c2 ≈ 0.6 T. A phase pocket in the vicinity of T c , known as the A-phase, supports the skyrmion lattice [2]. The magnetic phase diagram of MnSi including the skyrmion lattice is thereby generic for all helimagnetic B20 compounds, regardless whether they are high-purity metals [2,7], semiconductors [8,9] or insulators [10,11].2 As a function of pressure, the helimagnetic transition in MnSi vanishes above p c ≈ 14.6 kbar without quantum criticality [12][13][14]. Yet the resistivity changes from the T 2 dependence of a Fermi liquid to the T 3/2 dependence of a non-Fermi liquid (NFL) when p exceeds p c . The exceptionally wide NFL range [3, 4] and the lack of sample dependence of the T 3/2 coefficient contrast with the excellent quantitative description of MnSi as a weak itinerant magnet [15], suggesting that the cause of the NFL behaviour may be an intrinsic mechanism mimicking the effects of disorder and glassiness. This notion is supported by neutron scattering, NMR and muon spin resonance measurements, suggesting partial magnetic order on timescales between 10 −10 s and 10 −11 s [12,14]. In turn, several theoretical studies [16][17][18] explored a proliferation of topological spin textures as the cause of the partial order, with a possible link to the NFL resistivity [19]. However, until now, evidence for topologically non-trivial spin textures in the NFL regime as well as a link between such textures and the NFL behaviour has not been reported.A unique experim...

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“…Neutron scattering observed a continuous variation of the helical Bragg peak intensity I B at T = 2 K near p c . 29,30 This, however, cannot be taken as evidence for a second-order quantum transition, since I B ∝ S 2 × V ord is proportional to the product of the square of the ordered moment S and the volume fraction V ord of the ordered region, and neutron studies cannot distinguish between contributions from S and V ord . In the case of MnSi, the continuous variation of I B is due to the discontinuous change of S at p c multiplied by the continuous development of V ord below p = p c .…”

Section: Introductionmentioning

confidence: 99%

Restoration of quantum critical behavior by disorder in pressure-tuned (Mn,Fe)Si

et al. 2017

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In second-order quantum phase transitions from magnetically ordered to paramagnetic states at T = 0, tuned by pressure or chemical substitution, a quantum critical point is expected to appear with critical behavior manifesting in the slowing down of spin fluctuations in the paramagnetic state and a continuous development of the order parameter in the ordered state. Quantum criticality is discussed widely as a possible driving force for unconventional superconductivity and other exotic phenomena in correlated electron systems. In the real world, however, quantum critical points and quantum criticality are often masked by a preceding first-order transition and/or the development of competing states. Pressure tuning of the itinerant-electron helical magnet MnSi is a well-known example of the suppression of a quantum critical point due to a first-order phase transition and resulting destruction of the ordered state. Utilizing muon spin relaxation experiments, here we report that 15% Fe-substituted (Mn,Fe)Si exhibits completely different behavior with pressure tuning, including the restoration of second-order quantum critical behavior and a quantum critical point at p QPC~2 1-23 kbar, which coincides with the T = 0 crossing point of the extrapolated phase boundary line of pure MnSi. This result is quantitatively consistent with the recent theory of itinerant-electron ferromagnets by Sang, Belitz, and Kirkpatrick, who argued that disorder would restore a quantum critical point which is otherwise hidden by a firstorder transition.

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Magnetic Field and Pressure Dependence of Small Angle Neutron Scattering in MnSi

Cited by 26 publications

References 19 publications

Giant generic topological Hall resistivity of MnSi under pressure

Giant generic topological Hall resistivity of MnSi under pressure

Formation of a topological non-Fermi liquid in MnSi

Restoration of quantum critical behavior by disorder in pressure-tuned (Mn,Fe)Si

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