Ultrasonic studies of the magnetic phase transition in MnSi

Petrova, A. E.; Стишов, С. М.

doi:10.1088/0953-8984/21/19/196001

Cited by 52 publications

(50 citation statements)

References 20 publications

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“…Meanwhile a careful study of the magnetic phase transition in MnSi confirmed a first order nature of the transition at least at ambient pressure 4,5,6 , as was proposed long ago in Ref.…”

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confidence: 60%

Comment on “Nature of the high-pressure tricritical point in MnSi”

Стишов

2009

Phys. Rev. B

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It is argued that M. Otero-Leal et al. [PRB 79, 060401 (2009) 1 ] wrongly identified the second order term of the Arrott equation with the coefficient at the quartic term of the Landau expansion, therefore deriving absolutely unsupported conclusions on the phase diagram of MnSi.PACS numbers: 75.30. Kz, 75.40.Cx.Despite a long history of extensive studies of the magnetic phase transition in the helimagnet MnSi its phase diagram is not completely understood. Most important but still controversial issues concerning the phase diagram of MnSi are the existence, location and nature of a tricritical point on the phase transition line in MnSi, first suggested in Ref.2 . Since then until recently, the existence of the tricritical point has been never in doubt though its location was disputed in Ref.3 . Meanwhile a careful study of the magnetic phase transition in MnSi confirmed a first order nature of the transition at least at ambient pressure 4,5,6 , as was proposed long ago in Ref.7 . This observation reversed the situation. It was believed before that a second order phase transition in MnSi became first order at high pressure. Then the only conclusion could be made that the phase transition in MnSi turned to second order at high pressure. The latter of course is valid if a tricritical point does exist at the transition line. However new experiments at high pressure using helium as a pressure medium showed that the early claims on the existence of a tricritical point at the phase transition line, based on an analysis of behavior of magnetic susceptibility, are most probably a result of misinterpretation of the experimental data 8 . As was said in Ref.8 :"The new measurements unambiguously show that the striking change of the magnetic susceptibility curve is a result of non-hydrostatic stresses in pressure media and has nothing to do with a change of character of the phase transition in MnSi". So the general conclusion was that the magnetic phase transition in MnSi continued to be first order in the whole pressure range studied 8 . In the paper 1 an attempt was made to resolve the above mentioned issues based, as the authors said, on "a direct analysis of the magnetic phase transition under pressure". Under "a direct analysis" the authors implied applications of the equationwhere H-magnetic field, M -magnetization. Equation(1), suggested by Arrott 9 , is a typical mean field relation and can be readily derived from the Landau expansion 10 . Normally the relation (1) is used to plot H/M vs M 2 (Arrott plot), which would yield a straight line at the temperature of second order ferromagnetic phase transition when the critical fluctuations can be neglected. Eq. (1) needs to be modified to account for the contribution of critical fluctuations (see Ref.11 ). It has to be emphasized that a causal relationship between the Landau expansion and Eq.1 limited to ferromagnetic materials, since only in this case the magnetization M can serve as an order parameter with the magnetic field H as a conjugate variable. Neglecting this i...

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“…Meanwhile a careful study of the magnetic phase transition in MnSi confirmed a first order nature of the transition at least at ambient pressure 4,5,6 , as was proposed long ago in Ref.…”

supporting

confidence: 60%

Comment on “Nature of the high-pressure tricritical point in MnSi”

Стишов

2009

Phys. Rev. B

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“…16(d)], thermal expansion, sound velocity, sound absorption, or resistivity. 8 The condensation of the skyrmionic chiral objects is therefore a major transformation with some characteristics of a phase transition.…”

Section: Discussionmentioning

confidence: 99%

“…6 The magnetic fluctuations lead to an enhanced effective electron mass, a broad specific heat maximum reminiscent of the specific heat of spin liquids, frustrated magnets or spin glasses, 7 and broad features on thermal expansion and ultrasound measurements, which almost completely mask the helical transition. 8 One intriguing feature of MnSi is that magnetic correlations above T C appear not only around the positions in reciprocal space of the helical order, but spread homogeneously over the whole surface of a sphere with radius τ emerging as a powder-diffraction-like ring on the two-dimensional smallangle neutron scattering spectra. 9 If the neutron beam is polarized, the rings reduce to half-moons due to the interaction between polarized neutrons with the helical correlations as explained below.…”

Section: Introductionmentioning

confidence: 99%

Magnetic fluctuations and correlations in MnSi: Evidence for a chiral skyrmion spin liquid phase

et al. 2011

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We present a comprehensive analysis of high-resolution neutron scattering data involving neutron spin echo spectroscopy and spherical polarimetry, which confirm the first-order nature of the helical transition in MnSi. The experiments reveal the existence of a totally chiral dynamic phase in a very narrow temperature range above T C . This unconventional magnetic short-range order has a topology similar to that of a skyrmion liquid or the blue phases of liquid crystals.

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“…The sense of the magnetization rotation is fixed due to the presence of the chiral DzyaloshinskiiMoriya (DM) interaction [20,21]. However, in their magnetic field−temperature, (H, T ), phase diagrams, as sketched in figure 1(a), numerous puzzling physical anomalies have been observed in a narrow temperature interval in the vicinity of T C [8,10,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]. The origin of these "precursor anomalies" (hatched area in figure 1(a)) and notably the magnetic structure of the so-called A phase is a long-standing and intriguing problem in chiral magnetism.…”

Section: Introductionmentioning

confidence: 99%

Confinement of chiral magnetic modulations in the precursor region of FeGe

Wilhelm

Baenitz

Schmidt

et al. 2012

J. Phys.: Condens. Matter

111

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Abstract. We report on magnetic susceptibility and specific heat measurements of the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at T C = 278.2(3) K. Pronounced anomalies in the field-dependent χac(H) data as well as in the corresponding imaginary part χ ac (H) reveal a precursor region around T C in the magnetic phase diagram. The occurrence of a maximum at T 0 = 279.6 K in the zero-field specific heat data indicates a second order transition into a magnetically ordered state. A shoulder evolves above this maximum as a magnetic field is applied. The field dependence of both features coincides with crossover lines from the field-polarized to the paramagnetic state deduced from χac(T ) at constant magnetic fields. The experimental findings are analyzed within the standard Dzyaloshinskii theory for cubic helimagnets. The remarkable multiplicity of modulated precursor states and the complexity of the magnetic phase diagram near the magnetic ordering are explained by the change of the character of solitonic inter-core interactions and the onset of specific confined chiral modulations in this area.

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Ultrasonic studies of the magnetic phase transition in MnSi

Cited by 52 publications

References 20 publications

Comment on “Nature of the high-pressure tricritical point in MnSi”

Comment on “Nature of the high-pressure tricritical point in MnSi”

Magnetic fluctuations and correlations in MnSi: Evidence for a chiral skyrmion spin liquid phase

Confinement of chiral magnetic modulations in the precursor region of FeGe

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