Phase transitions and ordering structures of a model of a chiral helimagnet in three dimensions

Nishikawa, Yoshihiko; Hukushima, Koji

doi:10.1103/physrevb.94.064428

Cited by 32 publications

(24 citation statements)

References 35 publications

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“…The results about the phase diagram of the monoaxial helimagnet presented here are compatible with Monte Carlo simulations recently performed [33]. These simulations point out that the zero-field transition is of second order and belongs to the universality class of the XY model and is thus of instability type, while a different kind of transition, which might be a nucleation type second-order transition, takes place when the perpendicular magnetic field is strong enough.…”

Section: Discussionsupporting

confidence: 90%

Understanding theH−Tphase diagram of the monoaxial helimagnet

2016

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Some unexpected features of the phase diagram of the monoaxial helimagnet in presence of an applied magnetic field perpendicular to the chiral axis are theoretically predicted. A rather general Hamiltonian with long-range Heisenberg exchange and Dzyaloshinskii-Moriya interactions is considered. The continuum limit simplifies the free energy, which contains only a few parameters which in principle are determined by the many parameters of the Hamiltonian, although in practice they may be tuned to fit the experiments. The phase diagram contains a chiral soliton lattice phase and a forced ferromagnetic phase separated by a line of phase transitions, which are of second order at low T and of first order in the vicinity of the zero-field ordering temperature, and are separated by a tricritical point. A highly nonlinear chiral soliton lattice, in which many harmonics contribute appreciably to the spatial modulation of the local magnetic moment, develops only below the tricritical temperature, and in this case, the scaling shows a logarithmic behavior similar to that at T = 0, which is a universal feature of the chiral soliton lattice. Below the tricritical temperature, the normalized soliton density curves are found to be independent of T , in agreement with the experimental results of magnetorresistance curves, while above the tricritical temperature they show a noticeable temperature dependence. The implications in the interpretation of experimental results of CrNb 3 S 6 are discussed.

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Section: Discussionsupporting

confidence: 90%

Understanding theH−Tphase diagram of the monoaxial helimagnet

2016

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“…After completing the first version of our manuscript [arXiv1512.00235v2], we come to know an experimental result suggesting a tri-critical point, which is a boundary between the first-and second-order phase transition, at about 40% of H ⊥ c (0) [29]. The change of the order/type of the phase transition along the phase boundary in the magnetic field was also discussed recently by two groups [30,31]. We briefly remark on the order of the transition in our analysis.…”

Section: Discussionmentioning

confidence: 89%

Finite-Temperature Properties of Three-Dimensional Chiral Helimagnets

et al. 2016

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We study a three-dimensional (3d) classical chiral helimagnet at finite temperatures through analysis of a spin Hamiltonian, which is defined on a simple cubic lattice and consists of Heisenberg exchange, mono-axial Dzyaloshinskii-Moriya interactions and Zeeman energy due to magnetic field applied in the plane perpendicular to the helical axis. We take account of quasi-two-dimensionality of a known mono-axial chiral helimagnet CrNb3S6 and we adopt three methods: (i) a conventional mean-field (MF) analysis which we call 3dMF method, (ii) a hybrid method called 2dMC-1dMF, which is composed of a classical Monte Carlo (MC) simulation and MF approximation applied respectively to the intra-and inter-plane interactions, and (iii) a simple-MC simulation (3dMC) at zero field. Temperature dependence of magnetization calculated by the 3dMF method shows a cusp-like structure similar to that observed in experiments. In the absence of magnetic field, both 2dMC-1dMF and 3dMC yield close values of transition temperature. The 2dMC-1dMF provides a quantitative description of thermodynamic properties even under external field at an accessible numerical cost.

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“…The period L 0 is independent of T , but the local magnetic moment decreases with T , and the transition to the PM state takes place at the temperature where it vanishes. The nature of the transition at T 0 is not fully understood and considerable effort is being devoted to clarify this interesting question [9][10][11][12][13][14][15] . At temperatures lower than T 0 , application of a magnetic field perpendicular to the DM axis deforms the helix and a chiral soliton lattice (CSL) appears 6,7,[16][17][18] .…”

Section: Introductionmentioning

confidence: 99%

Nucleation, instability, and discontinuous phase transitions in monoaxial helimagnets with oblique fields

2017

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The phase diagram of the monoaxial chiral helimagnet as a function of temperature (T ) and magnetic field with components perpendicular (Hx) and parallel (Hz) to the chiral axis is theoretically studied via the variational mean field approach in the continuum limit. A phase transition surface in the three dimensional thermodynamic space separates a chiral spatially modulated phase from a homogeneous forced ferromagnetic phase. The phase boundary is divided into three parts: two surfaces of second order transitions of instability and nucleation type, in De Gennes terminology, are separated by a surface of first order transitions. Two lines of tricritical points separate the first order surface from the second order surfaces. The divergence of the period of the modulated state on the nucleation transition surface has the logarithmic behavior typical of a chiral soliton lattice. The specific heat diverges on the nucleation surface as a power law with logarithmic corrections, while it shows a finite discontinuity on the other two surfaces. The soliton density curves are described by a universal function of Hx if the values of T and Hz determine a transition point lying on the nucleation surface; otherwise, they are not universal.

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Phase transitions and ordering structures of a model of a chiral helimagnet in three dimensions

Cited by 32 publications

References 35 publications

Understanding theH−Tphase diagram of the monoaxial helimagnet

Understanding theH−Tphase diagram of the monoaxial helimagnet

Finite-Temperature Properties of Three-Dimensional Chiral Helimagnets

Nucleation, instability, and discontinuous phase transitions in monoaxial helimagnets with oblique fields

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