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

Abstract

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.

Stability of skyrmion textures and the role of thermal fluctuations in cubic helimagnets: A new intermediate phase at low temperature

“…The low lying spectrum of K, however, is well defined in the continuum limit and shows a weak dependence on the cutoff. The 1-loop approximation is valid if the terms of order ξ 3 and higher that are neglected in (12) do not give a large contribution. Since the leading contribution of the cubic term vanishes by symmetry, the contribution of the higher order terms relative to the quadratic terms can be estimated by the ratio…”

“…If the propagation direction is alonĝ z and the magnetic field has components alongx andẑ, the conical helicoid is described by two functions, θ (z) and ψ(z), that were obtained in Refs. [9,11,12]. It is characterized by two parameters, the angle α and the period L. The CH is recovered in the α → 0 limit, while in the limiting case of h z = 0 we have θ = 0 and cos(ψ/2) = sn( √ h x q 0 z/κ), where sn(x) is the Jacobian elliptic function and κ is the ellipticity modulus [13].…”

Spin-current diode with a monoaxial chiral magnet

“…Meanwhile, when the magnetic field is applied perpendicular to the chiral axis, these monoaxial chiral magnets exhibit another chiral spin structure called the chiral soliton lattice 13,[18][19][20][21] . These peculiar magnetic properties have been theoretically studied by using spin-only models in which the itinerant electron degrees of freedom are inte- grated out [22][23][24][25][26] . In addition, peculiar electrical transport and electronic states have been investigated [27][28][29][30][31][32] .…”

Magnetic field dependence of nonlinear magnetic response and tricritical point in the monoaxial chiral helimagnet Cr1/3NbS2

“…According to recent experimental and theoretical studies, the spatially modulated phase is stable in a region above the Curie temperature, T C . [30][31][32] In this region, a tricritical point along the chiral phase line separates the second-order HNL CSL-FFM transition from the first-order linear CSL-PM phase transition.…”