Tricritical point and phase diagram based on critical scaling in the monoaxial chiral helimagnet Cr1/3NbS2

Abstract

In this work, the magnetism of the single crystal Cr 1/3 NbS 2 , which exhibits chiral magnetic soliton lattice (CSL) state, is investigated. The magnetization displays strong magnetic anisotropy when the field is applied perpendicularly and parallel to the c-axis in low field region (H < H S , H S is the saturation field). The critical exponents of Cr 1/3 NbS 2 are obtained as β = 0.370(4), γ = 1.380(2), and δ = 4.853(6), which are close to the theoretical prediction of three-dimensional Heisenberg model. Based on the scaling equation and the critical exponents, the H − T phase diagram in the vicinity of the phase transition is constructed, where two critical points are determined.One is a tricritical point which locates at the intersection between the CSL, forced ferromagnetic (FFM), and paramagnetic (PM) states. The other one is a critical point situated at the boundaries between CSL, helimagnetic (HM), and PM states. I. INTRODUCTIONMagnetic materials with chirality have attracted considerable attention due to spintextures such as helimagnetic (HM) structure, conical magnetic ordering, magnetic skyrmion, chiral bobber [1][2][3][4][5]. The chirality with spin-orbital coupling in the crystal structure results in an antisymmetric exchange interaction called the Dzyaloshinskii-Moriya (DM) interaction, which is 1∼2 orders of magnitude weaker than the ferromagnetic coupling [6,7].The competition between the DM interaction with the ferromagnetic coupling causes the appearance of chiral spin-texture [8]. When an external magnetic field is applied above a threshold value, the HM ordering is usually modulated into particle-like spin-texture such as skyrmion, magnetic soliton.Recently, the monoaxial chiral magnet Cr 1/3 NbS 2 becomes prominent due to the chiral magnetic soliton lattice (CSL), which is a type of superlattice structure consist of periodic helical spin texture [9][10][11]. The crystal structure for Cr 1/3 NbS 2 belongs to the space group P 6 3 22 [12,13]. The hexagonal layers in 2H-NbS 2 are intercalated by the Cr ions which are in the trivalent state with localized moments S = 3/2, whereas the electronic conduction originates from an unfilled band of Nb atoms. Due to the strong magnetocrystalline anisotropy and DM interaction, Cr 1/3 NbS 2 displays a ground state of helical magnetic ordering with vector along the c-axis [13,14]. The magnetic sate can be modulated differently through the direction of the applied external field. When H is applied parallel to the c-axis, the HM ordering is polarized to conical ordering, and finally to forced ferromagnetical (FFM) phase. However, when H is applied perpendicularly to the c-axis, the HM structure with 48 nm changes continuously into CSL state, which is well reproduced by the one-dimensional chiral sine-Gordon model [10]. Further increase of H results in a phase transition from an incommensurate CSL to a commensurate FFM state [15]. It has been demonstrated that CSL can be effectively manipulated by magnetic field or current injection, which supplies potential ap...

Critical phenomenon of the layered chiral helimagnetic YbNi3Al9

“…Here, slight asymmetry can be observed from the out-of-plane M (j) curves, which may be due to the irregular shape of the single crystal in this experiment. The magnetization exhibits the maximum and minimum as H ⊥ c and H//c respectively, which are consistent with results of other chiral helimagnetic materials [41,42]. Figure 3(d) displays the magnified M(H) curves in lower field region for H//c.…”

“…Two points of inflection are observed on each m(h) for T<T C , where the one in lower field region is marked as ¢ H 1 and that in higher field region as ¢ H 2 . These points of inflection are indications of field-induced magnetic phase transitions [41][42][43]50]. Similar inflections caused by the CMS transition is also observed in CrNb 3 S 6 .…”

“…Similar inflections caused by the CMS transition is also observed in CrNb 3 S 6 . Thus, the points of inflection in YbNi 3 Al 9 possibly suggest a CMS transition [42].…”

“…As is known, when H ⊥ c, a possible CMS phase may appear by modulation of external field [33,35]. The magnetic steps with loops for H ⊥ c might be correlated to the transition from the possible CMS to forced ferromagnetic state [42,44]. Theoretical calculation has suggested that magnetic loops caused by intrinsic magnetic hysteresis appear in a CMS system due to the surface barrier [44,45].…”

“…The critical behavior of YbNi 3 Al 9 is very different from that of CrNb 3 S 6 also hosting a chiral helimagnetic state. For CrNb 3 S 6 , it belongs to the 3D-Heisenberg model, the magnetic coupling of which is established not only in the ab-plane but also along the c-axis [42].…”