Abstract
We examine the surface size- and shape-effects of soliton annihilation and soliton nucleation in chiral magnet CrNb3S6. We measure magnetization (M) curves of submillimeter-sized single crystals with an equal length along the c-axis (Lc = 10 μm) but with different cross sections in the ab-plane (Sab = 0.120–0.014 mm2). We find a ferromagnetic type of magnetizing (FMM) with a convex curve (d2M/dH2 < 0) near zero field (H = 0) and a major jump in M near the forced ferromagnetic state, which are more conspicuous, compared with earlier samples with submillimeter Lc [K. Tsuruta et al. J. Phys. Soc. Jpn. 85, 013707 (2016)]. A new finding is that the major jump in M occurs at lower fields in samples with the smaller Sab. We further perform numerical simulation of the magnetization process with the Landau–Lifshitz–Gilbert equation of the Langevin-type. Based on the numerical results, we attribute the FMM at small fields to rapid annihilation of soliton assisted by the reduction of Dzyaloshinskii-Moriya interaction near the surfaces. We also discuss possible penetration processes of chiral soliton through the ac-(bc-)plane as well as ab-plane, and its relation to the major jump in M. Our experimental and calculated results will contribute to understanding of the effects of topological metastability in chiral magnets.
Highlights
An incommensurate noncollinear magnetic order called a chiral soliton lattice (CSL) has attracted much attention.1–3The CSL appears in a mono-axial chiral helimagnet such as hexagonal CrNb3S63,4 and trigonal YbNi3Al9.5–7 The spin texture is based on the helimagnetic spin structure at zero magnetic field, which results from the competition between exchange interaction along scitation.org/journal/adv the chiral helical axis and an antisymmetric Dzyaloshinskii-Moriya (DM) exchange interaction8,9 along the chiral axis
Topological objects are affected by energy barriers, which causes metastability or hysteresis in the process with change in the number of topological defects12
M is normalized with saturation magnetization Ms The overall behavior of D is similar to the behaviors of A-C which exhibited both small ferromagnetic type of magnetizing (FMM) with a convex curve (d2M/dH2 < 0) at around zero field and small hysteresis just below Hc
Summary
An incommensurate noncollinear magnetic order called a chiral soliton lattice (CSL) has attracted much attention.1–3The CSL appears in a mono-axial chiral helimagnet such as hexagonal CrNb3S63,4 and trigonal YbNi3Al9.5–7 The spin texture is based on the helimagnetic spin structure at zero magnetic field, which results from the competition between exchange interaction along scitation.org/journal/adv the chiral helical axis and an antisymmetric Dzyaloshinskii-Moriya (DM) exchange interaction along the chiral axis. An incommensurate noncollinear magnetic order called a chiral soliton lattice (CSL) has attracted much attention.. The kink-type of spin texture, CSL, is stabilized when a DC magnetic field (H) is applied perpendicularly to the chiral helical axis, and it is a kind of long-ranged topological spin texture, along with the skyrmion lattice system.. Field induced evolution from a helimagnetic state to the forced ferromagnetic state via CSL exhibits a characteristic magnetization (M) curve.. Magnetization processes are accompanied by a change in soliton number.. Topological objects are affected by energy barriers, which causes metastability or hysteresis in the process with change in the number of topological defects Topological objects are affected by energy barriers, which causes metastability or hysteresis in the process with change in the number of topological defects (this energy barrier in chiral magnets is related to surface twist, which has been extensively discussed in Refs. 13–19)
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