Magnetic soliton confinement and discretization effects arising from macroscopic coherence in a chiral spin soliton lattice

Abstract

We present how macroscopically coherent ordering within a chiral state can be manifested in the physical properties within the context of an archetypical system-the chiral spin soliton lattice in a monoaxial chiral magnet CrNb 3 S 6. Using magnetotransport measurements and state-of-the-art Lorentz electron microscopy, we demonstrate spin soliton confinement in 1-μm-wide grains with different crystalline chirality and discretized magnetoresistance in 10-μm-wide crystals. Discretization effects are found to be prominent when the system size is reduced to the order of 10 μm along the chiral axis. A consequence that we identify is a robust coherence of the chiral soliton lattice against deformation. The spin configuration at the grain boundaries, which leads to soliton confinement, is experimentally clarified.

Controlling the Topological Sector of Magnetic Solitons in Exfoliated Cr1/3NbS2 Crystals

“…For these crystals, hysteresis in the magneto-resistance upon reversing the sweeping direction of the applied field is always present, and is accompanied by sharp jumps. The phenomena cannot originate from magnetic domains, since all crystals are significantly thinner than the domain size [22]. We find that the number of jumps tends to increase with increasing the crystal thickness, seemingly correlating with the number of complete periods present in the magnetic helix at B = 0 (determined by t/L 0 where L 0 is the helix pitch).…”

“…Some of these phenomena have been observed recently in small specimen (10 µm in linear dimensions) cut from bulk crystals, in which confinement originates from the presence of magnetic domains extending for approximately 1 µm in the helix direction [22]. Upon increasing B, the separation between solitons increases, so that their total number in each finite-size domain decreases.…”

“…The model enables the spin configuration to be determined through the minimization of the system energy expressed as a functional of the local magnetization. Its validity for Cr 1/3 NbS 2 has been established by direct comparison with Lorentz microscopy experiments and magnetization measurements, which enable the model parameters to be extracted quantitatively [12,22]. The model has also been applied to strained MnSi thinfilms [28,29] [30] to interpret magneto-transport data closely related to the ones discussed here.…”

“…We produced these crystals, up to 500 times thinner than the specimen studied in Ref. [22], by means of mechanical exfoliation, following the same procedure used to extract graphene from graphite. Exfoliation is more difficult for Cr 1/3 NbS 2 because of strong chemical bonds between the Cr and S atoms ; nevertheless, atomic force microscope images (see Figs.…”

“…Since the number of solitons corresponds to the total spin winding number that is a topological index, the soliton number can only change through discrete transitions. These transitions have been detected by analyzing Lorentz microscope images [22]. It was argued that hysteresis and a sequence of jumps present in the magneto-resistance of small specimen, but absent in bulk crystals (see Fig.…”