Chiral Soliton Lattice Formation in Monoaxial Helimagnet Yb(Ni1−xCux)3Al9

Takeshi Matsumura,Yosuke Kita,Shigeo Ohara,Katsuya Inoue,Yugo Yoshikawa,Koya Kubo,Shinji Michimura,Toshiya Inami,Yusuke Kousaka

doi:10.7566/jpsj.86.124702

Abstract

Helical magnetic structures and its responses to external magnetic fields in Yb(Ni$_x$Cu$_{1-x}$)$_3$Al$_9$, with a chiral crystal structure of the space group $R32$, have been investigated by resonant X-ray diffraction. It is shown that the crystal chirality is reflected to the helicity of the magnetic structure by a one to one relationship, indicating that there exists an antisymmetric exchange interaction mediated via the conduction electrons. When a magnetic field is applied perpendicular to the helical axis ($c$ axis), the second harmonic peak of $(0, 0, 2q)$ develops with increasing the field. The third harmonic peak of $(0, 0, 3q)$ has also been observed for the $x$=0.06 sample. This result provides a strong evidence for the formation of a chiral magnetic soliton lattice state, a periodic array of the chiral twist of spins, which has been suggested by the characteristic magnetization curve. The helical ordering of magnetic octupole moments, accompanying with the magnetic dipole order, has also been detected.

Highlights

Chirality is one of the most fundamental elements of symmetry in nature. It plays an important role in various phenomena ranging from biological functions to the physical properties of inorganic substances.1) In magnetic materials lacking the local inversion center for the two-ion exchange interaction, a spiral magnetic order is often stabilized by the antisymmetric Dzyaloshinskii–Moriya (DM) interaction, giving rise to distinct physical properties.2,3) The simultaneous appearance of electric polarization with the spiral magnetic order is a typical manifestation of such effects.4) In chiral magnetic materials without both inversion and mirror symmetries, a helical magnetic order with a fixed sense of spin rotation can be stabilized
In monoaxial chiral helimagnets such as CrNb3S6, when a magnetic field is applied perpendicular to the helical axis, the helical ground state transforms into a periodic array of incommensurate chiral spin twists, which separates the ferromagnetically aligned commensurate region.10–14) This is a nonlinear order of topological spin structure and is called a chiral soliton lattice (CSL)
We clarified that the helicity of the magnetic structure has a one-to-one relation with the crystal chirality, indicating that an antisymmetric exchange interaction mediated by the conduction electrons exists, i.e., the RKKY mechanism

Summary

Introduction

Chirality is one of the most fundamental elements of symmetry in nature. It plays an important role in various phenomena ranging from biological functions to the physical properties of inorganic substances.1) In magnetic materials lacking the local inversion center for the two-ion exchange interaction, a spiral magnetic order is often stabilized by the antisymmetric Dzyaloshinskii–Moriya (DM) interaction, giving rise to distinct physical properties.2,3) The simultaneous appearance of electric polarization with the spiral magnetic order is a typical manifestation of such effects.4) In chiral magnetic materials without both inversion and mirror symmetries, a helical magnetic order with a fixed sense of spin rotation can be stabilized. In monoaxial chiral helimagnets such as CrNb3S6 (space group P6322), when a magnetic field is applied perpendicular to the helical axis, the helical ground state transforms into a periodic array of incommensurate chiral spin twists, which separates the ferromagnetically aligned commensurate region.10–14) This is a nonlinear order of topological spin structure and is called a chiral soliton lattice (CSL). These materials are expected to provide a new functionality that is operated by tuning the number of skyrmions or solitons in the sample. ). The detailed study of this compound from the viewpoint of its chirality started with the discovery of a characteristic magnetization process that is reminiscent of a CSL state.26) By substituting Ni with Cu, it was discovered that the M(H) curve behaves to that of CrNb3S6,27) in which the CSL state has clearly been identified.12–14)

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