Chiral Soliton Lattice Formation in Monoaxial Helimagnet Yb(Ni1−x_{1-x}Cux_x)3_3Al9_9

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.Comment: 13 pages, 18 figures, accepted for publication in J. Phys. Soc. Jp

Identification of microscopic spin-polarization coupling in the ferroelectric phase of a magnetoelectric multiferroic CuFe1-xAlxO2

We have performed synchrotron radiation X-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2q, where q is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by Arima [T. Arima, J. Phys. Soc. Jpn. 76, 073702 (2007)]. Comparing the experimental results with the calculation results, we found that the origin of the 2q-lattice modulation is not conventional magnetostriction but the variation in the metal-ligand hybridization between the magnetic Fe^3+ ions and ligand O^2- ions. Combining the present results with the results of a previous polarized neutron diffraction study [Nakajima et al., Phys. Rev. B 77 052401 (2008)], we conclude that the microscopic origin of the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand hybridization with spin-orbit coupling.Comment: 11 pages, 9 figures, to be published in Phys. Rev.

Estimation of spin magnetic moment from x-ray magnetic circularly polarized emission

X線磁気円偏光発光を用いて、金属鉄のスピン磁気モーメントを見積もる方法を開発した。この方法では、オージェ電子分光の解析から得られた2p-3d相互作用を利用しているが、その場合にはスピン磁気モーメントが真の値よりも小さく見積もられたため、2p-3d相互作用を正しく推定する方法が重要であることがわかった。The 19th International Conference on Solid Flilms and Surface

Effect of p-d interaction on circularly polarized Kα emission

X線磁気円偏光発光を用いて、金属鉄における2p-3d相互作用を評価する方法を開発した。その結果、これまでに報告されているオージェ電子分光法の結果と対応した値が得られることがわかった。PF研究会「X線分光理論の新展開：構造・電子状態解析から磁性研究まで」 Frontier of theoretical approaches in x-ray spectroscopie