AI 中文总结
研究非中心对称四方磁体EuRhGe$_3$的磁场诱导磁结构转变，观测到其从螺旋磁态经孤子晶格态、自旋翻转xyz-扇形态，最终到平面xy-扇形态的完整演化序列。
AI 中文摘要
通过共振X射线衍射对非中心对称体心四方磁体EuRhGe$_3$（空间群$I4mm$）的磁结构进行了研究。在奈尔温度$T_{\text{N}}=12$K以下，EuRhGe$_3$呈现螺旋磁有序，其非公度传播矢量为$q=(0, 0, 0.809)$，磁矩位于$ab$平面内，相邻层间的旋转角为$145.8^\text{o}$。当在2K下沿$a$轴施加磁场时，会出现二次谐波$2q$峰，表明圆形螺旋逐渐畸变为螺旋磁孤子晶格态，最终在3.8T下发生锁模转变，形成$q=0.8$的公度结构。在5T的后续相边界以上，螺旋性消失，进入自旋翻转$xyz$-扇形（椭圆锥形）态，此时磁矩主要沿$b$轴振荡，但伴随有小的$c$轴分量；在更高磁场下，系统进入无$c$轴分量的常规平面$xy$-扇形相。EuRhGe$_3$是螺旋磁体的典型实例，展现了理论预测的完整磁场诱导结构序列，从圆形螺旋到自旋翻转$xyz$-扇形（椭圆锥形），最终到平面$xy$-扇形结构。
英文摘要
The magnetic structure of EuRhGe$_3$, a noncentrosymmetric body-centered tetragonal magnet with the space group $I4mm$, has been investigated by resonant X-ray diffraction. Below $T_{\text{N}}=12$ K, EuRhGe$_3$ undergoes a helical magnetic ordering with an incommensurate propagation vector $q=(0, 0, 0.809)$, in which the magnetic moments lie in the $ab$ plane and rotate by a constant turn angle of $145.8^{\circ}$ between adjacent layers. When a magnetic field is applied along the $a$ axis at 2 K, a second-harmonic $2q$ peak develops, indicating that the circular helix is gradually distorted into a helimagnetic soliton-lattice state, which eventually undergoes a lock-in transition to the commensurate structure with $q=0.8$ at 3.8 T. Above the subsequent phase boundary at 5 T, the helicity is lost, and a spin-flop $xyz$-fan (elliptic conical) state is realized, in which the moments oscillate predominantly along the $b$ axis but are accompanied by a small $c$-axis component. At higher fields, the system enters a conventional planar $xy$-fan phase without a $c$-axis component. EuRhGe$_3$ provides a prototypical example of a helimagnet that exhibits a full sequence of field-induced structures, evolving from a circular helix to a spin-flop $xyz$-fan (elliptic conical), and finally to a planar $xy$-fan structure, which has been theoretically predicted.
Comments10 pages, 10 figures, accepted for publication in J. Phys. Soc. Jpn
Journal refJ. Phys. Soc. Jpn. 95, 104705 (2026)
