用共振X射线衍射研究单轴手性磁体DyNi PDMATHAAB Ga $_{9}$中螺旋磁有序和铁四极有序之间的竞争
Competition between helimagnetic and ferroquadrupolar orderings in a monoaxial chiral magnet DyNi$_3$Ga$_{9}$ studied by resonant x-ray diffraction
摘要：
用共振X射线衍射研究了稀土单轴手征磁体DyNi $_3$ Ga $_{9}$的连续相变。磁偶极子和电四极自由度所产生的大的角动量的$J=15/2$，在对称和反对称交换相互作用和晶体场各向异性的组合，引起竞争有序相。我们发现，反铁磁耦合Dy矩在$ab$平面形成一个不相称的helmagnetic顺序与$q\sim(0, 0, 0.43)$低于$T_{\text{N}}=10$ K，进一步表现出连续的一阶过渡到相称helmagnetic顺序与$q=(0,0,0.5)$在$T_{\text{N}}^{\;\prime}=9.0$ K，和倾斜的反铁磁顺序与$q=(0,0,0)$在$T_{\text{N}}^{\;\prime\prime}=8.5$ K，都具有大的共存区域。还唯一地确定了DyNi $_3$ Ga $_{9}$的磁螺旋度与晶体手征度的关系。在$T_{\text{N}}^{\;\prime\prime}$下方观察到$(6,0,0)$布拉格峰的分裂，反映了由于铁四极序引起的晶格畸变。在倾斜反铁磁相，自旋翻转转变发生在5 K时，当温度扫描在弱磁场。我们从上述竞争能量的观点讨论这些转变。
英文摘要：
Successive phase transitions in a rare-earth monoaxial chiral magnet DyNi$_3$Ga$_{9}$ have been investigated by resonant x-ray diffraction. Magnetic dipole and electric quadrupole degrees of freedom arising from the large angular moment of $J=15/2$, in combination with the symmetric and antisymmetric exchange interactions and the crystal field anisotropy, give rise to competing ordered phases. We show that the antiferromagnetically coupled Dy moments in the $ab$-plane form an incommensurate helimagnetic order with $q\sim(0, 0, 0.43)$ just below $T_{\text{N}}=10$ K, which further exhibits successive first-order transitions to the commensurate helimagnetic order with $q=(0,0,0.5)$ at $T_{\text{N}}^{\;\prime}=9.0$ K, and to the canted antiferromagnetic order with $q=(0,0,0)$ at $T_{\text{N}}^{\;\prime\prime}=8.5$ K, both with large coexistence regions. The relation of the magnetic helicity and the crystal chirality in DyNi$_3$Ga$_{9}$ is also uniquely determined. Splitting of the $(6,0,0)$ Bragg peak is observed below $T_{\text{N}}^{\;\prime\prime}$, reflecting the lattice distortion due to the ferroquadrupole order. In the canted antiferromagnetic phase, a spin-flop transition takes place at 5 K when the temperature is swept in a weak magnetic field. We discuss these transitions from the viewpoint of competing energies described above.
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