NEUTRON DIFFRACTION STUDIES OF TWO-DIMENSIONAL HIGH-ORDER MAGNETIC MODULATION IN RRru_2Si_2 (R: Tb, Dy)

（1）DyRu_2Si_2单晶的脉冲中子衍射测量证实，在高温相，磁调制是一维的，Q=（2/900）。另一方面，在中温阶段，在a^*-B^* 倒易平面上观察到许多低对称线和高对称线上的磁性卫星。这是调制不是一维而是二维的证据。磁性卫星的分布由9a×9a×c的磁性晶胞再现，其中角和体心Dy离子由于挫折而有效地顺磁性。此外，在ISIS磁场下的脉冲中子实验，我们明确了四个变磁相在低温下的磁调制。(1)根据丹麦Risoe国家实验室对TbRu_2Si_2的单晶中子衍射研究，我们证实了磁调制是一维的，Q=（3/1300），但建立了中温相（ITP）的调制为13 a × 13 a ×c的磁单胞的二维调制，包括在角和体心位置的两个受抑Tb离子，类似于DyRu_2Si_2的调制。此外，对于低温相，Q= 3/13 1/4 0的a畴和a-b面内略微畸变的ITP畴共存。

(1)DyRu_2Si_2From pulsed-neutron diffraction measurements of single crystal DyRu_2Si_2, we have confirmed that at the high temperature phase the magnetic modulation is one-dimensional with Q=(2/9 0 0). On the other hand, at the intermediate temperature phase many magnetic satellites on low-symmetry lines as well as high-symmetry lines have been observed in the a^*-b^* reciprocal plane. This is the evidence for the modulation being not one-dimensional but two-dimensional. The distribution of the magnetic satellites is reproduced by a magnetic unit cell of 9a×9a×c, in which the corner and the body-centered Dy ions are effectively paramagnetic due to frustration. Furthermore, pulsed-neutron experiments under magnetic fields at the ISIS, we have made clear the magnetic modulation of the four metamagnetic phases at low temperatures .(1) TbRu_2Si_2From single crystal neutron diffraction studies of TbRu_2Si_2 at Risoe National Laboratory, Denmark we have confirmed that the magnetic modulation is one-dimensional with Q=(3/13 0 0), but established the modulation for the intermediate temperature phase (ITP) to be two-dimensional of the magnetic unit cell being 13a×13a×c, including two frustrated Tb ions at the corner and body-centered positions, similar to the modulation of DyRu_2Si_2. Furthermore, for the low temperature phase two domains of a domain with Q=(3/13 1/4 0) and the ITP domain slightly distorted monoclinically in the a-b plane coexist.