黒江 晴彦

<p>マルチフェロイック物質 Cu_3_Mo_2_O_9_ では W^6+^ イオンを Mo^6+^ イオンがあるサイトに固溶させると、歪んだ四面体磁性鎖に影響を与えず格子系に乱れを導入することができる。我々のグループは、微分磁化の磁場依存性の振る舞いが二つの置換濃度の間で急激に変化する事を報告している。その境界濃度領域での微分磁化の詳細な置換濃度依存性を、今回は報告する。</p>

The effect of pressure is studied on highly Mg-doped CuGeO3, which at ambient pressure shows an antiferromagnetic transition but no spin-Peierls transition. The magnetic susceptibility under pressure was measured; the broad maximum around 60 K shifts to lower temperatures and the spin-Peierls (SP) transition reappears. The temperature-concentration phase diagram at various pressures was constructed and it was found that the SP phase region enlarges with pressure. These results mean that the enhancement of frustration due to nearest-neighbor and next-nearest-neighbor exchange interactions overcomes the effect of interchain interaction, and that the spin-Peierls phase is more stabilized than the paramagnetic or antiferromagnetic phases. In the temperature-pressure-concentration phase diagram, the compositional phase transition between the dimerized-antiferromagnetic phase and the uniform-antiferromagnetic phase is second order at P &gt; 0.2 GPa, but first order at P &lt; 0.2 GPa. We propose that the change in order of this transition is also due to enhancement of the frustration. We show an example of frustration effects in a one-dimensional quantum spin system.