Spin Gap State of S = 1/2 Heisenberg Antiferromagnet YbAl_3C_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

概要

論文の詳細を見る
YbAl_3C_3 has been investigated in detail, which was previously reported to show an antiferroquadrupolar (AFQ) ordering at an extremely high ordering temperature of 80K. The present study has revealed that the specific heat, magnetic susceptibility, and electrical resistivity of the single crystalline YbAl_3C_3 clearly exhibit the characteristic features of the first order transition around 77K. In addition, we have discovered that LuAl_3C_3 also exhibits a sharp peak in the specific heat around 110K, which most likely corresponds to the 77K transition of YbAl_3C_3. Therefore, the 77K transition of YbAl_3C_3 is considered to be irrelevant to the nature of the 4f-electrons such as the AFQ ordering but is ascribed to a structural one. Low temperature physical properties of YbAl_3C_3 below 77K is indicative of a spin gap and a nonmagnetic ground state. A new model is proposed, in which the adjacent spins on the triangular lattice of Yb^<3+> ions are antiferromagnetically coupled to form a dimer by the structural transition at 77K. The spin gap behavior at low temperatures can be well explained by an isolated dimer model with a singlet-triplet energy gap of about 15K.
社団法人日本物理学会の論文
2007-12-15