Magnetic Susceptibility of [Pd(dmit)2] Salts:
Frustrated Spin-1/2 Heisenberg Antiferromagnets on Triangular Lattice

(Abstract only; Japanese full text is here.)

by M. Tamura, Jan, 2003

(M. Tamura and R. Kato: J. Phys.: Condensed Matter 14 (2002) L729. )

We have found that the temperature dependence of magnetic susceptibility of a series of [Pd(dmit)2] salts is well explained by the model of the spin-1/2 Heisenberg triangular antiferromagnet. The [Pd(dmit)2] salts studied here are Mott insulators under ambient pressure based on dimeric spin-1/2 radical anions.

It is the first time that a molecular material is identified as this basic frustrated antiferromagnetic model by finite temperature behavior, in spite of the long history of research. This study is not only a discovery of a novel phenomenon but also a demonstration of how we can characterize a frustrated triangular antiferromagnetic system.

The ordinary low dimensional spin-1/2 antiferromagnet without frustration, such as chain (the Bonner-Fisher) model or square lattice one, exhibits a susceptibility maximum near T = J/kB, as a result of the growth of antiferromagnetic correlation with decreasing T. In contrast to this, the susceptibility of the spin-1/2 Heisenberg triangular antiferromagnet, in which antiferromagnetic correlation is suppressed by frustration, exhibits a susceptibility maximum at much lower temperature below T = J/3kB, as predicted by the theory based on the high temperature series expansioniN. Elstner et al.: Phys. Rev. Lett. 71 (1993) 1629.j. We have found this characteristic behavior in our experimental data.

The present results supports the scenario that the metallic state is approached as the degree of the frustration increases. A significant role of frustration in strongly correlating electron systems is thus suggested. We believe this finding will open a door to a new concept in the research of the magnetic/conducting molecular materials.