Ferromagnetism on the frustrated lattices

The two-dimensional t-J model of the triangular and kagome lattice is studied by high temperature expansions. The analyses of uniform susceptibility as well as the ground-state energy show strong evidence that ferromagnetic ground state exists in a wide region in the phase diagram with respect to electron density, n, and superexchange coupling, J, which is a different feature from the case of the square lattice. This result means that the low-density region, where the ferromagnetism is understood by Kanamori's mechanism, continues to Nagaoka's ferromagnetism in frustrated lattices. We also find the possibility of partial ferromagnetism in the low-density region of the triangular lattice.