High-field magnetization and high-frequency ESR study on the tetranuclear cluster composed of pi-electrons (S=1/2) and d-electrons (S=5/2)

Recently, Iwamura's group has succeeded in synthesizing the interesting new tetranuclear cluster composed of two paramagnetic Mn2+ ions (S=5/2 per ion ) and two organic free radicals (S=1/2 per radical) as bridging ligand, [{M n(hfac)(2)}(2)(bnn)] (bnn=2,2'-bis[( 1-oxyl-3-oxide-4,4,5,5-tetramethyl-imi dazolinyl)]). The crystal structure is triclinic (space group PI) and each cluster is composed of two triangles which share their own base like a "but terfly". There are two kind of exchange pathways within the cluster and bot h of them are likely to be antiferromagnetic. Therefore, spin frustration m ay occur and we expect many possible ground states with different total spi ns (S-T=0 to S-T=6), depending on the relevant interactions and magnetic fi eld. We wish to discuss the important magnetic parameters such as exchange inter actions and anisotropy which characterize this interesting system through m easurements of high-field magnetization and high-frequency electron spin re sonance.