This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn12-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped Mn12-Ac are obtained： （i） MnllCr-Ac （S=19/2, D=0.62K, B=0.0009K, A=63K）, and （ii） Mn11Fe-Ac （S=21/2, D=0.39 K, B=0.001 K, △=55 K）. The single-ion origin of the magnetic anisotropy is discussed.
A new single-molecule magnet [Mn11Fe1O12 （CH3COO）16（H2O）4]·2CH3COOH·4H2O （Mn11Fe1） has been synthesized. The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn-Teller distortion between Fe^3＋ and Mn^3＋ ion reveals that Fe^3＋ ion substitutes for Mn^3＋ ion on the Mn（3） sites in the Mn12 skeleton. The temperature dependence of the magnetization gives a blocking temperature TB=1.9K for Mn11Fe1. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn11Fe1 has the ground state with a total spin S=11/2.
