Structure and magnetic properties of the single-molecule magnet [Mn11CrO12(O2CCH3)(16)(H2O)(4)]center dot 2CH(3)COOH center dot 4H(2)O: magnetization manipulation and dipolar-biased tunneling in a Mn11Cr/Mn-12 mixed crystal

The structural and magnetic properties of the single-molecule magnet [Mn11CrO12(O2CCH3)(16)(H2O)(4)].2CH(3)COOH.4H(2)O (Mn11Cr) are studied through the analysis of a Mn11Cr/Mn-12 (approximate to1:1) mixed crystal, where Mn-12 is [Mn12O12(O2CCH3)(16)(H2O)(4)].2CH(3)COOH.4H(2)O. X-ray absorption spectra reveal that the Cr ion in Mn11Cr is in the +3 valence state and occupies a specific Mn3+ site in the Mn-12 skeleton. High-frequency electron paramagnetic resonance (EPR) spectra are well explained by assuming that Mn11Cr is in a ground spin-state of S=19/2 with nearly the same EPR parameter set as for Mn-12. The lower spin quantum number results in lower barrier height (56.8 K) compared to Mn-12. The magnetization curves indicate a coercive field of 0.95 T for Mn11Cr at 1.8 K, nearly half that for Mn-12. Quantum tunneling of magnetization (QTM) in Mn11Cr is observed below the blocking temperature T-B, with the same field interval as for Mn-12. The magnetization of Mn11Cr and Mn-12 in the mixed crystal can be independently manipulated by utilizing the difference between their coercive fields. The resonance fields of QTM in Mn11Cr are significantly affected by the magnetization direction of Mn-12, suggesting the effect of dipolar-biased tunneling.