The structural and magnetic properties of the single-molecule magnet [Mn11CrO12(O2CCH3) 16(H2O)4]·2CH3COOH· 4H2O (Mn11Cr) are studied through the analysis of a Mn11Cr/Mn12 (≈1:1) mixed crystal, where Mn12 is [Mn12O12(O2CCH3) 16(H2O)4]·2CH3COOH· 4H2O. X-ray absorption spectra reveal that the Cr ion in Mn 11Cr is in the +3 valence state and occupies a specific Mn 3+ site in the Mn12 skeleton. High-frequency electron paramagnetic resonance (EPR) spectra are well explained by assuming that Mn 11Cr is in a ground spin-state of S=19/2 with nearly the same EPR parameter set as for Mn12. The lower spin quantum number results in lower barrier height (56.8 K) compared to Mn12. The magnetization curves indicate a coercive field of 0.95 T for Mn11Cr at 1.8 K, nearly half that for Mn12. Quantum tunneling of magnetization (QTM) in Mn11Cr is observed below the blocking temperature TB, with the same field interval as for Mn12. The magnetization of Mn11Cr and Mn12 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 Mn12, suggesting the effect of dipolar-biased tunneling.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2004 Sept