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Thermal relaxation and quantum tunneling of the magnetization in Mn_12-acetate

The dependence of the magnetic moment m on the temperature T and the magnetic field H in a synthesized molecular magnet Mn_12-acetate has beeen measured using a SQUID magnetometer. The splitting of zero-field cooled (ZFC) and field coold (FC) m(T) curves below the so called blocking temperature T_B (~3.6K at H=0) was observed. By measuring the time relaxation of m, it was found that it tended to the same value with the same relaxation time (~560 s at 3 K) for both ZFC and FC processes. This indicates spin freezing below T_B and the single molecule process in the explored temperature range (2k<T<4K). The dependence of T_B on applied H was also investigated. The decreasing of T_B with increasing H can be explained in the frame of barrier reduction in the applied field.

Mn_12-acetate; quantum tunneling; magnetic relaxation

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