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Classical and quantum magnetic relaxation in single molecule magnet Mn12

One of the most famous single molecule magnets is Mn12(-acetate), in which the Mn cations are coupled into the magnetic unit of spin 10. Besides the high magnetic anisotropy, the crystal composed of these non-interacting uniformly oriented magnetic molecules showed the hysteresis loop with steps. These steps were explained by the thermally assisted/activated quantum tunneling of spin. At certain magnetic fields the relaxation becomes much faster, showing the resonant character of tunneling. The relaxation curve measured if quantum tunneling is present seems different from thermal exponential relaxation. Besides classical decreasing of blocking temperature in applied magnetic field, also the local minima at the resonant field appear. After zero-field cooling the dependences of magnetic moment on temperature measured in the resonant fields are different than out of the resonance. All these differences become more pronounced if the transversal magnetic field is applied. Still mysterious question is about the origin of the tunneling. Among many different explanations of the provided inner transversal field are those with hiperfine fields and dislocations in the crystal. This poster will give an overwiev of these facts originating from the combination of the classical and quantum magnetic relaxation of Mn12 toward the equilibrium.

Mn12-acetate; spin tunneling; quantum hysteresis

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