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Low-field EPR Studies of Levels near the Top of the Barrier in Mn12-Acetate Reveal a New Magnetization Relaxation Pathway

We show that X-band electron paramagnetic resonance (EPR) measurements using a dual-mode resonance cavity can directly probe the levels near the top of the magnetization reversal barrier in the single-molecule magnet (SMM) Mn12-acetate. The observed transitions are much sharper than those reported in high-field EPR studies. The observed temperature dependence of the line positions points to the presence of a spin-diffusional mode. The correlation time for such fluctuations is of the order of 6 10-8 s at 10 K, and follows an Arrhenius activation energy of 35-40 K. These results open a new avenue for understanding the mechanism of tunneling and spin-lattice relaxations in these SMMs.

Mn12-Ac; EPR

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