engleski

Probing magnetic fields on crystals of the nanomagnet Mn_12-acetate by electron paramagnetic resonance

We report on electron paramagnetic resonance (EPR) probing of magnetic fields and magnetic field gradients near the surface of a single crystal of the nanomagnet [Mn_12O_12(CH_3COO_16)(H_2O)_4]2CH_3COOH4H_2O (Mn_12-Ac). As the EPR probe, we utilized a 0.7mm x 30*=micro x 30*=micro fiberous needle of the organic conductor N-methylphenazinium-tetracyanoquinodimethane (NMP-TCNQ), which yields an exeptionally sharp peak, with a 0.2G (20*=microT) width. In the presence of Mn_12-Ac, the probe's peak exhibits splitting on temperature lowering, which depends on the orientation of the Zeeman field relative to the axes of easy magnetisation of the employed Mn_12-Ac crystal.The shifted peaks yield the magnitude of the magnetic field from Mn_12-Ac crystal to which the various fibers of the probe are subjected. In conjuction with electron mocroscopy, the shifts yield the field gradient at the crystal surface and its change with temperature. For Mn_12-Ac at 10K, the surface magnetic field was measured to be in the mT range and its gradient on the order of 50T/m.

Mn_12-acetate; EPR; NMP-TCNQ

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