The magnetic ac susceptibility χ of oriented Mn12Ac crystallites has been measured as a function of temperature, field, and frequency. The field has been applied at different values of the angle θ with respect to the sample easy axis. For T= 5 K, the isothermal and adiabatic χ limits have been determined as a function of field. For θ=0° and intermediate frequencies, Lorentzian-shaped peaks have been observed at magnetic field values Hn=nH1 with n=0, 1, and 2 where H1=4.1 kOe. As θ increases these maxima shift to higher fields, that satisfy Hncosθ=const, and decrease in amplitude. The relaxation time τ1 follows Arrhenius' law with respect to temperature and decreases sharply at H=Hn. The observed phenomenology unambiguously proves the existence of field-tuned tunneling between excited magnetic states which are thermally populated. At 5 K, the effective activation energy and the spin states involved in the tunneling process have been obtained.
|Original language||English (US)|
|Number of pages||9|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 1 1997|
ASJC Scopus subject areas
- Condensed Matter Physics