Precise resonant experiments on ${\mathrm{Fe}}_8$ magnetic clusters have been conducted down to 1.2 K at various tranverse magnetic fields, using a cylindrical resonator cavity with 40 different frequencies between 37 and 110 GHz. All the observed resonances for both single crystal and oriented powder have been fitted by the eigenstates of the Hamiltonian $\mathcal{H}=-{\mathrm{DS}}_z^2{+ES}_x^2-g{\mu }_B\mathbf{H}\cdot \mathbf{S}{+C(S}_{+}^4{+S}_{-}^4).\mathrm{}$ We have identified the resonances corresponding to the coherent quantum oscillations for different orientations of spin $S=10.\mathrm{}$

• Received 19 April 2000

DOI:https://doi.org/10.1103/PhysRevB.62.3018