Magnetization steps in nanomagnets induced by a time-dependent magnetic field: Application to Fe4

The magnetic behavior of the molecular nanomagnet Fe4 is very well simulated by a single spin model Hamiltonian in a crystal field with S=5. The crystal field parameters were determined previously from the inelastic neutron scattering (INS) spectra. Here we show that also the magnetization jumps observed in a time-dependent magnetic field can be explained by a convenient choice of the crystal field parameters consistent with the INS spectra. Indeed the solution of both the time-dependent Schrödinger equation to account for the quantum tunneling of the magnetization and of the master equation to account for the relaxation towards equilibrium of the excited states, occupied by quantum tunneling, leads to a scenario in good agreement with experimental data.