Magnetization Process of Nanoscale Iron Cluster

Low-temperature magnetization process of the nanoscale iron cluster in linearly sweeped fields is investigated by a numerical analysis of time-dependent Schr$\ddot{\rm o}$dinger equation and the quantum master equation. We introduce an effective basis method extracting important states, by which we can obtain the magnetization process effectively. We investigate the structure of the field derivative of the magnetization. We find out that the antisymmetric interaction determined from the lattice structure reproduces well the experimental results of the iron magnets and that this interaction plays an important role in the iron cluster. Deviations from the adiabatic process are also studied. In the fast sweeping case, our calculations indicate that the nonadiabatic transition dominantly occurs at the level crossing for the lowest field. In slow sweeping case, due to the influence of the thermal environment to the spin system, the field derivative of the magnetization shows an asymmetric behavior, the magnetic F$\ddot{\rm o}$hn effect, which explains the substructure of the experimental results in the pulsed field.Comment: 5 pages of text and 2 pages of 6 figures. To appear in J. Phys. Soc. Jp