Field-tuned quantum tunnelling of the magnetization in small magnetic particles

We present staircase magnetization curves for single-spin models of uniaxial magnets as obtained from the numerically exact solution of the time-dependent Schrödinger equation. Steps are shown to correspond to field-tuned tunnelling between different pairs of nearly degenerate energy levels. The role played by second-order and fourth-order transverse anisotropy, the transverse field and the orientation and sweep speed of the applied field are studied. Magnetization curves for excited and non-saturated initial states are also presented. These results are discussed in relation to recent experiments on high-spin compounds