Magnetic anisotropy Berry's phase

By considering the intrinsic anisotropy, present in almost all magnetic systems, as a perturbation to the usual Zeeman term, we show that the spin-spin dipolar interaction also known as zero-field splitting (ZFS) leads to an extra geometrical phase in addition to the conventional Berry's phase. Furthermore, we suggest some ways to observe the energy shift in electron paramagnetic resonance spectra due to Berry's phase and how we can separate it from the conventional Zeeman Berry's phase. One of the authors (MM) dedicates this work to the memory of his mother, Djabou Zoulikha, who died on 3 February 2019.