For several decades, morphotropic phase boundary (MPB) in ferroelectric materials has attracted constant interest due to
its great enhancement of piezoelectric properties. However, such a MPB has been studied merely in ferroelectric system,
not in ferromagnetic system. Recently, we reported the magnetic MPB in a ferromagnetic system of TbCo2-DyCo2 and
correspondingly a larger magnetostriction (i.e. a piezoelectricity-like phenomenon in ferromagnets) occurs near MPB.
Very surprisingly, such a MPB in TbCo2-DyCo2 system has been ever regarded as a spin reorientation transition (SRT)
where the spontaneous magnetization (Ms) gradually rotates from <111> in TbCo2-rich phase to <001> of DyCo2-rich
phase and vice versa. But, our experiment of synchrotron x-ray diffractometry demonstrates the MPB region is the
coexistence of TbCo2 and DyCo2 phases and hence the Ms cannot rotate gradually from <111> to <001>1. Thus, the
process of magnetization rotation near MPB in a ferromagnetic system of TbCo2-DyCo2 remains obscure due to a lack of
in-situ observation of magnetic moment rotation. In the present work, by using a method of Monte Carlo simulation, we
successfully reproduce the observed effects and furthermore clarify the magnetization rotation process near the magnetic
MPB of TbCo2-DyCo2 systems. Namely, the direction of magnetization changes discontinuously from <111> to <001>
near the MPB via the phase transition process from TbCo2-rich phase to DyCo2-rich phase. Our simulation provides an
effective way to understand the origin of the magnetic MPB.