Magnetization spinodal: A mechanism of magnetization switching

Magnetization switching is fundamental to the functional properties and technological applications of ferromagnetic materials. Currently, three mechanisms of magnetization switching have been identified through theoretical and experimental studies: domain wall motion, coherent rotation, and magnetization curling. Here, we report a different mechanism of magnetization switching characterized by uniform and continuous transformation of a single ferromagnetic microdomain into alternating nanodomains of two magnetization vectors with different directions. Such a “magnetization spinodal” mechanism occurs at the ferromagnetic morphotropic phase boundary (MPB) of the Tb_1−xDy_xFe₂ system when the magnetization vector of the microdomain is located within the region on the free energy curve with respect to the magnetization direction where the second derivative becomes negative, which is similar to the compositional spinodal mechanism in diffusional phase transformations. Further calculations show that magnetization spinodal mechanism enables easier magnetization rotation as compared to coherent magnetization rotation and contributes to large magnetostriction at MPB. This finding could advance the theory of magnetization switching and phase transitions. It could also shed light on the design of ferromagnetic devices.