Site-Decorated Model for Unconventional Frustrated Magnets: Ultranarrow Phase Crossover and Spin Reversal Transition

Abstract: The site-decorated Ising model is introduced to advance the understanding and experimental realization of the recently discovered one-dimensional finite-temperature ultranarrow phase crossover in an external magnetic field, while mitigating the geometric complexities of traditional bond-decorated models. Furthermore, although higher-dimensional Ising models in an external field remain unsolved, an exact solution for a novel spin-reversal transition -- driven by an exotic, hidden ``half-ice, half-fire'' state induced by site decoration -- is derived. This transition, triggered by a slight variation in temperature or magnetic field even in the weak-field limit, offers a promising route toward energy-efficient applications such as data storage and processing. The results establish site decoration as a compelling new avenue for materials and device design, particularly in systems such as mixed $d$-$f$ compounds, optical lattices, and neural networks.