Structural High-Entropy FePt Alloy Nanoparticles Enabled Fast Magnetization Dynamics.

While interfacial chiral symmetry breaking enables magnetization control in two-dimensional materials, achieving precise modulation in ultrasmall zero-dimensional magnetic nanoparticles remains challenging due to spin scattering lengths comparable to particle dimensions. Here, we establish a crystal symmetry-breaking paradigm using structural high-entropy FePt nanoparticles (merely 4 nm)─featuring chemically disordered face-centered cubic (FCC) phases and quadruple grain boundaries─to manipulate zero-dimensional magnetization dynamics. These nanoparticles exhibit coexisting short-range FCC structural order (separated by the grain boundary network) with atomic-scale chemical disorder. This unique synergy collectively suppresses orbital hybridization and decoheres spin-orbit coupling, drastically reducing magnetic anisotropy (K = 4 × 105 J m-3, merely 4% of FCT-FePt) while enhancing magnetic susceptibility by an order of magnitude. Consequently, equilibrium magnetic relaxation accelerates significantly (τfwhm = 79.4 ns), demonstrating efficient magnetization control tailored to nanoscale applications.