Transient Engineered Multigranular Superstructures in Binary Transition‐Metal Alloys for Enhanced Nanomagnetic Properties

As high-density information storage, integrated magnetic sensors, and ultrathin wearable devices continue to advance, nanoscale multielement transition-metal alloys are required to retain stable exchange coupling, anisotropy, and resistance to thermally activated magnetization fluctuations. Here, we develop a binary CoNi multigranular superstructure (MGS), enabled by pulsed Joule heating, to reconstruct magnetic coupling states and stabilize collective magnetism at the nanoscale. Specifically, transient energy fluctuations drive structural reconfiguration, yielding high-density interfacial networks and locally coherent magnetic units within individual superstructures. Reinforced interfacial pinning and dual magnetic coupling strengthen exchange interactions and suppress magnetothermal perturbations, thereby alleviating nanoscale-induced magnetic degradation. The CoNi nanoalloy with the MGS achieves a ∼400% enhancement in coercivity and a 208% improvement in permeability relative to the conventionally annealed CoNi sample, outperforming representative ferromagnetic alloys. Moreover, the superstructure exhibits over 50% effective absorption across 5G wireless spectrum with thermal stability from 300 to 800 K. This work establishes a practical route to enhance the magnetic properties of binary transition-metal nanoalloys for flexible, high-performance electromagnetic (EM) devices.