A Predictive Theory-Guided and Experimentally Controllable Framework for Rational Design of Two-Dimensional Magnetism: Discovery of a Scandium-Based ScCl Magnet.

Despite the successful realization of intrinsic magnetism in a limited subset of two-dimensional (2D) crystals, the accessible material space and magnetic degrees of freedom remain highly constrained. To address this challenge, a Predictive Theory-guided and Experimentally Controllable (PT-EC) framework is introduced for the discovery and synthesis of 2D magnetic materials. This integrated approach enables systematic exploration of unconventional magnetic phases beyond traditional transition-metal systems and stoichiometric constraints, spanning theoretical screening to experimentally guided synthesis. Crucially, the PT-EC framework establishes a direct bridge between theoretical prediction and experimental realizability, enabling the translation of theoretically designed magnetic phases into physically accessible materials. As a proof-of-concept demonstration, a thermodynamically stable 2D ScCl phase with intrinsic magnetic moments is predicted and realized as ScCl nanoplates within reduced graphene oxide (rGO) membranes, establishing scandium as a magnetic element for the first time. Magnetic measurements reveal robust superparamagnetic behavior spanning a wide temperature range from 1.8 to 400 K, reaching the lowest temperature reported to date among superparamagnetic systems. This study highlights the PT-EC framework as a fundamentally important and innovative strategy for expanding the accessible magnetic phase space and enabling the rational design of novel magnetic states and functionalities.