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Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin–orbit‐related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low‐energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin–orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature‐dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin–orbit coupling at the interface is key to exploring spintronic devices with new functionalities. [ABSTRACT FROM AUTHOR]

High-temperature ferromagnetism in materials composed of non-magnetic constituents is one of the most intriguing aspects in condensed matter physics as well as materials science. Beyond oxide compounds where the ferromagnetism is mainly induced by dilute magnetic dopants, a variety of unusual ferromagnetic materials, mostly fabricated artificially to control the magnetic and electronic properties, have been investigated for spintronic device applications. The unexpected ferromagnetism, attributed to strain and structural defects or proximity and interfacial effects, is now extended to quantum materials, despite prevailing controversy on its physical origin. Recently, the ferromagnetism observed in topological materials with high mobility arising from the linear energy dispersion invokes new interest in the field of spintronics. Here, we report experimental verification of peculiar high-temperature ferromagnetism in β -Ag 2 Se topological semimetal, composed of non-magnetic constituents. We have fabricated stoichiometric Ag 2 Se (S-Ag 2 Se) and Ag-vacant Ag 2 Se (V-Ag 2 Se) samples. Contrary to non-magnetic behavior of S-Ag 2 Se, V-Ag 2 Se shows distinct ferromagnetic response up to room temperatures. First-principles calculations demonstrate that the ferromagnetic ordering occurs only in V-Ag 2 Se if there is finite Hubbard U , which can be explained by self-trapped magnetic polaron model with strong p - d hybridization. High-temperature ferromagnetism, especially in topological materials, allows exploring a significant new direction in material engineering for spintronic applications. [Display omitted] • Ferromagnetism in a topological semimetal β -Ag 2 Se composed of non-magnetic constituents. • Tunable magnetization by the excessive amount of Se. • Invariant non-trivial π Berry's phase in non-magnetic and magnetic β -Ag 2 Se. [ABSTRACT FROM AUTHOR]