Emergent Magnetism with Continuous Control in the Ultrahigh-Conductivity Layered Oxide PdCoO₂

The current challenge to realizing continuously tunablemagnetismlies in our inability to systematically change properties, such asvalence, spin, and orbital degrees of freedom, as well as crystallographicgeometry. Here, we demonstrate that ferromagnetism can be externallyturned on with the application of low-energy helium implantation andcan be subsequently erased and returned to the pristine state viaannealing. This high level of continuous control is made possibleby targeting magnetic metastability in the ultrahigh-conductivity,nonmagnetic layered oxide PdCoO2 where local lattice distortionsgenerated by helium implantation induce the emergence of a net momenton the surrounding transition metal octahedral sites. These highlylocalized moments communicate through the itinerant metal states,which trigger the onset of percolated long-range ferromagnetism. Theability to continuously tune competing interactions enables tailoringprecise magnetic and magnetotransport responses in an ultrahigh-conductivityfilm and will be critical to applications across spintronics.