  PdCoO2 , belonging to a family of triangular oxides called delafossite, is
one of the most conducting oxides. Its in-plane conductivity is comparable to
those of the best metals, and exhibits hydrodynamic electronic transport with
extremely long mean free path at cryogenic temperatures. Nonetheless, it is
nonmagnetic despite the presence of the cobalt ion. Here, we show that a mild
hydrogenation process reduces PdCoO2 thin films to an atomically-mixed alloy of
PdCo with strong out-of-plane ferromagnetism and sign-tunable anomalous Hall
effect. Considering that many other compounds remain little affected under a
similar hydrogenation condition, this discovery may provide a route to creating
novel spintronic heterostructures combining strong ferromagnetism, involving
oxides and other functional materials.
