Ferromagnetism and sign-tunable anomalous hall effect in PdCoO₂ via hydrogenation

The metallic delafossites, which are among the highest conductivity materials, have recently emerged as an interesting system for materials research. In particular, PdCoO₂ has an extremely long electron mean free path, and its layered crystal structure results in a large anisotropy between the in-plane and out-of-plane direction, making it an outstanding candidate for studying electronic behaviors. However, none of the delafossites are ferromagnetic, mainly as a result of the underlying triangular-lattice. However, we find that it is possible to make PdCoO₂ films strongly ferromagnetic, via hydrogenation. In this process, the crystal transforms into a structure consisting of layers of intermixed Pd and Co, and results in a ferromagnet with strong out-of-plane anisotropy and a high Curie temperature of ~650 K. Furthermore, these films exhibit anomalous hall effect whose sign can be switched by controlling the hydrogenation parameters. This work shows that it is possible to introduce changes to the magnetic and electronic properties of delafossites via hydrogenation.