Toward a systematic discovery of artificial functional magnetic materials

Phys. Rev. B 104, 014428 (2021)

L. Botsch, P.D. Esquinazi, C. Bundesmann, and D. Spemann

Although ferromagnets are found in all kinds of technological applications, only a few substances are known to be intrinsically ferromagnetic at room temperature. In the past 20 years, a plethora of new artificial ferromagnetic materials have been found by introducing defects into nonmagnetic host materials. In contrast to the intrinsic ferromagnetic materials, they offer an outstanding degree of material engineering freedom, provided one finds a type of defect to functionalize every possible host material to add magnetism to its intrinsic properties. Still, one controversial question remains: Are these materials really technologically relevant ferromagnets? To answer this question, in this work the emergence of a ferromagnetic phase upon ion irradiation is systematically investigated both theoretically and experimentally. Quantitative predictions are validated against experimental data from the literature of SiC hosts irradiated with high-energy Ne ions and own experiments on low-energy Ar ion irradiation of TiO2 hosts. In the high-energy regime, a bulk magnetic phase emerges, which is limited by host lattice amorphization, whereas at low ion energies an ultrathin magnetic layer forms at the surface and evolves into full magnetic percolation. Lowering the ion energy, the magnetic layer thickness reduces down to a bilayer, where a perpendicular magnetic anisotropy appears due to magnetic surface states.