Room‐Temperature Insulating Ferromagnetic (Ni,Co)1+2xTi1−xO3 Thin Films

• Published in: Annalen der Physik 2019-11, Vol.531 (11), p.n/a
• Main Authors: Fujioka, Yukari, Frantti, Johannes, Rouleau, Christopher, Puretzky, Alexander, Gai, Zheng, Lavrik, Nickolay, Herklotz, Andreas, Ivanov, Ilia, Meyer, Harry
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Cobalt; Corundum; corundum compounds; Coupling; Crystals; Ferromagnetic materials; Ilmenite; ilmenites; insulating ferromagnet; Magnetism; Magnons; MATERIALS SCIENCE; nickel cobalt titanates; Room temperature; Thin films
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201900299

Insulating uniaxial room‐temperature ferromagnets are a prerequisite for commonplace spin wave‐based devices, the obstacle in contemporary ferromagnets being the coupling of ferromagnetism with large conductivity. It is shown that the uniaxial A1 + 2xTi4+1 − xO3 (ATO), A = Ni2+,Co2+, and 0.6 < x ≤ 1, thin films are electrically insulating ferromagnets already at room temperature. The octahedra network of the ATO and the corundum and ilmenite structures are the same yet different octahedra‐filling proved to be a route to switch from the antiferromagnetic to ferromagnetic regime. Octahedra can continuously be filled up to x = 1, or vacated (−0.24 < x < 0) in the ATO structure. TiO‐layers, which separate the ferromagnetic (Ni,Co)O‐layers and intermediate the antiferromagnetic coupling between the ferromagnetic layers in the NiTiO3 and CoTiO3 ilmenites, can continuously be replaced by (Ni,Co)O‐layers to convert the ATO‐films to ferromagnetic insulator with abundant direct cation interactions. A uniaxial room‐temperature ferromagnetic (FM) insulator thin film material is formed by continuously replacing TiO‐layers in the antiferromagnetic (AFM) (Ni,Co)TiO3 ilmenite by (Ni,Co)O‐layers. The fraction of replaced TiO‐units is adjustable and all can be replaced. Electric insulation eliminates Eddy currents and provides a route for energy efficient devices. Application examples are sensor and memory, all‐spin‐logic, and radio frequency devices.