Bulk ferromagnetic tips for spin-polarized scanning tunneling microscopy

To develop nano-controlled magnetic materials for condensed matter physics and device applications, it has been required to investigate magnetic structures in atomic scales. While spin-polarized scanning tunneling microscopy (SP-STM) is one of the powerful tools, the usage is still hampered because of the issue on its probe. Tips coated with magnetic thin films are often used, but fabricating stable and reliable ones is not easy unless well equipped. Among the bulk magnetic probes, which can be prepared rather easily, chemically etched antiferromagnetic Cr tips are most commonly used. However, antiferromagnetic probes have disadvantages that the magnetization direction cannot be controlled and defined. On the other hand, bulk ferromagnetic probes are good choices if target materials are robust against stray fields such as antiferromagnetic materials.
In this study, we demonstrate that chemically etched bulk ferromagnetic Ni and Fe tips are ones of the best choices for reliable SP-STM probes using an antiferromagnetic spin-spiral sample; Mn double layers formed on W(110). We also demonstrated that their magnetization direction can be easily controlled by external magnetic fields. This work provides new options for the magnetic probes, opening up versatility of SP-STM.