Abstract
We have investigated the magnetic properties of the Ni films deposited on a GaAs and a Bi2Se3 buffer grown by molecular beam epitaxy on a GaAs (001) substrate. The magnetization measurements at 4 K revealed that the coercivity of the Ni films decreases monotonically with increasing thickness up to 25 nm in both cases. However, the coercivity measured at 4 K was always larger in the Ni film deposited on the surface of Bi2Se3 than in the film deposited on the GaAs. Such enhancement of the coercivity decreases with increasing temperature and film thickness. This suggests that the Bi2Se3 surface alters the magnetic properties of the Ni film. The increase of the coercivity was more serious in an un-capped Ni/Bi2Se3 sample, which showed an exchange bias effect due to the oxidation of the top surface of the Ni film. These observations are important for the investigation of spin dependent phenomena in magnetic systems involving a ferromagnet/topological insulator interface.
Highlights
Ferromagnetic materials, such as Fe, Ni, and Co etc., have been broadly used in a wide range of magnetic devices, in which the information is stored via the direction of the magnetization
The magnetic anisotropy of the magnetic atoms deposited on the topological insulator (TI) surface has been investigated by scanning tunneling microscopy (STM),[15,16,17,18] which showed the preference of the spin direction for the magnetic atom depending on the TI surface
The width of the hysteresis (2Hc) decreases with an increasing thickness of Ni film in both series. This thickness dependent behavior is consistent with the previous report, in which the coercive field of the Ni film deposited on GaAs surface continuously decreases with increasing thickness of Ni film up to 32 nm.[23]
Summary
Ferromagnetic materials, such as Fe, Ni, and Co etc., have been broadly used in a wide range of magnetic devices, in which the information is stored via the direction of the magnetization. The use of Bi2Se3 as a buffer layer for the growth of Ni film has special meaning since the Bi2Se3 is a new type of quantum matter called the topological insulator (TI), which shows exotic surface properties originated from the strong spin-orbit coupling effect.[7,8,9,10] It is, expected that the magnetic property of the ferromagnetic film deposited on the TI surface will be significantly different from that grown on normal semiconductors or insulators.[11,12,13,14] The magnetic anisotropy of the magnetic atoms deposited on the TI surface has been investigated by scanning tunneling microscopy (STM),[15,16,17,18] which showed the preference of the spin direction for the magnetic atom depending on the TI surface.
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