Spin-polarized scanning tunnelling microscopy

Abstract

The recent experimental progress in spin-polarized scanning tunnelling microscopy (SP-STM)-a magnetically sensitive imaging technique with ultra-high resolution-is reviewed. The basics of spin-polarized electron tunnelling are introduced as they have been investigated in planar tunnel junctions for different electrode materials, i.e. superconductors, optically excited GaAs, and ferromagnets. It is shown that ferromagnets and antiferromagnets are suitable tip materials for the realization of SP-STM. Possible tip designs and modes of operations are discussed for both classes of materials. The results of recent spatially resolved measurements as performed with different magnetic probe tips and using different modes of operation are reviewed and discussed in terms of applicability to surfaces, thin films, and nanoparticles. The limits of spatial resolution, and the impact of an external magnetic field on the imaging process are debated.

Effect of interface bonding on spin-dependent tunneling from the oxidized Co surface

“…11 Since the ferromagnetic tip is sensitive to the SP of the total local DOS above the surface ͑see, e.g., Ref. 29͒, the tunneling magnetoresistance in the system surface/vacuum/tip should change sign when the Co surface is oxidized.…”

Evolution of Density of States and a Spin-Resolved Checkerboard-Type Pattern Associated with the Majorana Bound State

“…It is worth noticing that, if the energy resolution of STM/STS measurement is high enough, checkerboard patterns can be detected even in individual spin-resolved LDOS (without taking the ratio between signals in two spin channels, see Appendix). Experimentally, spin-resolved LDOS can be obtained by using a spin-polarized STM tip [40]. It is noticed that, with very high resolution splitting in spectral weight due to spin states can be observed even in the total LDOS [41].…”

Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

“…Spin-polarized scanning tunneling microscopy (SP-STM) is a powerful tool for mapping the spin distribution on the surface of a magnetic material down to the atomic scale, [1][2][3][4][5][6][7] and has higher resolution than other magnetic domain observation methods such as magnetic force microscopy (MFM) 8,9 and spin-polarized scanning electron microscopy (spin SEM or SEMPA). 10,11 SP-STM is usually conducted in the constant current mode or the spectroscopic mode where a magnetic tip is used as a spin-polarized current source.…”

“…10,11 SP-STM is usually conducted in the constant current mode or the spectroscopic mode where a magnetic tip is used as a spin-polarized current source. The constant current mode 2,4,6,7 is very simple, but the obtained STM image contains both spin and topographical information. Therefore, SP-STM in this mode is usually applied to an atomically flat single crystal.…”

“…Therefore, SP-STM in this mode is usually applied to an atomically flat single crystal. In the spectroscopic mode, 1,3,[5][6][7] the local differential conductance dI/dU (I: tunneling current, U: bias voltage), which is proportional to the local density of state (LDOS) on the sample, is used as an image signal for spin imaging. The local differential conductance depends not only on the spin direction of the sample but also on the other properties such as the surface crystallographic plane.…”