Magnetic exchange force microscopy (MExFM) is a new technique that was proposed already in [1] to perform magnetic imaging with atomic resolution. It is based on conventional atomic force microscopy using a magnetic tip, which is approached very close to a magnetic sample in order to detect the magnetic exchange interaction force. Unlike spin-polarized scanning tunneling microscopy (SP-STM) [2], it is not limited to conducting materials. Recently, the first successful demonstration of MExFM with atomic scale resolution has been reported on NiO(001) [3].
We have systematically studied the exchange force (EF) of different ferromagnetic tips (Mn, Fe and Co) on a 1ML thin film of Fe on W(001), which is antiferromagnetically ordered [4], by means of first-principles (density functional theory) calculations. From the calculations we obtain the probe-sample separation dependence of the force, energy, magnetic moments, and local density of states (LDOS) for FM and AFM configurations. The results indicate that the EF interaction (difference between FM and AFM interactions) is large enough to be observed using atomic force microscopy allowing atomic scale magnetic resolution. Differences in the EF interaction arise depending on the chemical nature of the tip apex. We discuss the origin of such differences based on the electronic structure of the probe-sample system and illustrate the electronic and magnetic interactions by means of orbital-decomposed LDOS and spin-density plots.
[1] R. Wiesendanger et al., J. Vac. Sci. Technol. B 9, 519 (1990).
[2] M. Bode, Rep. Prog. Phys. 66, 523 (2003).
[3] U. Kaiser, A. Schwarz, and R. Wiesendanger, to appear in Nature.
[4] A. Kubetzka et al., Phys. Rev. Lett. 94, 087204 (2005).
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