Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

A new scanning tunneling microscope for spin-polarized experiments has been developed. The microscope is operated at 4.7 K in a superconducting triple axis vector magnet providing the possibility for measurements depending on the direction of the magnetic field. In single axis mode the maximum field is 5 T perpendicular to the sample plane and 1.3 T in the sample plane, respectively. In cooperative mode fields are limited to 3.5 T perpendicular and 1 T in plane. The microscope is operated in an ultrahigh vacuum system providing optimized conditions for the self-assembled growth of magnetic structures at the atomic scale. The available temperature during growth ranges from 10 up to 1100 K. The performance of the new instrument is illustrated by spin-polarized measurements on 1.6 atomic layers Fe/W(110). It is demonstrated that the magnetization direction of ferromagnetic Fe and Gd tips can be adjusted using the external magnetic field. Atomic resolution is demonstrated by imaging an Fe monolayer on Ru(0001).

The observation of a novel type of commensurability resonance in two-dimensional, hexagonal antidot lattices is reported. These resonances have a classical character and occur at magnetic fields above the resonance that corresponds to the cyclotron motion around a single antidot. The resonances are visible only for antidots with effective diameters larger than 50 % of the lattice constant. Simulations reveal that they originate from quasi-stable electron trajectories that bounce between three neighboring antidots. This interpretation is backed by the observation of large-period Aharonov-Bohm type oscillations at low temperatures.

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