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Atomic spin structures assembled by means of scanning tunneling microscopy (STM) provide valuable insight into the understanding of atomic-scale magnetism. Among the major challenges are the detection and subsequent read-out of ultrafast spin dynamics due to a dichotomy in travel speed of these dynamics and the probe tip. Here, we present a device composed of individual Fe atoms that allows for remote detection of spin dynamics. We have characterized the device and used it to detect the presence of spin waves originating from an excitation induced by the STM tip several nanometres away; this may be extended to much longer distances. The device contains a memory element that can be consulted seconds after detection, similar in functionality to e.g. a single photon detector. We performed statistical analysis of the responsiveness to remote spin excitations and corroborated the results using basic calculations of the free evolution of coupled quantum spins. Scanning probe microscopy offers a creative way of fabricating structures by combining unmatched atomic-scale resolution and advanced functionalities. The authors utilize this technique to implement a novel spin chain configuration that, by means of a memory unit, can probe ultra-fast spin dynamics. [ABSTRACT FROM AUTHOR]

We describe the design, development and performance of a scanning probe microscopy (SPM) facility operating at a base temperature of 10 mK in magnetic fields up to 15 T. The microscope is cooled by a custom designed, fully ultra-high vacuum (UHV) compatible dilution refrigerator (DR) and is capable of in situ tip and sample exchange. Subpicometer stability at the tip-sample junction is achieved through three independent vibration isolation stages and careful design of the dilution refrigerator. The system can be connected to, or disconnected from, a network of interconnected auxiliary UHV chambers, which include growth chambers for metal and semiconductor samples, a field-ion microscope for tip characterization, and a fully independent additional quick access low temperature scanning tunneling microscope (STM) and atomic force microscope (AFM) system. To characterize the system, we present the cooling performance of the DR, vibrational, tunneling current, and tip-sample displacement noise measurements. In addition, we show the spectral resolution capabilities with tunneling spectroscopy results obtained on an epitaxial graphene sample resolving the quantum Landau levels in a magnetic field, including the sublevels corresponding to the lifting of the electron spin and valley degeneracies. [ABSTRACT FROM AUTHOR]

Magnetic anisotropy allows magnets to maintain their direction of magnetization over time. Using a scanning tunneling microscope to observe spin excitations, we determined the orientation and strength of the anisotropies of individual iron and manganese atoms on a thin layer of copper nitride. The relative intensities of the inelastic tunneling processes are consistent with dipolar interactions, as seen for inelastic neutron scattering. First-principles calculations indicate that the magnetic atoms become incorporated into a polar covalent surface molecular network in the copper nitride. These structures, which provide atom-by-atom accessibility via local probes, have the potential for engineering anisotropies large enough to produce stable magnetization at low temperatures for a single atomic spin. [ABSTRACT FROM AUTHOR]

Full insight into the dynamics of a coupled quantum system depends on the ability to follow the effect of a local excitation in real-time. Here, we trace the free coherent evolution of a pair of coupled atomic spins by means of scanning tunneling microscopy. Rather than using microwave pulses, we use a direct-current pump-probe scheme to detect the local magnetization after a current-induced excitation performed on one of the spins. By making use of magnetic interaction with the probe tip, we are able to tune the relative precession of the spins. We show that only if their Larmor frequencies match, the two spins can entangle, causing angular momentum to be swapped back and forth. These results provide insight into the locality of electron spin scattering and set the stage for controlled migration of a quantum state through an extended spin lattice. [ABSTRACT FROM AUTHOR]

Individual Fe atoms on a Cu2N/Cu(100) surface exhibit strong magnetic anisotropy due to the crystal field. We show that we can controllably enhance or reduce this anisotropy by adjusting the relative position of a second nearby Fe atom, with atomic precision, in a low-temperature scanning tunneling microscope. Local inelastic electron tunneling spectroscopy, combined with a qualitative first-principles model, reveal that the change in uniaxial anisotropy is driven by local strain due to the presence of the second Fe atom. [ABSTRACT FROM AUTHOR]