Inelastic scanning tunneling spectroscopy: magnetic excitations on the nanoscale

Inelastic scanning tunneling spectroscopy is used to study elementary excitations (magnons) in magnetic systems of various dimensions: from bulk to single magnetic atoms. The creation mechanism, the excitation probability, the spectrum and the lifetimes of magnons are investigated

Large Tunneling Anisotropic Magnetoresistance mediated by Surface States

We investigated the tunneling anisotropic magnetoresistance (TAMR) in thick hcp Co films at cryogenic temperatures using scanning tunneling microscopy. At around -350 mV, a strong TAMR up to 30\% is found with a characteristic voltage dependence and a reversal of sign. With the help of \textit{ab initio} calculations the TAMR can be traced back to a spin-polarized occupied surface states that experience a strong spin-orbit interaction leading to a magnetization direction depending hybridization with bulk states

Towards laterally resolved ferromagnetic resonance with spin-polarized scanning tunneling microscopy

We used a homodyne detection to investigate the gyration of magnetic vortex cores in Fe islands on W(110) with spin-polarized scanning tunneling microscopy at liquid helium temperatures. The technique aims at local detection of the spin precession as a function of frequency using a radio-frequency (rf) modulation of the tunneling bias voltage. The gyration was excited by the resulting spin-polarized rf current in the tunneling junction. A theoretical analysis of different contributions to the frequency-dependent signals expected in this technique is given. These include, besides the ferromagnetic resonance signal, also signals caused by the non-linearity of the I(U) characteristics. The vortex gyration was modeled with micromagnetic finite element methods using realistic parameters for the tunneling current, its spin polarization, and the island shape, and simulations were compared with the experimental results. The observed signals are presented and critically analyzed

Friedel Oscillations and superconducting-gap enhancement by impurity scattering

Experiments observe an enhanced superconducting gap over impurities as compared to the clean-bulk value. In order to shed more light on this phenomenon, we perform simulations within the framework of Bogoliubov-deGennes theory applied to the attractive Hubbard model. The simulations qualitatively reproduce the experimentally observed enhancement effect; it can be traced back to an increased particle density in the metal close to the impurity site. In addition, the simulations display significant differences between a thin (2D) and a very thick (3D) film. In 2D pronounced Friedel oscillations can be observed, which decay much faster in (3D) and therefore are more difficult to resolve. Also this feature is in qualitative agreement with the experiment

Indirect Spin-Readout of Rare-Earth-Based Single-Molecule Magnet with Scanning Tunneling Microscopy

Rare-earth based single-molecule magnets are promising candidates for magnetic information storage including qubits as their large magnetic moments are carried by localized 4f electrons. This shielding from the environment in turn hampers a direct electronic access to the magnetic moment. Here, we present the indirect readout of the Dy moment in Bis(phthalocyaninato)dysprosium (DyPc2) molecules on Au(111) using milli-Kelvin scanning tunneling microscopy. Because of an unpaired electron on the exposed Pc ligand, the molecules show a Kondo resonance that is, however, split by the ferromagnetic exchange interaction between the unpaired electron and the Dy angular momentum. Using spin-polarized scanning tunneling spectroscopy, we read out the Dy magnetic moment as a function of the applied magnetic field, exploiting the spin polarization of the exchange-split Kondo state

Stabilizing spin spirals and isolated skyrmions at low magnetic field exploiting vanishing magnetic anisotropy

Skyrmions are topologically protected non-collinear magnetic structures. Their stability is ideally suited to carry information in, e.g., racetrack memories. The success of such a memory critically depends on the ability to stabilize and manipulate skyrmions at low magnetic fields. The non-collinear Dzyaloshinskii-Moriya interaction originating from spin-orbit coupling drives skyrmion formation. It competes with Heisenberg exchange and magnetic anisotropy favoring collinear states. Isolated skyrmions in ultra-thin films so far required magnetic fields as high as several Tesla. Here, we show that isolated skyrmions in a monolayer of Co/Ru(0001) can be stabilized down to vanishing fields. Even with the weak spin-orbit coupling of the 4d element Ru, homochiral spin spirals and isolated skyrmions were detected with spin-sensitive scanning tunneling microscopy. Density functional theory calculations explain the stability of the chiral magnetic features by the absence of magnetic anisotropy energy