12 research outputs found
Antiferromagnetic MnNi tips for spin-polarized scanning probe microscopy
Spin-polarized scanning tunneling microscopy (SP-STM) measures tunnel
magnetoresistance (TMR) with atomic resolution. While various methods for
achieving SP probes have been developed, each is limited with respect to
fabrication, performance, and allowed operating conditions. In this study, we
present the fabrication and use of SP-STM tips made from commercially available
antiferromagnetic foil. The tips are intrinsically SP,
which is attractive for exploring magnetic phenomena in the zero field limit.
The tip material is relatively ductile and straightforward to etch. We
benchmark the conventional STM and spectroscopic performance of our tips and
demonstrate their spin sensitivity by measuring the two-state switching of
holmium single atom magnets on MgO/Ag(100)
On the importance of measuring accurately LDOS maps using scanning tunneling spectroscopy in materials presenting atom-dependent charge order: the case of the correlated Pb/Si(111) single atomic layer
We show how to properly extract the local charge order in two-dimensional
materials from scanning tunneling microscopy/spectroscopy (STM/STS)
measurements. When the charge order presents spatial variations at the atomic
scale inside the unit cell and is energy dependent, particular care should be
taken. In such cases the use of the lock-in technique, while acquiring an STM
topography in closed feedback loop, leads to systematically incorrect dI/dV
measurements giving a false local charge order. A correct method is either to
perform a constant height measurement or to perform a full grid of dI/dV(V)
spectroscopies, using a bias voltage setpoint outside the material bandwidth
where the local density-of-states (LDOS) is spatially homogeneous. We take as a
paradigmatic example of two-dimensional material the 1/3 single-layer
Pb/Si(111). As large areas of this phase cannot be grown, charge ordering in
this system is not accessible to angular resolved photoemission or grazing
x-ray diffraction. Previous investigations by STM/STS supplemented by {\it ab
initio} Density Functional Theory (DFT) calculations concluded that this
material undergoes a phase transition to a low-temperature
reconstruction where one Pb atom moves up, the two remaining Pb atoms shifting
down. A third STM/STS study by Adler {\it et al.} [PRL 123, 086401 (2019)] came
to the opposite conclusion, i.e. that two Pb atoms move up, while one Pb atom
shifts down. This latter erroneous conclusion comes from a misuse of the
lock-in technique. In contrast, using a full grid of dI/dV(V) spectroscopy
measurements, we show that the energy-dependent LDOS maps agree very well with
state-of-the-art DFT calculations confirming the one-up two-down charge
ordering. This structural and charge re-ordering in the unit cell
is equally driven by electron-electron interactions and the coupling to the
substrate.Comment: 11 pages, 3 figure
Engineering atomic-scale magnetic fields by dysprosium single atom magnets
Atomic scale engineering of magnetic fields is a key ingredient for miniaturizing quantum devices and precision control of quantum systems. This requires a unique combination of magnetic stability and spin-manipulation capabilities. Surface-supported single atom magnets offer such possibilities, where long temporal and thermal stability of the magnetic states can be achieved by maximizing the magnet/ic anisotropy energy (MAE) and by minimizing quantum tunnelling of the magnetization. Here, we show that dysprosium (Dy) atoms on magnesium oxide (MgO) have a giant MAE of 250 meV, currently the highest among all surface spins. Using a variety of scanning tunnelling microscopy (STM) techniques including single atom electron spin resonance (ESR), we confirm no spontaneous spin-switching in Dy over days atâââ1 K under low and even vanishing magnetic field. We utilize these robust Dy single atom magnets to engineer magnetic nanostructures, demonstrating unique control of magnetic fields with atomic scale tunability
Antiferromagnetic MnNi tips for spin-polarized scanning probe microscopy
Spin-polarized scanning tunneling microscopy (SP-STM) measures magnetoresistance with atomic resolution. While various methods for achieving SP probes have been developed, each is limited with respect to fabrication, performance, and operating conditions. In this study, we present the fabrication and use of SP-STM tips made from commercially available antiferromagnetic Mn88Ni12 foils. The tips are intrinsically SP, which is attractive for exploring magnetic phenomena in the zero field limit. The tip material is relatively ductile, is straightforward to etch, and has a NĂ©el temperature exceeding 300 K. We benchmark the topographic and spectroscopic performance of our tips and demonstrate their spin sensitivity by measuring the two-state switching of holmium single atom magnets on MgO/Ag(100)
Importance of accurately measuring LDOS maps using scanning tunneling spectroscopy in materials presenting atom-dependent charge order: The case of the correlated Pb/Si(111) single atomic layer
International audienc
Chiral Spin Texture in the Charge-Density-Wave Phase of the Correlated Metallic Pb/Si(111) Monolayer
We investigate the 1/3 monolayer alpha-Pb/Si(111)) surface by scanning
tunneling spectroscopy (STS) and fully relativistic first-principles
calculations. We study both the high-temperature root 3 x root/3 and
low-temperature 3 x3 reconstructions and show that, in both phases, the
spin-orbit interaction leads to an energy splitting as large as 25% of
the valence-band bandwidth. Relativistic effects, electronic
correlations, and Pb-substrate interaction cooperate to stabilize a
correlated low-temperature paramagnetic phase with well-developed lower
and upper Hubbard bands coexisting with 3 x 3 periodicity. By comparing
the Fourier transform of STS conductance maps at the Fermi level with
calculated quasiparticle interference from nonmagnetic impurities, we
demonstrate the occurrence of two large hexagonal Fermi sheets with
in-plane spin polarizations and opposite helicities