7 research outputs found
Spin excitations of individual Fe atoms on Pt(111): impact of the site-dependent giant substrate polarization
We demonstrate using inelastic scanning tunneling spectroscopy (ISTS) and
simulations based on density functional theory that the amplitude and sign of
the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111)
surface can be manipulated by modifying the adatom binding site. Since the
magnitude of the measured anisotropy is remarkably small, up to an order of
magnitude smaller than previously reported, electron-hole excitations are weak
and thus the spin-excitation exhibits long lived precessional lifetimes
compared to the values found for the same adatom on noble metal surfaces
Exploring the phase diagram of the two-impurity Kondo problem
A system of two exchange-coupled Kondo impurities in a magnetic field gives
rise to a rich phase space hosting a multitude of correlated phenomena.
Magnetic atoms on surfaces probed through scanning tunnelling microscopy
provide an excellent platform to investigate coupled impurities, but typical
high Kondo temperatures prevent field-dependent studies from being performed,
rendering large parts of the phase space inaccessible. We present an integral
study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo
temperature of only 2.6 K. In order to cover the different regions of the phase
space, the pairs are designed to have interaction strengths similar to the
Kondo temperature. By applying a sufficiently strong magnetic field, we are
able to access a new phase in which the two coupled impurities are
simultaneously screened. Comparison of differential conductance spectra taken
on the atoms to simulated curves, calculated using a third order transport
model, allows us to independently determine the degree of Kondo screening in
each phase.Comment: paper: 14 pages, 4 figures; supplementary: 3 pages, 1 figure, 1 tabl
Spin-orbit coupling effects on spin-phonon coupling in Cd2Os2O7
Spin-orbit coupling (SOC) is essential in understanding the properties of 5d
transition metal compounds, whose SOC value is large and almost comparable to
other key parameters. Over the past few years, there have been numerous studies
on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit
entanglement for those materials with a large SOC. However, it is less studied
and remains an unsolved problem in how the SOC affects the lattice dynamics.
We, therefore, measured the phonon spectra of 5d pyrochlore Cd2Os2O7 over the
full Brillouin zone to address the question by using inelastic x-ray scattering
(IXS). Our main finding is a visible mode-dependence in the phonon spectra,
measured across the metal-insulator transition at 227 K. We examined the SOC
strength dependence of the lattice dynamics and its spin-phonon (SP) coupling,
with first-principle calculations. Our experimental data taken at 100 K are in
good agreement with the theoretical results obtained with the optimized U = 2.0
eV with SOC. By scaling the SOC strength and the U value in the DFT
calculations, we demonstrate that SOC is more relevant than U to explaining the
observed mode-dependent phonon energy shifts with temperature. Furthermore, the
temperature dependence of the phonon energy can be effectively described by
scaling SOC. Our work provides clear evidence of SOC producing a non-negligible
and essential effect on the lattice dynamics of Cd2Os2O7 and its SP coupling.Comment: 12 pages, 5 figures, accepted for publication at Rapid Communication
in Physical Review
Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping
Based on high-throughput density functional theory calculations, we
investigated the effects of light interstitial H, B, C, and N atoms on the
magnetic properties of cubic Heusler alloys, with the aim to design new
rare-earth free permanent magnets. It is observed that the interstitial atoms
induce significant tetragonal distortions, leading to 32 candidates with large
( 0.4 MJ/m) uniaxial magneto-crystalline anisotropy energies (MAEs) and
10 cases with large in-plane MAEs. Detailed analysis following the the
perturbation theory and chemical bonding reveals the strong MAE originates from
the local crystalline distortions and thus the changes of the chemical bonding
around the interstitials. This provides a valuable way to tailor the MAEs to
obtain competitive permanent magnets, filling the gap between high performance
Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.Comment: 4 gigure
Capabilities and Limitations of the Spin Hamiltonian Formalism in Single Molecule Magnets
The rational design of molecular magnetic materials is an ongoing effort involving physics, materials science, and chemistry. A common approach to design of complexes and interpretation of magnetic data is the spin Hamiltonian formalism. In this approach, magnetic data is interpreted through constants extracted from the parameterization of data. In design, certain structural motifs are pursued, rationalized by the minimization or maximization of terms in the spin Hamiltonian. In this work, monometallic complexes were prepared to simplify magnetic behavior and allow the examination of specific factors that influence single molecule magnetism like coordination geometry, ligand identity, symmetry, and spin-orbit coupling. A series of hydridotris(3-phenylpyrazolylborato) scorpionate compounds are presented, some of which are inadequately described by the parameterization of magnetic data, and others for which the alteration of terms within the spin Hamiltonian gives the predicted result. These discoveries and ramifications for single molecule magnetism will be discussed. A series of dmf adducts of transition metal para-toluenesulfonates is also presented