We study the magnetic properties of the adatom systems on a semiconductor surface Si(111):{C,Si,Sn,Pb} -(On the basis of all-electron density functional theory calculations we construct effective low-energy models taking into account spin-orbit coupling and electronic correlations. In the ground state the surface nanostructures are found to be insulators with the non-collinear 120• Néel (for C, Si, Sn monolayer coverages) and 120• row-wise (for Pb adatom) antiferromagnetic orderings. The corresponding spin Hamiltonians with anisotropic exchange interactions are derived by means of the superexchange theory and the calculated Dzyaloshinskii-Moriya interactions are revealed to be very strong and compatible with the isotropic exchange couplings in the systems with Sn and Pb adatoms. To simulate the excited magnetic states we solve the constructed spin models by means of the Monte Carlo method. At low temperatures and zero magnetic field we observe complex spin spiral patterns in Sn/Si(111) and Pb/Si(111). On this basis the formation of antiferromagnetic skyrmion lattice states in adatom sp electron systems in strong magnetic fields is discussed.

A quantitative description of the excited electronic states of point defects and impurities is crucial for understanding materials properties, and possible applications of defects in quantum technologies. This is a considerable challenge for computational methods, since Kohn-Sham density-functional theory (DFT) is inherently a ground state theory, while higher-level methods are often too computationally expensive for defect systems. Recently, embedding approaches have been applied that treat defect states with many-body methods, while using DFT to describe the bulk host material. We implement such an embedding method, based on Wannierization of defect orbitals and the constrained random-phase approximation approach, and perform systematic characterization of the method for three distinct systems with current technological relevance: a carbon dimer replacing a B and N pair in bulk hexagonal BN (CBCN), the negatively charged nitrogen-vacancy center in diamond (NV − ), and an Fe impurity on the Al site in wurtzite AlN (Fe Al ). For CBCN we show that the embedding approach gives many-body states in agreement with analytical results on the Hubbard dimer model, which allows us to elucidate the effects of the DFT functional and doublecounting correction. For the NV − center, our method demonstrates good quantitative agreement with experiments for the zero-phonon line of the triplet-triplet transition. Finally, we illustrate challenges associated with this method for determining the energies and orderings of the complex spin multiplets in Fe Al .

The pathway toward the tailored synthesis of materials starts with precise characterization of the conformational properties and dynamics of individual molecules. Electron spin resonance based scanning tunneling microscopy can potentially address molecular structure with unprecedented resolution. Here, we determine the fine structure and geometry of an individual TiH molecule, utilizing a combination of a newly developed mK ESR-STM in a vector magnetic field and ab initio approaches. We demonstrate a strikingly large anisotropy of the g-tensor unusual for a spin doublet ground state, resulting from a non-trivial orbital angular momentum. We quantify the relationship between the resultant fine structure, hindered rotational modes, and orbital excitations. Our model system provides new avenues to determine the structure and dynamics of individual molecules with unprecedented precision. Main textPrecisely determining the fine structure, dynamics, and geometry of an individual molecule, with sub-molecular resolution, is a grand challenge in numerous fields of nanoscience.Scanning probe microscopy (SPM) has emerged as a surface imaging approach capable of intramolecular resolution of individual molecules [1, 2], quantifying conformational modifications like the static Jahn-Teller distortion [3], or light-assisted conformational changes [4]. Complementary to imaging, SPM-based inelastic excitation spectroscopy (ISTS) has been successfully applied to infer the various intramolecular vibrational [5], rotational [6, 7] or hindered rotational modes [8]. However, these methods lack the precision to quantify the interplay between structure and molecular geometry like methods such as electron spin resonance (ESR) [9, 10]. These methods are also not well suited for studying low-energy dynamics, such as the quantum zero-point motion of hydrogen and other light elements that are quenched by strong tip-sample interactions. Moreover, the resolution of traditional SPM, particularly scanning tunneling microscopy (STM), is limited by both convolution [1, 11, 12] and current preamplifier related bandwidth issues that preclude insight into the structure and rotational dynamics of individual molecules. Hybrid methods have recently emerged, combining the spatial resolution of STM with temporal resolution [13, 14] driven by continuous wave excitation [15]. THz-based STM [16, 17] has been used to excite and quantify the vibrational motion of an individual phthalocyanine molecule with picosecond precision [18]. Likewise, electron paramagnetic/spin resonance has been established [15, 19, 20], based on a combination of microwave excitation of the STM junction, with the detection of spin-polarized current [21] of individual atoms. This technique, referred to as ESR-STM, has been used to quantify magnetic interactions, hyperfine couplings, and the coherent dynamics of individual magnetic impurities with unprecedented resolution [22-24]. However, in the spirit of traditional EPR/ESR, ESR-STM has yet to be applied to infer the molecular str...

Magnetic behavior of yavapaiite-type BaMoP2O8 with the spatially anisotropic triangular arrangement of the S = 1 Mo 4+ ions is explored using thermodynamic measurements, neutron diffraction, and density-functional band-structure calculations. A broad maximum in the magnetic susceptibility around 46 K is followed by the stripe antiferromagnetic order with the propagation vector k = ( 1 2 , 1 2 , 1 2 ) formed below TN 21 K. This stripe phase is triggered by a pronounced onedimensionality of the spin lattice, where one of the in-plane couplings, J2 4.6 meV, is much stronger than its J1 0.4 meV counterpart, and stabilized by the weak easy-axis anisotropy. The ordered moment of 1.42(9) µB at 1.5 K is significantly lower than the spin-only moment of 2 µB due to a combined effect of quantum fluctuations and spin-orbit coupling.