Imaging a chemisorption process: At low temperatures, a molecule may adsorb to a surface only through weak forces (physisorption), and only upon heating and overcoming an energetic barrier does it form a strong covalent bond (chemisorption). Huber et al. imaged this transition for an atomic force microscopy tip terminating in a carbon monoxide molecule. Although the oxygen atom of the tip is normally considered to act like a rare gas atom, interacting only through van der Waals interactions, at short distances directly above a transition metal atom, it transitions to a strongly interacting chemisorption state. Science , this issue p. 235

Zero- and finite-temperature (T) first-principles calculations versus composition (c) show that magnetochemical effects lead to Invar anomalies in Fe-(Ni, Co, Pt) alloys. Chemical short- or long-range order and negative interatomic exchange interaction of electrons in antibonding majority-spin states force the face-centered-cubic lattice to compete simultaneously for a smaller volume (from antiferromagnetic tendencies) and a larger volume (from Stoner ferromagnetic tendencies). The resulting additional negative lattice anharmonicity is very large for Fe-(Ni, Co) while absent for Fe-Pt. Our results explain the T- and c-dependent behavior of Invar properties, including the lattice softening and thermal expansion of Fe-Ni. In addition, the occurrence of a noncollinear spin structure at $T=0\mathrm{}\hspace{0.5em}\mathrm{K}$ near Invar can be understood on the basis of our results.

An extension of the Heisenberg Hamiltonian is discussed that allows us to go beyond the standard bilinear spin Hamiltonian taking into account various contributions due to multispin interactions having both chiral and nonchiral character. The parameters of the extended Hamiltonian are calculated from first principles within the framework of the multiple-scattering Green's function formalism giving access to an explicit representation of these parameters in real space. The discussions are focused on the chiral interactions, i.e., biquadratic and three-spin Dzyaloshinskii-Moriya-like vector interactions ${\vec{\mathcal{D}}}_{ijij}$ (BDMI) and ${\vec{\mathcal{D}}}_{ijkj}$ (TDMI), respectively, as well as the three-spin chiral interaction $J_{ijk}$. Although all parameters are driven by spin-orbit coupling (SOC), some differences in their properties are demonstrated by calculations for real materials. In particular it is shown that the three-spin chiral interactions $J_{ijk}$ may be topology as well as SOC induced, while the TDMI is associated only with the SOC. As the magnitude of the chiral interactions can be quite sizable, they can lead to a stabilization of a noncollinear magnetic texture in some materials that is absent when these interactions are neglected.

Symmetry and magnitude of spin-orbit torques (SOT), i.e., current-induced torques on the magnetization of systems lacking inversion symmetry, are investigated in a fully relativistic linear response framework based on the Kubo formalism. By applying all space-time symmetry operations contained in the magnetic point group of a solid to the relevant response coefficient, the torkance expressed as torque-current correlation function, restrictions to the shape of the direct and inverse response tensors are obtained. These are shown to apply to the corresponding thermal analogs as well, namely the direct and inverse thermal SOT in response to a temperature gradient or heat current. Using an implementation of the Kubo-Bastin formula for the torkance into a first-principles multiple-scattering Green function framework and accounting for disorder effects via the so-called coherent potential approximation, all contributions to the SOT in pure systems, dilute as well as concentrated alloys can be treated on equal footing. This way, material specific values for all torkance tensor elements in the fcc (111) trilayer alloy system $\text{Pt}|{\mathrm{Fe}}_x{\mathrm{Co}}_{1-x}|\mathrm{Cu}$ are obtained over a wide concentration range and discussed in comparison to results for electrical and spin conductivity, as well as to previous work—in particular concerning symmetry with respect to magnetization reversal and the nature of the various contributions.

Systematic trends in the magnetism of Co-Pt solid-state systems are explored by studying the effects of composition, electron correlations, spin-orbit coupling (SOC), and long-range order. Ab initio fully relativistic calculations were performed for bulk Co, a substitutional Pt impurity in Co, ${\text{Co}}_3\text{Pt}$, CoPt, ${\text{CoPt}}_3$, and a substitutional Co impurity in Pt. Many-body effects beyond the local spin-density approximation (LSDA) were included via the dynamical mean-field theory (DMFT); a comparison with results based on the Brooks orbital-polarization (OP) scheme was also made. The disorder was treated within the coherent-potential approximation. We found that while the spin magnetic moments ${\mu }_{\text{spin}}$ at the Co atoms monotonously increase with increasing Pt concentration, the orbital magnetic moments ${\mu }_{\text{orb}}$ do not follow the trend of ${\mu }_{\text{spin}}$. Magnetic moments ${\mu }_{\text{spin}}$ and ${\mu }_{\text{orb}}$ at Pt atoms do not depend on Pt concentration monotonously. Most of these trends can be understood in terms of hybridization and site-dependent SOC. The OP scheme of Brooks corrects the deficiencies of a pure LSDA only if the Pt concentration is low. The $\text{LSDA}+\text{DMFT}$ scheme provides ${\mu }_{\text{orb}}/{\mu }_{\text{spin}}$ ratios for Co atoms which agree with experiment even for high Pt content. Introducing disorder leads to an enhancement of ${\mu }_{\text{spin}}$ at Co atoms and to a suppression of ${\mu }_{\text{spin}}$ at Pt atoms. The ${\mu }_{\text{orb}}$ at Co atoms does not exhibit any systematic dependence on the degree of order, while ${\mu }_{\text{orb}}$ at Pt atoms decreases with increasing disorder for all Pt concentrations.

The finite-temperature transport properties of FeRh compounds are investigated by first-principles density-functional-theory-based calculations. The focus is on the behavior of the longitudinal resistivity with rising temperature, which exhibits an abrupt decrease at the metamagnetic transition point, $T=T_m$, between ferro- and antiferromagnetic phases. A detailed electronic structure investigation for $T\ge 0$ K explains this feature and demonstrates the important role of (i) the difference of the electronic structure at the Fermi level between the two magnetically ordered states and (ii) the different degree of thermally induced magnetic disorder in the vicinity of $T_m$, giving different contributions to the resistivity. To support these conclusions, we also describe the temperature dependence of the spin-orbit-induced anomalous Hall resistivity and Gilbert damping parameter. For the various response quantities considered, the impact of thermal lattice vibrations and spin fluctuations on their temperature dependence is investigated in detail. Comparison with corresponding experimental data shows, in general, very good agreement.