Melting curves of Cu, Ni, Pd, and Pt were measured in a laser-heated diamond-anvil cell up to 43, 52, 28, and 28 GPa, respectively. The obtained results are compared with previous studies. In particular, the measurements made in Cu are in agreement with the literature. In Pt the experiments are consistent with $Z$ method calculations indicating that earlier measurements probably underestimate the melting temperature of Pt at high pressure. Cu, Pd, and Pt show a qualitative similar melting behavior. In the case of Ni, experiments confirm that it has a low melting slope of 28 K/GPa. Ni is the only transition metal of groups 10 and 11 of the Periodic Table that shows such a slope since the other metals have a steeper melting slope of 41–47 K/GPa. The determined melting curves can be described with Simon equations which are reported. The present results increase the database on high-pressure melting and could contribute to improving the understanding of this phenomenon.

First-principles theoretical investigations of one-dimensional ordered $3d$-$5d$ alloys reveal magnetic anisotropy energies $\Delta E$, which are extraordinary high for transition-metal nanostructures. The results show that $\Delta E$ of Pt-$X$ and Ir-$X$ wires with $X\equiv \text{Ti}$–Ni strongly oscillates as a function $3d$-band filling showing both giant values (e.g., $\Delta E=25$, 58, and 57 meV/atom for Pt-Ni, Ir-Cr, and Ir-Ni) as well as modest enhancements (e.g., $\Delta E=2.3$ and $6.5$ meV/atom for Pt-Cr and Pt-Fe). The robustness of the results with respect to strain and relaxation is demonstrated. The microscopic mechanisms behind the trends in $\Delta E$ are analyzed from a local perspective.

We investigate the switching criteria of magnetic vortices in micron-sized Permalloy squares. The vortices are excited by high frequency magnetic fields. Continuous core reversal is demonstrated for a wide range of frequencies and amplitudes of excitation by ferromagnetic absorption spectroscopy and for selected frequencies and amplitudes with time-resolved scanning x-ray microscopy. The boundary of this switching regime is derived from the Thiele equation when a critical velocity of $v_{\mathrm{crit}}\approx 250{\mathrm{ms}}^{-1}$ is considered.

We present a detailed analysis of the phase diagram of antiferromagnets with competing exchange-driven and field-induced order parameters. By using the quasi-1D antiferromagnet BaCu${}_2$Si${}_2$O${}_7$ as a test case, we demonstrate that a model based on a Landau type of approach provides an adequate description of both the magnetization process and of the phase diagram. The developed model not only accounts correctly for the observed spin-reorientation transitions, but it predicts also their unusual angular dependence.

Dynamical properties of the lattice structure were studied by optical spectroscopy in $A$Cr${}_2$O${}_4$ chromium spinel oxide magnetic semiconductors over a broad temperature region of $T=10$–335 K. The systematic change of the $A$-site ions ($A=$ Mn, Fe, Co, Ni and Cu) showed that the occupancy of 3$d$ orbitals on the $A$ site has strong impact on the lattice dynamics. For compounds with orbital degeneracy (FeCr${}_2$O${}_4$, NiCr${}_2$O${}_4$, and CuCr${}_2$O${}_4$), clear splitting of infrared-active phonon modes and/or activation of silent vibrational modes have been observed upon the Jahn-Teller transition and at the onset of the subsequent long-range magnetic order. Although MnCr${}_2$O${}_4$ and CoCr${}_2$O${}_4$ show multiferroic and magnetoelectric character, no considerable magnetoelasticity was found in spinel compounds without orbital degeneracy as they closely preserve the high-temperature cubic spinel structure even in their magnetic ground state. Aside from lattice vibrations, intra-atomic 3$d$-3$d$ transitions of the $A$${}^{2+}$ ions were also investigated to determine the crystal field and Racah parameters and the strength of the spin-orbit coupling.

Magnetic properties of the spin-$\frac{3}{2}$ Heisenberg system Cr${}_2[$BP${}_3$O${}_{12}]$ are investigated by magnetic susceptibility $\chi \left(T\right)$ measurements, electron spin resonance, neutron diffraction, and density functional theory (DFT) calculations, as well as classical and quantum Monte Carlo (MC) simulations. The broad maximum of $\chi \left(T\right)$ at 85 K and the antiferromagnetic Weiss temperature of 139 K indicate low-dimensional magnetic behavior. Below $T_{\mathrm{N}}=28$ K, Cr${}_2[$BP${}_3$O${}_{12}]$ is antiferromagnetically ordered with the $\mathbf{k}=0$ propagation vector and an ordered moment of 2.5${\mu }_{\mathrm{B}}$/Cr. DFT calculations, including $\text{DFT}+U$ and hybrid functionals, yield a microscopic model of spin chains with alternating nearest-neighbor couplings $J_1$ and $J_1^{\prime }$. The chains are coupled by two nonequivalent interchain exchanges of similar strength ($\sim$1–2 K), but different sign (antiferromagnetic and ferromagnetic). The resulting spin lattice is quasi-one-dimensional and not frustrated. Quantum MC simulations show excellent agreement with the experimental data for the parameters $J_1\simeq 50$ K and $J_1^{\prime }/J_1\simeq 0.5$. Therefore, Cr${}_2[$BP${}_3$O${}_{12}]$ is close to the gapless critical point ($J_1^{\prime }/J_1=0.41$) of the spin-$\frac{3}{2}$ bond-alternating Heisenberg chain. The applicability limits of the classical approximation are addressed by quantum and classical MC simulations. Implications for a wide range of low-dimensional $S=3/2$ materials are discussed.

We have investigated the structural, magnetic, and ferroelectric properties of Mn-substituted CuFeO${}_2$, i.e., CuFe${}_{1-x}$Mn${}_x$O${}_2$ ($0\le x\le 0.2$). CuFeO${}_2$ is a typical frustrated triangular lattice antiferromagnet due to its Fe${}^{3+}$ triangular configuration. Although the lattice constants and atomic bond distances do not change in the range of $0\le x\le 0.2$, structural modulation introduced by the Mn substitution affects the magnetic and dielectric properties. A multiferroic phase, where the antiferromagnetism and ferroelectricity coexist, is found in a narrow range of $0.01\le x\le 0.1$. The origin of the multiferroic characteristics is discussed in terms of the partial release of the spin frustration.

We study the finite-size and boundary effects on a $p$-wave superconductor in a mesoscopic rectangular sample using Ginzburg-Landau and quasiclassical Green's function theory. Apart from a few very special cases, we find that the ground state near the critical temperature always prefers a time-reversal symmetric state, where the order parameter can be represented by a real vector. For large aspect ratio, this vector is parallel to the long side of the rectangle. Within a critical aspect ratio, it has instead a vortexlike structure, vanishing at the sample center.

$\mathit{In}$ $\mathit{situ}$ photoemission spectroscopy and x-ray absorption spectroscopy (XAS) have been performed on LaNiO${}_3$ (LNO) ultrathin films grown on LaAlO${}_3$ substrates to investigate the origin of the thickness-dependent metal-insulator transition (MIT). With decreasing film thickness, the progressive weakening of a quasiparticle peak at the Fermi level ($E_F$) occurs below 10 monolayer (ML), and the further depletion of spectral weight at $E_F$ leads to pseudogap behavior at 3–6 ML. The pseudogap finally evolves into a full gap, indicating that the thickness-dependent MIT takes place at a critical film thickness of 2–3 ML. The observed spectral behavior is in line with the transport properties of LNO ultrathin films. The thickness dependence of the spectral intensity is compared with realistic multiorbital dynamical mean-field theory. The experimental spectral function was found to depend on the film thickness more strongly than the theoretical one for thinner systems, indicating that the thickness-dependent MIT in LNO is caused by the crossover from three to two dimensions, during which the spatial correlations are progressively enhanced. The XAS results suggest that a charge disproportionate state is strongly suppressed in LNO ultrathin films plausibly as a result of epitaxial strain from the substrates. These results strongly suggest that a novel insulating state is realized in LNO films at a thin limit.

The formation of large-area homogeneous graphene on a C-terminated SiC (000$\overline{1}$) surface was achieved via decomposition of the SiC (000$\overline{1}$) surface covered with an ultrathin but much more stable TiC layer than the reactive SiC(000$\overline{1}$). By heating the SiC (000$\overline{1}$) surface with a mixed powder of TiO${}_2$ and carbon at 1500–1550 °C in vacuum, an extremely homogeneous, epitaxial 0.75-nm-thick TiC(111) layer was grown on the SiC(000$\overline{1}$) surface over a millimeter-scale area. Graphitization of the TiC-masked SiC surface led to the growth of high-quality graphene layers, which consist of TiC- and SiC-derived carbon. High-resolution transmission electron microscopy revealed the presence of disordered stacking of graphene layers on SiC through an amorphous layer at the interface. This unique method will promise further progress of relatively high carrier mobility of graphene formed on the SiC (000$\overline{1}$) surface.

We report the electronic and magnetic phase diagram of Ca${}_3$(Ru${}_{1-x}$Ti${}_x$)${}_2$O${}_7$. With Ti doping, the system evolves from a quasi-two-dimensional metal with ferromagnetic (FM) bilayers coupled antiferromagnetically along the $c$ axis (AFM-b) for $x=0$, to a weakly localized state for $0<x<0.05$, and finally to a Mott insulator with G-type antiferromagnetic (G-AFM) order for $x\ge 0.05$. The magnetic state switching from the AFM-b to the G-AFM occurs in the weakly localized state near $x=0.03$. We show that such a magnetic transition is controlled by the charge carrier itinerancy and can be understood in light of competing interactions between FM double exchange and AFM superexchange. An incommensurate component is also observed due to competing magnetic interactions.

The scattering potential of the defects on Ge(001) surfaces is investigated by first-principles methods. The standing wave in the spatial map of the local density of states obtained by wave-function matching is compared to the image of the differential conductance measured by scanning tunneling spectroscopy. The period of the standing wave and its phase shift agree with those in the experiment. It is found that the scattering potential becomes a barrier when the electronegativity of the upper atom of the dimer is larger than that of the lower atom, while it acts as a well in the opposite case.

We report on the photoluminescence (PL) properties of Mg${}_x$Zn${}_{1-x}$O/ZnO heterojunctions grown by plasma-assisted molecular-beam epitaxy. Influence of the applied magnetic field ($B$) on the radiative recombination of the two-dimensional electron gas (2DEG) is investigated up to 54 T. An increase in magnetic field in the range of $B$ ≤ 20 T results in a redshift in the PL. Abrupt lineshape changes in the PL spectra are observed at higher magnetic fields, in correlation with the integer quantum Hall states. We attempt to interpret these features using the conventional model for the 2DEG-related PL based on the transition between the 2DEG and a hole as well as a model taking a bound state effect into account, i.e., a charged exciton. The comparison about the adequateness of these models was made, being in favor of the charged exciton model.

We study single-electron transport through a graphene quantum dot with magnetic adsorbates. We focus on the relation between the spin order of the adsorbates and the linear conductance of the device. The electronic structure of the graphene dot with magnetic adsorbates is modeled through numerical diagonalization of a tight-binding model with an exchange potential. We consider several mechanisms by which the adsorbate magnetic state can influence transport in a single-electron transistor: tuning the addition energy, changing the tunneling rate, and in the case of spin-polarized electrodes, through magnetoresistive effects. Whereas the first mechanism is always present, the others require that the electrode has to have either an energy- or spin-dependent density of states. We find that graphene dots are optimal systems to detect the spin state of a few magnetic centers.

The mean-field Hubbard model is used to investigate the formation of the antiferromagnetic phase in hexagonal graphene rings with inner zigzag edges. The outer edge of the ring was taken to be either zigzag or armchair, and we found that both types of structures can have a larger antiferromagnetic interaction as compared with hexagonal dots. This difference could be partially ascribed to the larger number of zigzag edges per unit area in rings than in dots. Furthermore, edge states localized on the inner ring edge are found to hybridize differently than the edge states of dots, which results in important differences in the magnetism of graphene rings and dots. The largest staggered magnetization is found when the outer edge has a zigzag shape. However, narrow rings with armchair outer edge are found to have larger staggered magnetization than zigzag hexagons. The edge defects are shown to have the least effect on magnetization when the outer ring edge is armchair shaped.

Evolutionary structure searches are used to predict stable phases with unique stoichiometries in the hydrogen-rich region of the magnesium/hydrogen phase diagram under pressure. MgH${}_4$, MgH${}_{12}$, and MgH${}_{16}$ are found to be thermodynamically stable with respect to decomposition into MgH${}_2$ and H${}_2$ near 100 GPa, and all lie on the convex hull by 200 GPa. MgH${}_4$ contains two H${}^{-}$ anions and one H${}_2$ molecule per Mg${}^{2+}$ cation, whereas the hydrogenic sublattices of MgH${}_{12}$ and MgH${}_{16}$ are composed solely of H${}_2^{\delta -}$ molecules. The high-hydrogen content stoichiometries have a large density of states at the Fermi level, and the $T_c$ of MgH${}_{12}$ at 140 GPa is calculated to be nearly three times greater than that of the classic hydride, MgH${}_2$, at 180 GPa.

Fe-phthalocyanine (FePc) molecules bonded to metal surfaces form rehybridized interface states involving the Fe central atom reflected in changes of orbital and spin configuration. X-ray absorption spectroscopy and x-ray magnetic circular dichroism show the ferromagnetic coupling of the FePc molecules that are in contact with the Co(001) surface, even at room temperature (300 K), while the overgrown parallel layers of FePc in thicker molecular films are decoupled from the interface. The magnetized interface molecular layer reproduces the magnetic structures of the substrate (domains, patterns).

We present results on the longitudinal spin Seebeck effect (LSSE) shown by semiconducting ferrimagnetic NiFe${}_2$O${}_4$/Pt films from room temperature down to 50 K base temperature. The temperature dependence of the conductivity has been studied in parallel to obtain information about the origin of the electric potentials detected at the Pt coverage of the ferrimagnet in order to distinguish the LSSE from the anomalous Nernst effect. Furthermore, the dependence of the LSSE on temperature gradients as well as the influence of an external magnetic field direction is investigated.

The diluted magnetic semiconductor (Ga,Mn)As is investigated with respect to its damping behavior using frequency dependent ferromagnetic resonance techniques. In particular we investigate the homogeneity of the spin relaxation mechanisms from a submicrometer length scale to several millimeters using time-resolved scanning Kerr microscopy in combination with ferromagnetic resonance. We find magnetic inhomogeneities on submillimeter and submicrometer length scales which lead to artificially broadened ferromagnetic resonance (FMR) lines in conventional experiments.

We explore the linear and nonlinear dynamic regimes of micrometer-scale soft magnetic squares with an in-plane uniaxial anisotropy, recording the response of the magnetization in the spatial domain under a continuous sinusoidal excitation with time-resolved scanning transmission x-ray microscopy. Increasing the excitation field amplitude leads to the dynamic stabilization of nonequilibrium domain configurations, which appear at threshold amplitudes and return to the equilibrium configuration when the amplitude is reduced. On imaging the magnetization in the transition region between two stable magnetic configurations, we observe small domains originating from the vortex core. Dynamic micromagnetic simulations of the domain configuration provide qualitative agreement with the experimental data and insight into the energy dissipation and spin wave contributions.