Alternating magnetic anisotropy of Li2_2(Li1−xTx_{1-x}T_x)N with TT = Mn, Fe, Co, and Ni

Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$ easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co $\rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.Comment: 5 pages, 3 figures, published as PRB Rapid Communication, Fig. 3 update

Dramatic Changes in the Electronic Structure Upon Transition to the Collapsed Tetragonal Phase in CaFe2As2

We use angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations to study the electronic structure of CaFe$_2$As$_2$ in previously unexplored collapsed tetragonal (CT) phase. This unusual phase of the iron arsenic high temperature superconductors was hard to measure as it exists only under pressure. By inducing internal strain, via the post growth, thermal treatment of the single crystals, we were able to stabilize the CT phase at ambient-pressure. We find significant differences in the Fermi surface topology and band dispersion data from the more common orthorhombic-antiferromagnetic or tetragonal-paramagnetic phases, consistent with electronic structure calculations. The top of the hole bands sinks below the Fermi level, which destroys the nesting present in parent phases. The absence of nesting in this phase along with apparent loss of Fe magnetic moment, are now clearly experimentally correlated with the lack of superconductivity in this phase.Comment: 5 pages, 4 figures, accepted in PRB(RC

Unusual temperature dependence of band dispersion in Ba(Fe(1-x)Ru(x))2As2 and its consequences for antiferromagnetic ordering

We have performed detailed studies of the temperature evolution of the electronic structure in Ba(Fe(1-x)Ru(x))2As2 using Angle Resolved Photoemission Spectroscopy (ARPES). Surprisingly, we find that the binding energy of both hole and electron bands changes significantly with temperature in pure and Ru substituted samples. The hole and electron pockets are well nested at low temperature in unsubstituted (BaFe2As2) samples, which likely drives the spin density wave (SDW) and resulting antiferromagnetic order. Upon warming, this nesting is degraded as the hole pocket shrinks and the electron pocket expands. Our results demonstrate that the temperature dependent nesting may play an important role in driving the antiferromagnetic/paramagnetic phase transition.Comment: 5 pages, 6 figure

Optical and magneto-optical properties of RFe2 (R=Gd,Tb,Ho,Lu) and GdCo2

The conductivity tensors of single crystals and polycrystals of RFe2 (R=Gd,Tb,Ho,Lu) and GdCo2 were determined in the visible and near UV ranges. The magneto-optical Kerr effect (MOKE) was studied at different temperatures and magnetic fields. The single-crystal data show more features and larger magnitudes in the MOKE spectrum than the polycrystalline data under the same experimental conditions. The theoretical optical conductivity tensors for these compounds were calculated using the tight-binding linear-muffin-tin orbital (TB-LMTO) method in the local spin-density approximation. The agreement between theory and experiment was poor except for LuFe2, in which the 4f shell is completely closed

Ellipsometric and Kerr-effect studies of Pt3−X (X=Mn,Co)

The conductivity tensor of polycrystalline Pt3X (X=Mn,Co) was determined between 1.6 and 5.2 eV. Samples were arc melted, mechanically polished, and annealed at 500°C for 1 h in Ar. The complex dielectric function was measured from 1.3 to 5.2 eV at room temperature with a rotating analyzer ellipsometer. The magneto-optic Kerr effect was studied between 10 and 293 K in magnetic fields up to 3 T. We used the tight-binding linear-muffin-tin-orbital method in the local spin-density approximation to determine the band structure, density of states, and optical conductivity. Including an empirical quasiparticle self-energy and a lifetime broadening yields good agreement of experimental and calculated spectra

Observation of a metamagnetic phase transition in an itinerant 4f system via the magneto-optic Kerr effect: Ce(Fe1−xCox)2

The optical and magneto-optical properties of single crystals of YFe2, CeFe2, and Ce(Fe1−xCox)2 (x≃0.1) were measured between 1.4 and 5.0 eV using a rotating-analyzer ellipsometer and a normal-incidence polar Kerr spectrometer. The electronic structures and optical properties of YFe2 and CeFe2 were calculated using the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation. For YFe2 the calculations reproduce the experimental spectra. Alloying CeFe2 with small amounts of Co leads to an electronic instability which is evidenced by a low-temperature antiferromagnetic (AF) phase. The Kerr effect was measured in the AF and field-induced ferromagnetic (FM) regime. A remarkably large Kerr rotation was measured even in the AF state (up to −1°). The phase transition from AF to FM order was observed in the Kerr rotation spectra at 5 and 50 K at photon energies of 1.8 and 4.0 eV

Optical properties and electronic structure of single crystals of LuAl2 and YbAl2

The optical conductivities of single crystals of LuAl2 and YbAl2 were measured by spectroscopic ellipsometry in the energy range of 1.4–5.5eV for LuAl2 and 1.4–5.2eV for YbAl2. The optical conductivity spectra of LuAl2 and YbAl2 show similar features except for a difference in magnitude. Both have peaks near 1.8–2.1eV and broad shoulders between 3.0 and 4.0eV. The shoulder is weaker in YbAl2. The band structure, density of states, and optical conductivity were calculated with the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. The calculated optical conductivity with the inclusion of energy-dependent broadening agrees well with the experimental data. Oxidation effects on the surface of the sample were modeled using a three-phase model. The calculated optical conductivity of the clean surface is enhanced over that of the oxidized surface

Molecular Dynamics Simulation of Sympathetic Crystallization of Molecular Ions

It is shown that the translational degrees of freedom of a large variety of molecules, from light diatomic to heavy organic ones, can be cooled sympathetically and brought to rest (crystallized) in a linear Paul trap. The method relies on endowing the molecules with an appropriate positive charge, storage in a linear radiofrequency trap, and sympathetic cooling. Two well--known atomic coolant species, ${}^9{\hbox{Be}}^+$ and ${}^{137}{\hbox{Ba}}^+$, are sufficient for cooling the molecular mass range from 2 to 20,000 amu. The large molecular charge required for simultaneous trapping of heavy molecules and of the coolant ions can easily be produced using electrospray ionization. Crystallized molecular ions offer vast opportunities for novel studies.Comment: Accepted for publication in Phys. Rev.

Emerging Digital Frontiers for Service Innovation

This paper examines emerging digital frontiers for service innovation that a panel discussed at a workshop on this topic held at the 48th Annual Hawaii International Conference on System Sciences (HICSS). The speakers and participants agreed that that service systems are fundamental for service innovation and value creation. In this context, service systems are related to cognitive systems, smart service systems, and cyber-physical systems and depend on the interconnectedness among system components. The speakers and participants regarded humans as the central entity in all service systems. In addition, data, they saw personal data in particular as key to service systems. They also identified several challenges in the areas of cognitive systems, smart service systems, cyber-physical systems, and human-centered service systems. We hope this workshop report helps in some small way to cultivate the emerging service science discipline and to nurture fruitful discussions on service innovation