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The availability of large high-quality single crystals is an important prerequisite for many studies in solid-state research. The optical floating-zone technique is an elegant method to grow such crystals, offering potential to prepare samples that may be hardly accessible with other techniques. As elaborated in this report, examples include single crystals with intentional compositional gradients, deliberate off-stoichiometry, or complex metallurgy. For the cubic chiral magnets Mn$_{1-x}$Fe$_{x}$Si and Fe$_{1-x}$Co$_{x}$Si, we prepared single crystals in which the composition was varied during growth from $x = 0 - 0.15$ and from $x = 0.1 - 0.3$, respectively. Such samples allowed us to efficiently study the evolution of the magnetic properties as a function of composition, as demonstrated by means of neutron scattering. For the archetypical chiral magnet MnSi and the itinerant antiferromagnet CrB$_{2}$, we grew single crystals with varying initial manganese (0.99 to 1.04) and boron (1.95 to 2.1) content. Measurements of the low-temperature properties addressed the correlation between magnetic transition temperature and sample quality. Furthermore, we prepared single crystals of the diborides ErB$_{2}$, MnB$_{2}$, and VB$_{2}$. In addition to high vapor pressures, these materials suffer from peritectic formation, potential decomposition, and high melting temperature, respectively., Comment: 16 pages, 13 figures

Although Mn-Ga alloys are discussed as novel permanent magnetic materials, there are several drawbacks, including the high price of Ga and the yet too small saturation magnetization to name a few. We used several guidelines to motivate the replacement of Ga by Sn to tackle these issues and explored the phase formation, structural and magnetic properties of a Mn 2.6 Ga 1− x Sn x alloy series. The structure of Sn-rich samples is dominated by the corresponding hexagonal and orthorhombic phases, while the structure of Ga-rich samples shows additional contributions from the tetragonal DO 22 structure. However, formation of the tetragonal phase happens only upon an appropriate annealing procedure. In contrast to the discussion in the literature, our experiments do not hint on the tetragonal DO 22 structure being metastable, but rather indicate the DO 22 structure being an equilibrium phase. In general, the experimentally found phase fractions impact on the magnetic properties and hard magnetic properties are downgraded very rapidly even if only a small amount of Ga is substituted by Sn. This indicates that the DO 22 phase found only in the Ga-rich samples is indeed the one which is most relevant for realization of high magnetic anisotropy.

Solid state single crystal growth (SSCG) is a crystal growth technique where crystals are grown from a polycrystalline matrix. Here, we present single crystals of the iron pnictide LaFeAsO grown via SSCG using NaAs as a liquid phase to aid crystallization. The size of the as-grown crystals are up to 2 × 3 × 0.4 mm 3 . Typical for this method, but very uncommon for crystals of the pnictide superconductors and especially for the oxypnictides, the crystals show pronounced facets caused by considerable growth in c direction. The crystals were characterized regarding their composition, structure, magnetic, and thermodynamic properties. This sets the stage for further measurements for which single crystals are crucial such as any c axis and reciprocal space dependent measurements.

The TSFZ growth of Nd-substituted LSCO (La1.81-xNdxSr0.19CuO4, x = 0 ÷ 0.4) single crystals has been explored for the first time. Optimal growth parameters have been determined: oxygen pressure 5.5–6.5 bar; CuO-poor solvent (66 mol.% CuO) and growth rate 0.6 mm/hour. As a result, high quality single crystals with composition La1.81-xSr0.19NdxCuO4 (x = 0, 0.2, 0.3, 0.4) have been successfully grown and characterized by optical polarized microscopy, x-ray diffraction and energy dispersive x-ray spectroscopy analysis. Substitution of La3+ with smaller Nd3+ ions leads to a gradual decrease of lattice parameters as well as of the superconducting transition temperature from 29.5 K for x = 0 to 14.6 K for x = 0.4.

Chemical and structural phase compositions of two single-crystalline samples prepared with different cooling rates from stoichiometric FeTe 0.6 Se 0.4 melts were studied. Both types of samples were investigated in a very comprehensive way using magnetic and electrical transport measurements combined with X-ray, neutron and electron backscatter diffraction. We show that slowly cooled samples are homogeneous on a microscopic scale with only a small excess of iron. Those slowly cooled samples do not exhibit bulk superconductivity down to 1.8 K. In contrast, fast-cooled samples are superconducting below about 14 K but are composed of several chemical phases: they consist of a matrix preserving the crystal structure of slow-cooled samples, and of core-shell structured dendritic inclusions (about 20–30 vol%). These have different crystal structures and chemical compositions and order magnetically at temperatures far above the superconducting transition temperature of the inhomogeneous samples. These structural and chemical inhomogeneities seem to play a vital role in the superconducting properties of this and similar iron-based systems as they lead to internal stress and act in a similar way as the application of the external pressure that reportedly increase the superconducting transition temperature in many iron pnictides and chalcogenides. We argue that a phase pure, homogeneous and stress-free FeTe 0.6 Se 0.4 is non-superconducting.

The nonmagnetic compounds showing extremely large magnetoresistance are attracting a great deal of research interest due to their potential applications in the field of spintronics. ${\mathrm{PtBi}}_{2}$ is one of such interesting compounds showing large linear magnetoresistance (MR) in both the hexagonal and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy and density functional theory calculations to understand the mechanism of liner MR observed in the layered ${\mathrm{PtBi}}_{2}$. Our results uncover linear dispersive surface Dirac states at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point, crossing the Fermi level with a node at a binding energy of $\ensuremath{\approx}900$ meV, in addition to the previously reported Dirac states at the $\overline{M}$ point in the same compound. We further notice from our dichroic measurements that these surface states show an asymmetric spectral intensity when measured with left and right circularly polarized light, hinting at a substantial spin polarization of the bands. Following these observations, we suggest that the linear dispersive Dirac states at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ and $\overline{M}$ points are likely to play a crucial role for the linear field dependent magnetoresistance recorded in this compound.

Recently, the iridate double perovskite ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ has attracted considerable attention due to the report of unexpected magnetism in this ${\mathrm{Ir}}^{5+}$ $(5{d}^{4})$ material, in which according to the ${J}_{\mathrm{eff}}$ model, a nonmagnetic ground state is expected. However, in recent works on polycrystalline samples of the series ${\mathrm{Ba}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{YIrO}}_{6}$ no indication of magnetic transitions have been found. We present a structural, magnetic, and thermodynamic characterization of ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. As determined by x-ray diffraction, the ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ single crystals have a cubic structure, with space group $Fm\overline{3}m$. In agreement with the expected nonmagnetic ground state of ${\mathrm{Ir}}^{5+}$ $({5d}^{4})$ in ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$, no magnetic transition is observed down to 430 mK. Moreover, our results suggest that the low-temperature anomaly observed in the specific heat is not related to the onset of long-range magnetic order. Instead, it is identified as a Schottky anomaly caused by paramagnetic impurities present in the sample, of the order of $n\ensuremath{\sim}0.5(2)%$. These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

We report the structural, magnetic, and thermodynamic properties of the double perovskite compound ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ from x-ray, neutron diffraction, neutron depolarization, $\mathit{dc}$ magnetization, $\mathit{ac}$ susceptibility, specific heat, muon-spin-relaxation $(\ensuremath{\mu}\mathrm{SR})$, electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below $\ensuremath{\sim}113$ K, short-range spin-spin correlations occur within the ${\mathrm{Cu}}^{2+}$ sublattice. With decreasing temperature, the ${\mathrm{Ir}}^{4+}$ sublattice is progressively involved in the correlation process. Below $T=74$ K, the magnetic sublattices of Cu (spin $\mathit{s}=\frac{1}{2}$) and Ir (pseudospin $\mathit{j}=\frac{1}{2}$) in ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ are strongly coupled and exhibit an antiferromagnetic phase transition into a noncollinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in $\mathit{ac}$ susceptibility as well as in the NMR and $\ensuremath{\mu}\mathrm{SR}$ spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled $5\mathit{d}$ ion ${\mathrm{Ir}}^{4+}$. We argue that the rich magnetic behavior observed in ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ is related to complex magnetic interactions between the strongly correlated spin-only $3\mathit{d}$ ions with the strongly spin-orbit coupled $5\mathit{d}$ transition ions where a combination of the spin-orbit coupling and the low symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.

Materials with a $5{d}^{4}$ electronic configuration are generally considered to have a nonmagnetic ground state ($J=0$). Interestingly, ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ (${\mathrm{Ir}}^{5+}$ having $5{d}^{4}$ electronic configuration) was recently reported to exhibit long-range magnetic order at low temperature and the distorted ${\mathrm{IrO}}_{6}$ octahedra were discussed to cause the magnetism in this material. Hence, a comparison of structurally distorted ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ with cubic ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$ may shed light on the source of magnetism in such ${\mathrm{Ir}}^{5+}$ materials with $5{d}^{4}$ configuration. Besides, ${\mathrm{Ir}}^{5+}$ materials having $5{d}^{4}$ are also interesting in the context of recently predicted excitonic types of magnetism. Here we report a single-crystal-based analysis of the structural, magnetic, and thermodynamic properties of ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$. We observe that in ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$ for temperatures down to 0.4 K, long-range magnetic order is absent but at the same time correlated magnetic moments are present. We show that these moments are absent in fully relativistic ab initio band-structure calculations; hence, their origin is presently unclear.

We present properties of single crystals of the iron pnictide superconductor RbFe2As2 grown using a self-flux method. A bulk superconducting transition at Tc ∼2.6 K was consistently observed in resistivity, magnetic susceptibility, and specific heat measurements. While the resistivity behaves like a conventional metal at low T, the magnetic susceptibility shows an unusual broad maximum around 80 K in the normal state. A large Sommerfeld coefficient, γ0=127mJ/mol K2, was observed seemingly a common feature of heavily hole-doped “122” compounds. In the superconducting state, we analyzed our specific heat data based on the s- and d-wave two-gap models. The presence of the small gap with 2Δ1(0)/kBTc