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The unexpected colours of layered sulfides are investigated using spectroscopy and a theoretical defect model approach.

The exact and precise determination of the boron concentration in silicon is still a challenge. A systematic investigation dealing with the digestions of 60 silicon samples with HF-HNO3 and subsequent boron determination by ICP-OES revealed that the concentration found could be up to 60% lower than the actual boron concentration depending on the composition of the sample solution. As the original boron–silicon compound that was identified was colloidally precipitated in the presence of an excess of hydrofluoric acid and then partially retained by filtration or by the sample introduction system, systematic lower boron concentrations were determined. In acidic, HF-free digestion solutions, this compound existed in a soluble form parallel to the borate in B(OH)4−. In an excess of hydrofluoric acid, the compound was converted into the colloidal form and, in parallel, B(OH)4− was converted to tetrafluoroborate, BF4−. For the composition of the colloidal compound, a molar ratio of boron to silicon of 1 : 4 could be determined. 11B-ss-NMR analysis revealed a tetrahedral geometry compound with a central boron atom surrounded by four silicon atoms. It is assumed that a soluble form with four –Si(OH)3 groups was present in the hydrofluoric acid-free solutions, while an insoluble form with four –SiF3 groups was present in HF-containing solution.

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen--Cooper--Schrieffer (BCS) pairing and the strongly coupled Bose--Einstein condensation (BEC). We report on $^{77}$Se nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the $c$ axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime., Comment: 6 pages, 4 figures

In this work we revisit the phase diagram of Co-doped LaFeAsO using single crystals and thermodynamic methods. From magnetic susceptibility studies, we track the doping evolution of the antiferromagnetic phase to reveal a continuous suppression of ${T}_{\mathrm{N}}$ up to 5% Co doping. To study the evolution of the so-called nematic phase, the temperature dependence of the length changes along the $a$ and $b$ orthorhombic directions, $\mathrm{\ensuremath{\Delta}}L/{L}_{0}$, was determined by high-resolution capacitance dilatometry. The results clearly show a gradual reduction of the orthorhombic distortion $\ensuremath{\delta}$ and of ${T}_{\mathrm{S}}$ with increasing Co content up to 4.5%, while it is completely suppressed for 7.5% Co. Bulk superconductivity was found in a small doping region around 6% Co content, while both ${T}_{\mathrm{c}}$ and the superconducting volume fraction rapidly drop in the neighboring doping regime. Ultimately, no microscopic coexistence between the superconducting and magnetic phases can be assessed within our resolution limit, in sharp contrast with other iron-pnictide families, e.g., electron- and hole-doped ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$.

We determine the phase diagram of ${\mathrm{LaFe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{AsO}$ single crystals by using nuclear magnetic resonance (NMR). Up to a nominal doping of $x=0.03$, it follows the phase diagram for F-doped polycrystals. Above $x=0.03$, the F-doped samples become superconducting, whereas for Co doping the structural and magnetic transitions can be observed up to $x=0.042$, and superconductivity occurs only for higher doping levels and with reduced transition temperatures. For dopings up to $x=0.056$, we find evidence for short-range magnetic order. By means of relaxation-rate measurements, we map out the magnetic fluctuations that reveal the interplay of nematicity and magnetism. Above the nematic ordering, the spin fluctuations in ${\mathrm{LaFe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{AsO}$ are identical to those in $\mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x})}_{2}{\mathrm{As}}_{2}$, suggesting that nematicity in LaFeAsO is a result of the fluctuating spin density wave as well.

We present $^{75}\mathrm{As}$ nuclear magnetic and quadrupole resonance results (NMR, NQR) on a new set of $\mathrm{La}\mathrm{Fe}\mathrm{As}{\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}$ polycrystalline samples. Improved synthesis conditions led to more homogenized samples with better control of the fluorine content. The $\mathrm{structural}\ensuremath{\equiv}\mathrm{nematic}$, magnetic, and superconducting transition temperatures have been determined by NMR spin-lattice relaxation rate and AC susceptibility measurements. The so-determined phase diagram deviates from the published one, especially for low F-doping concentrations. However, if the doping level is determined from the NQR spectra, both phase diagrams can be reconciled. The absence of bulk coexistence of magnetism and superconductivity and a nanoscale separation into low-doping-like and high-doping-like regions have been confirmed. Additional frequency-dependent intensity, spin-spin, and spin-lattice relaxation rate measurements on underdoped samples at the boundary of magnetism and superconductivity indicate that orthorhombicity and magnetism originate from the low-doping-like regions, and superconductivity develops first in the high-doping-like regions.

We report a systematic elastoresistivity study on ${\mathrm{LaFe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{AsO}$ single crystals, which have well separated structural and magnetic transition lines. All crystals show a Curie-Weiss--like nematic susceptibility in the tetragonal phase. The extracted nematic temperature is monotonically suppressed upon cobalt doping, and changes sign around the optimal doping level, indicating a possible nematic quantum critical point beneath the superconducting dome. The amplitude of the nematic susceptibility shows a peculiar double-peak feature. This could be explained by a combined effect of different contributions to the nematic susceptibility, which are amplified at separated doping levels of ${\mathrm{LaFe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{AsO}$.

We derive the normalized limit of detection for frequency space ( nLOD f ) as a parameter to measure the sensitivity of an NMR spectroscopy setup. nLOD f is independent of measurement settings such as bandwidth or number of measurement points, and allows to compare performances of different setups. We demonstrate the usefulness of the new nLOD f by comparing the sensitivity of NMR setups from various publications, which all use microcoils. Finally, we want to propose a standard measurement and report format for the sensitivity of new NMR setups.

The compound InCu${}_{2/3}$V${}_{1/3}$O${}_{3}$ is a rare realization of the quasi-two-dimensional (2D) honeycomb spin lattice with XY anisotropy and strongly frustrated interlayer coupling. Despite substantial interest, its ground state has not been unambiguously identified. The authors, using NQR, NMR, and \ensuremath{\mu}SR spectroscopies and theoretical calculations, have ultimately settled the existing controversies. They find evidence for a quasi-2D static antiferromagnetic state below 39 K gradually transforming into a 3D N\'eel state at 15 K. Interestingly, signatures of the topological Berezinsky-Kosterlitz-Thouless transition were observed in the 2D regime of this compound.

We report a systematic elastoresistivity study on LaFe_{1-x}Co_{x}AsO single crystals, which have well separated structural and magnetic transition lines. All crystals show a Curie-Weiss-like nematic susceptibility in the tetragonal phase. The extracted nematic temperature is monotonically suppressed upon cobalt doping, and changes sign around the optimal doping level, indicating a possible nematic quantum critical point beneath the superconducting dome. The amplitude of the nematic susceptibility shows a peculiar double-peak feature. This could be explained by a combined effect of different contributions to the nematic susceptibility, which are amplified at separated doping levels of LaFe_{1-x}Co_{x}AsO.

We present a study of parameter optimization for synthesizing truly stoichiometric polycrystalline LiFeAs. Stoichiometric LiFeAs has been prepared in a very broad range of synthesis temperature (200–900 °C) under otherwise exactly the same conditions, and has been characterized by structural, magnetic, transport, nuclear quadrupole resonance (NQR), and specific heat measurements. Our study showed that the LiFeAs phase is formed at 200 °C with a large amount of impurity phases. The amount of these impurity phases reduces with increasing synthesis temperature and the clean LiFeAs phase is obtained at a synthesis temperature of 600 °C. Magnetic susceptibility and resistivity measurements confirmed that the superconducting properties such as the critical temperature T c , and the upper critical field H c2 do not depend on the synthesis temperature (≤ 700 °C), remaining at almost the same value of ∼19 K and ∼40 T, respectively. However, the width ΔT c of the transition and the NQR line width decrease with increasing the synthesis temperature and reached to minimum value for the synthesis temperature of 600 °C. Our careful analysis suggests that the best sample obtained at 600 °C is optimal concerning the low resistivity, high residual resistivity ratio ( RRR ), low ΔT c , high T c and H c2 , and a small NQR line width with values which are comparable to that reported for LiFeAs single crystals. Specific heat measurements confirmed the bulk superconducting nature of the samples. The H c2 value estimated from the specific heat is consistent with that of the resistivity measurements. Concisely, 600 °C synthesis temperature yields optimal high quality polycrystalline LiFeAs bulk samples. Further improvement of the quality of the sample prepared at 600 °C could be obtained by a controlled slow cooling process. Microstructural analysis reveals that the abundance of micro-cracks becomes strongly reduced by the slow cooling process, resulting in an increase in clean and well-connected grain boundaries.

BaAg2Cu[VO4]2 contains Cu(II) S=1/2 ions on a distorted two-dimensional triangular lattice interconnected via non-magnetic [VO4] entities. DFT band structure calculations, quantum Monte-Carlo simulations, and high-field magnetization measurements show that the magnetism of this compound is determined by a superposition of ferromagnetic (FM) and antiferromagnetic (AFM) uniform spin-1/2 chains with nearest neighbor exchange couplings of J FM=−19 K and J AFM=9.5 K (A. Tsirlin, A. Möller, B. Lorenz, Y. Skourski, H. Rosner, Phys. Rev. B 85 (2012) 014401). Here we report the study of BaAg2Cu[VO4]2 by high-field/frequency electron spin resonance (HF-ESR) and nuclear magnetic resonance (NMR) spectroscopies, which probe the local magnetic properties. In the HF-ESR measurements, we observe an anisotropic ESR spectrum typical for the Cu(II) ions and determine the g-tensor, g ||=2.38 and g ⊥=2.06. Moreover, we see a substantial change in the spectral shape of the ESR lines at low temperatures indicating the presence of short range magnetic correlations. The analysis of the low-temperature ESR spectra shows that its peculiar structure is due to the development of the anisotropic internal fields corresponding to FM and AFM correlations in the respective Cu spin chains. In the NMR spectra the signals from 51V nuclei in the two types of chains were identified. The analysis of the temperature evolution of these signals strongly supports the ESR findings on the occurrence of two types of Cu chains. Altogether, the HF-ESR and NMR results confirm theoretical predictions of the superposition of FM and AFM Cu(II) spin-1/2 chains in the studied material.

Herein, we present the effect of the nanoconfinement of LiBH 4 within porous aerogel-like carbon on its hydrogen storage properties. The carbon scaffold is prepared by salt templating – a facile and sustainable technique for the production of micro- and mesoporous carbon-based materials. A loading of up to 40 wt. % of LiBH 4 is achieved by melt infiltration, and the hydride remains amorphous as shown by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning transmission electron microscopy (STEM). Simultaneous thermogravimetry and mass spectroscopy (TG-MS) reveal that the nanoconfined LiBH 4 starts to desorb hydrogen already at 200 °C with the main release at 310 °C. A partial rehydrogenation at moderate conditions (100 bar and 300 °C) is demonstrated. In contrast to recent reports, in-situ heating in the transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) indicate that both decomposition products (B and LiH) remain within the carbon pores. Nuclear magnetic resonance (NMR) measurements reveal the presence of amorphous and partially oxidized boron in the dehydrogenated sample that may impede the reversibility of the (de)hydrogenation process.

Two novel compounds, LiCu Ch ( Ch = Se or Te), were synthesized by direct reaction between elements in closed ampules inside corundum crucibles. Both compounds are highly air-sensitive and possess an anti-PbClF crystal structure, which contains Cu Ch layer analogues to the Fe[As/Se] layers in Fe-based superconductors. In electrochemical battery cells, Li can be almost completely extracted from LiCuSe, but the reverse reaction is only partly successful and Li2Se and Cu2- xSe are formed instead. LiCuSe exhibits a temperature independent and slightly positive magnetic susceptibility. From 7Li NMR measurements, the activation energy of the Li ion diffusion process is about 0.5 eV but is slightly lower for LiCuTe as compared to LiCuSe. Also, the small and almost temperature independent NMR shifts of the 7Li nucleus indicate the absence of Pauli paramagnetism in these compounds, consistent with a 3 d10 full valence state of the Cu ions.

We report $^{75}\mathrm{As}$ nuclear magnetic resonance measurements on single crystals of ${\mathrm{RbFe}}_{2}{\mathrm{As}}_{2}$ and ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$. Taking previously reported results for ${\mathrm{KFe}}_{2}{\mathrm{As}}_{2}$ into account, we find that the anisotropic electronic correlations evolve towards a magnetic instability in the $A{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ series (with $A=\mathrm{K}$, Rb, Cs). Upon isovalent substitution with larger alkali-metal ions, a drastic enhancement of the anisotropic nuclear spin-lattice relaxation rate and decreasing Knight shift reveal the formation of pronounced spin fluctuations with stripe-type modulation. Furthermore, a decreasing power-law exponent of the nuclear spin-lattice relaxation rate ${(1/{T}_{1})}_{H\ensuremath{\parallel}ab}$, probing the in-plane spin fluctuations, evidences an emergent deviation from Fermi-liquid behavior. All these findings clearly indicate that the expansion of the lattice in the $A{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ series tunes the electronic correlations towards a quantum critical point at the transition to a yet unobserved ordered phase.

We discuss the impact of concomitant substitution of Fe by Mn and La by Y in optimally F-doped ${\mathrm{LaFeAsO}}_{0.89}{\mathrm{F}}_{0.11}$. Mn has a known poisoning effect on superconductivity which is particularly strong in the La1111 system, where 0.2% of Mn were reported to completely suppress superconductivity. Through isovalent substitution of La by the much smaller Y we are able to inflict chemical pressure on the structure, which we show is stabilizing the superconducting state, resulting in a drastically larger amount of Mn needed to completely quench superconductivity. Interestingly, we find that the lattice parameter $\mathit{c}$ changes significantly even for small amounts of Mn substitution within a series, which is unexpected taking only the differences between ionic radii into account. We discuss our findings in the light of electron localization caused by small amounts of paramagnetic Mn impurities in ${\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Y}}_{y}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{AsO}}_{0.89}{\mathrm{F}}_{0.11}$ also indicated by resistivity and M\"o\ss{}bauer measurements.

The electrochemical characteristics of silicon diphosphide (SiP2) as a new anode material for future lithium-ion batteries (LIBs) are evaluated. The high theoretical capacity of about 3900 mA h g–1 (fully lithiated state: Li15Si4 + Li3P) renders silicon diphosphide as a highly promising candidate to replace graphite (372 mA h g–1) as the standard anode to significantly increase the specific energy density of LIBs. The proposed mechanism of SiP2 is divided into a conversion reaction of phosphorus species, followed by an alloying reaction forming lithium silicide phases. In this study, we focus on the conversion mechanism during cycling and report on the phase transitions of SiP2 during lithiation and delithiation. By using ex situ analysis techniques such as X-ray powder diffraction, formed reaction products are identified. Magic angle spinning nuclear magnetic resonance spectroscopy is applied for the characterization of long-range ordered compounds, whereas X-ray photoelectron spectroscopy gives informat...

The nuclear magnetic resonance (NMR) method was applied for tracking boron impurities in the refining process of metallurgical grade (MG) silicon. From the NMR signal of the 11B isotope at an operating temperature 4.2 K, the boron concentration can be estimated down to the order of 1–10 wppm B. After melting and resolidification of MG-Si alloyed with Ca and Ti, a major fraction of B impurities remains in the Si solid solution as inferred from the characteristic NMR frequency. The alloying element Ti does not form substantial fractions of TiB2. Acid leaching of crushed powders of MG-Si alloyed with Ca and Ti can diminish the initial impurity content of B suggesting its accumulation in the grain boundary phases. NMR signals of TiB2 at 4.2 K and room temperature (RT), and of poly-Si with different B doping at 4.2 K.

We present experimental results of combined electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements on single crystals of the Swedenborgite-type compounds ${\mathrm{YBaCo}}_{3}M{\mathrm{O}}_{7}$ ($M$=Al, Fe). The magnetic lattice of these materials can be described as stacks of strongly geometrically frustrated kagome layers built up of ${\mathrm{Co}}^{2+}$ ($S=3/2$) ions. Due to the Co-$M$ site intermixing, there are $M$-type defects in the kagome planes as well as magnetic Co ions at the interplanar positions. Previous investigations revealed large antiferromagnetic (AFM) Curie-Weiss temperatures in both compounds. Yet no AFM long-range order but a spin glass behavior at low temperatures has been observed. Using $^{27}\mathrm{Al}$ NMR as well as ${\mathrm{Co}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ESR spin probes that are sensitive to local magnetic properties at different crystallographic sites, we have identified two magnetic subsystems in both compounds and have studied their distinct properties. In particular in the case of ${\mathrm{YBaCo}}_{3}{\mathrm{AlO}}_{7}$, we have observed a gradual development of the spin correlations in the two-dimensional (2D) kagome planes containing nonmagnetic Al defects and the establishment of a 3D frozen glasslike spin state of the interplanar Co ions at lower temperatures. We have found that despite a strong dependence of the ordering temperature in the kagome layers on the type of the $M$ ion (magnetic or nonmagnetic), the final 3D static ground state sets in at rather similar temperatures. We argue that the peculiar spin dynamics and a disordered magnetic ground state of the studied compounds result from the interplay of strong magnetic frustration and intrinsic structural disorder arising due to the intersite mixing of Co and $M$ atoms.

The S=1/2 Heisenberg spin chain compound SrCuO2 doped with different amounts of nickel (Ni), palladium (Pd), zinc (Zn) and cobalt (Co) has been studied by means of Cu nuclear magnetic resonance (NMR). Replacing only a few of the S=1/2 Cu ions with Ni, Pd, Zn or Co has a major impact on the magnetic properties of the spin chain system. In the case of Ni, Pd and Zn an unusual line broadening in the low temperature NMR spectra reveals the existence of an impurity-induced local alternating magnetization (LAM), while exponentially decaying spin-lattice relaxation rates $T_1^{-1}$ towards low temperatures indicate the opening of spin gaps. A distribution of gap magnitudes is proven by a stretched spin-lattice relaxation and a variation of $T_1^{-1}$ within the broad resonance lines. These observations depend strongly on the impurity concentration and therefore can be understood using the model of finite segments of the spin 1/2 antiferromagnetic Heisenberg chain, i.e. pure chain segmentation due to S = 0 impurities. This is surprising for Ni as it was previously assumed to be a magnetic impurity with S = 1 which is screened by the neighboring copper spins. In order to confirm the S = 0 state of the Ni, we performed x-ray absorption spectroscopy (XAS) and compared the measurements to simulated XAS spectra based on multiplet ligand-field theory. Furthermore, Zn doping leads to much smaller effects on both the NMR spectra and the spin-lattice relaxation rates, indicating that Zn avoids occupying Cu sites. For magnetic Co impurities, $T_1^{-1}$ does not obey the gap like decrease, and the low-temperature spectra get very broad. This could be related to the increase of the Neel temperature which was observed by recent muSR and susceptibility measurements, and is most likely an effect of the impurity spin $S\neq0$., 14 pages, 10 figures

We present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide information on the nature and suppression of spin fluctuations associated with charge order. We find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.

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.

Using nuclear quadrupole resonance, the phase diagram of $1111 R{\mathrm{FeAsO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}$ ($R=\text{La}$, Ce, Sm) iron pnictides is constructed as a function of the local charge distribution in the paramagnetic state, which features low-doping-like (LD-like) and high-doping-like (HD-like) regions. Compounds based on magnetic rare earths (Ce, Sm) display a unified behavior, and comparison with La-based compounds reveals the detrimental role of static iron $3d$ magnetism on superconductivity, as well as a qualitatively different evolution of the latter at high doping. It is found that the LD-like regions fully account for the orthorhombicity of the system, and are thus the origin of any static iron magnetism. Orthorhombicity and static magnetism are not hindered by superconductivity but limited by dilution effects, in agreement with two-dimensional (2D) (respectively three-dimensional) nearest-neighbor square lattice site percolation when the rare earth is nonmagnetic (respectively magnetic). The LD-like regions are not intrinsically supportive of superconductivity, contrary to the HD-like regions, as evidenced by the well-defined Uemura relation between the superconducting transition temperature and the superfluid density when accounting for the proximity effect. This leads us to propose a complete description of the interplay of ground states in 1111 pnictides, where nanoscopic regions compete to establish the ground state through suppression of superconductivity by static magnetism, and extension of superconductivity by proximity effect.

Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8−xEu0.2SrxCuO4. We use three complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and specific heat—to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order., Understanding of how charge stripe order emerges in cuprates remains elusive. Here, Pelc et al. report the discovery of a charge nematic phase between charge-stripe order and pseudogap state in La1.8-xEu0.2SrxCuO4, resolving the process of charge stripe development in cuprates.

Large and high quality single crystals of the new unconventional superconductor LiFeAs were grown by a new approach using the self-flux technique. Both energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectroscopy revealed a stoichiometric Li/Fe/As composition. Measurements of the magnetic susceptibility reveal the superconducting transition at TC = 17 K with a very sharp ΔTC and a 100% shielding fraction and, thus, bulk superconductivity. This sharp transition is also found by measurements of the specific heat and by measurements of the temperature dependence of the resistivity. Nuclear quadrupole resonance (NQR) spectroscopy reveals a very sharp resonance line, with a much smaller line width than reported for all other FeAs superconductors, confirming the high ordering of the LiFeAs single crystals also on a local scale.

Aims: A carbon-wrapped nanoscaled thermometer for a contactless temperature control in biological systems on the cellular level is presented. Materials & methods: The thermometer is based on multiwalled carbon nanotubes (MWCNTs) filled with materials with strongly temperature-dependent nuclear magnetic resonance (NMR) parameters. The NMR frequency shift and relaxation time were measured in cuprous-iodide-filled CNTs at different temperatures. Results: The experimental data indicate a pronounced temperature dependence of the NMR parameters, thereby realizing the nanoscaled thermometer. Conclusion: This study is a proof-of-concept that the functionalized CNTs can be used as a contactless thermometer in biomedical applications.

We report on a systematic approach to exploit the potential of filled carbon nanotubes (CNT) to act as sensors that might provide non-invasive temperature control in biological systems on a cellular level. In this case the temperature is detected by measuring NMR parameters on the filling materials. The beneficial feature of a carbon nanotube is to provide protection of both (i) a human body against toxic adverse effects from the filling material and (ii) a filling material against chemical and biochemical exposure. The feasibility of this concept has been demonstrated on the example of the temperature-dependent NMR frequency and relaxation time measured on the CNT filled with the appropriate sensor materials.

We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for large fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.

The $S=1/2$ antiferromagnetic Heisenberg spin chain compound ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ doped with $1%$ and $2%$ of Ni impurities has been studied by means of $^{63}\mathrm{Cu}$ nuclear magnetic resonance. A strong decrease of the spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ at low temperatures points toward a spin gap, while a stretching exponent $\ensuremath{\lambda}l1$ and a frequency dependence of ${T}_{1}^{\ensuremath{-}1}$ indicate that this spin gap varies spatially and should rather be characterized as a spin pseudogap. The magnitude of the spin pseudogap scales with doping level. Our results therefore evidence the finite-size character of this phenomenon. Moreover, an unusual narrowing of the low-temperature NMR lines reveals the suppression of the impurity-induced staggered paramagnetic response with increasing doping level.

In this paper we report a detailed $\mu^{+}$SR and {}$^{19}$F-NMR study of the La$_{0.7}$Y$_{0.3}$FeAsO$_{1-x}$F$_{x}$ class of materials. Here, the diamagnetic La$_{1-y}$Y$_{y}$ substitution increases chemical pressure and, accordingly, sizeably enhances the optimal superconducting transition temperature. We investigate the magnetic-superconducting phase transition by keeping the Y content constant ($y = 0.3$) and by varying the F content in the range $0.025 \leq x \leq 0.15$. Our results show how magnetism and superconductivity coexist for $x = 0.065$. Such coexistence is due to segregation of the two phases in macroscopic regions, resembling what was observed in LaFeAsO$_{1-x}$F$_{x}$ materials under applied hydrostatic pressure. This scenario is qualitatively different from the nanoscopic coexistence of the two order parameters observed when La is fully substituted by magnetic rare-earth ions like Sm or Ce.

Trilayered Pd/MnO x /Pd nanomembranes are fabricated as the cathode catalysts for Li-O2 batteries. The combination of Pd and MnO x facilitates the transport of electrons, lithium ions, and oxygen-containing intermediates, thus effectively decomposing the discharge product Li2O2 and significantly lowering the charge overpotential and enhancing the power efficiency. This is promising for future environmentally friendly applications.

We report a combined experimental study of magnetic properties of a single crystal of the frustrated diamond lattice antiferromagnet ${\text{CoAl}}_{2}{\text{O}}_{4}$ with ${\text{Co}}^{2+}$ electron spin resonance, $^{27}\mathrm{Al}$ nuclear magnetic resonance, and muon spin rotation/relaxation techniques. With our local probes, we show that the frustration of spin interactions and the Co/Al site disorder strongly affect the spin dynamics. The experimental results evidence inhomogeneous and slow magnetic fluctuations and the occurrence of short-range electron spin correlations far above a characteristic temperature ${T}^{*}=8$ K at which the spin system turns into in a quasistatic state. Our data indicate that this spin order is likely short range and unconventional with spin fluctuations persistent even at $T\ensuremath{\ll}{T}^{*}$. The results of three spectroscopy techniques highlight a nontrivial role of structural disorder for the magnetism of a frustrated diamond spin lattice at the proximity to the critical point.

We report $^{63}$Cu nuclear magnetic resonance and muon spin rotation measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound Sr$_{1.9}$Ca$_{0.1}$CuO$_3$. An exponentially decreasing spin-lattice relaxation rate 1/T$_1$ indicates the opening of a spin gap. This behavior is very similar to what has been observed for the cognate zigzag spin chain compound Sr$_{0.9}$Ca$_{0.1}$CuO$_2$, and confirms that the occurrence of a spin gap upon Ca doping is independent of the interchain exchange coupling $J'$. Our results therefore generally prove the appearance of a spin gap in an antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the intrachain exchange coupling $J$. A low temperature upturn of 1/T$_1$ evidences growing magnetic correlations. However, zero field muon spin rotation measurements down to 1.5 K confirm the absence of magnetic order in this compound which is most likely suppressed by the opening of the spin gap.

We report $^{7}$Li, $^{29}$Si, and $^{13}$C NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei at room temperature, we find that only the $^{13}$C spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature and Larmor frequency ($\omega_L$) dependences of the $^7$Li linewidth and spin-lattice relaxation rates $T_1^{-1}$ are described by an activated law with the activation energy $E_A$ of 0.31 eV and the correlation time $\tau_0$ in the high temperature limit of 1.3 ps. The $3/2$ power law dependence of $T_1^{-1}$ on $\omega_L$ which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the $\mu$s timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate $T_{1\rho}^{-1}$ results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes., Comment: 28 pages with double line spacing, 7 figures and 2 tables, accepted version in Journal of Power Sources

The synthesis, structure, and elementary magnetic and electronic properties are reported for layered compounds of the type Na3-xMIr2O6 and Na3-xM2IrO6, where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn). The rhombohedral structures, in space group R-3m, were determined by refinement of neutron and synchrotron powder diffraction data. No clear evidence for long range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder diffraction patterns except in the case of M = Zn, thus in general the compounds are best designated as sodium deficient {\alpha}-NaFeO2-type phases with formulas Na1-xM1/3Ir2/3O2 or Na1-xM2/3Ir1/3O2. Synchrotron powder diffraction patterns indicate that several of the compounds likely have honeycomb in-plane metal-iridium ordering with disordered stacking of the layers. All the compounds are sodium deficient under our synthetic conditions and are black and insulating. Weiss constants derived from magnetic susceptibility measurements indicate that Na0.62Mn0.61Ir0.39O2, Na0.80Fe2/3Ir1/3O2, Na0.92Ni1/3Ir2/3O2, Na0.86Cu1/3Ir2/3O2, and Na0.89Zn1/3Ir2/3O2 display dominant antiferromagnetic interactions. For Na0.90Co1/3Ir2/3O2 the dominant magnetic interactions at low temperature are ferromagnetic while at high temperatures they are antiferromagnetic; there is also a change in the effective moment. Low temperature specific heat measurements (to 2 K) on Na0.92Ni1/3Ir2/3O2 indicate the presence of a broad magnetic ordering transition. X-ray absorption spectroscopy shows that iridium is at or close to the 4+ oxidation state in all compounds. 23Na nuclear magnetic resonance measurements comparing Na2IrO3 to Na0.92Ni1/3Ir2/3O2 and Na0.89Zn1/3Ir2/3O2 provide strong indications that the electron spins are short-range ordered in the latter two materials. All of the compounds are spin glasses., Comment: Journal of Solid State Chemistry to be published, 43 pages, 16 figures

We present a detailed ${}^{7}$Li- and ${}^{31}$P-NMR study on single crystalline LiMnPO${}_{4}$ in the paramagnetic and antiferromagnetic phase (AFM, ${T}_{N}\ensuremath{\sim}34$ K). This allows us to determine the spin directions in the field-induced spin-flop phase. In addition, the anisotropic dipolar hyperfine coupling tensor of the ${}^{7}$Li and ${}^{31}$P nuclei is also fully determined by orientation and temperature-dependent NMR experiments and compared to the calculated values from crystal structure data. Deviations of the experimental values from the theoretical ones are discussed in terms of Mn disorder which is induced by Li disorder. In fact, the disorder in the Mn sublattice is directly revealed by diffuse x-ray scattering data. The present results provide experimental evidence for the Li diffusion strongly coupling to structural distortions within the MnPO${}_{4}$ host, which is expected to significantly affect the Li mobility as well as the performance of batteries based on this material.

The evolution of low-energy spin dynamics in the iron-based superconductor LaFeAsO$_{1-x}$F$_x$ was studied over a broad doping, temperature, and magnetic field range (x = 0 - 0.15, T up to 480K, H up to 30T) by means of As nuclear magnetic resonance (NMR). An enhanced spin-lattice relaxation rate divided by temperature, 1/T1T, in underdoped superconducting samples (x = 0.045, 0.05 and 0.075) suggests the presence of antiferromagnetic spin fluctuations, which are strongly reduced in optimally-doped (x = 0.10) and completely absent in overdoped (x = 0.15) samples. In contrast to previous analysis, Curie-Weiss fits are shown to be insufficient to describe the data over the whole temperature range. Instead, a BPP-type model is used to describe the occurrence of a peak in 1/T1T clearly above the superconducting transition, reflecting a progressive slowing down of the spin fluctuations down to the superconducting phase transition., Comment: 10 pages, 10 figures

LiMn 0.95 Ni 0.05 PO 4 single crystals have been grown for the first time by the travelling-solvent floating-zone method at low argon pressure. The grown sample exhibits large single crystalline grains as revealed by means of polarization microscopy, X-ray Laue back scattering, and single-crystal X-ray diffraction. The composition of the crystal was determined by Energy-dispersive X-ray (EDX) spectroscopy. LiMn 0.95 Ni 0.05 PO 4 orders in an orthorhombic olivine-like structure as expected and phase purity was confirmed by powder X-ray diffraction. An oriented cuboid with size of 2.4×2.5×2.7 mm 3 along a , b , and c crystalline directions, respectively, was used for anisotropic magnetic measurements.

authoren Orbital ordering has recently emerged as another important state in iron-based superconductors, and its role for superconductivity as well as its connection to magnetic order and orthorhombic lattice distortion are heavily debated. In order to search for signatures of this so-called nematic phase in oxypnictides, we revisit the normal state properties of the pnictide superconductor LaFeAsO1−x Fx with a focus on resistivity, Nernst effect, thermal expansion, and As nuclear magnetic resonance (NMR) data. The transport properties at the underdoped level exhibit pronounced anomalies at about the same temperature where undoped LaFeAsO develops long-range nematic ordering, i.e., at about 160 K. Furthermore, the As-NMR spin-lattice relaxation rate reveals a progressive slowing down of spin fluctuations. Yet, long-range magnetic order and also a detectable orthorhombic lattice distortion are absent. Thus, we conclude from the data that short-range orbital-nematic ordering or a slowly fluctuating form of it sets in near 160 K. Remarkably, all anomalies in the transport and also the indications of slow spin fluctuations disappear close to optimal doping which suggests that in LaFeAsO1−x Fx the nematic phase actually competes with superconductivity. Schematic electronic phase diagram of LaFeAsO1−x Fx.

We report a ${}^{63}$Cu NMR investigation in detwinned YBa${}_{2}$Cu${}_{3}$O${}_{y}$ single crystals, focusing on the highly underdoped regime ($y=6.35--6.6$). Measurements of both the spectra and the spin-lattice relaxation rates of ${}^{63}$Cu uncover the emergence of static order at a well-defined onset temperature ${T}_{0}$ with an as yet unknown order parameter. While ${T}_{0}$ is rapidly suppressed with increasing hole doping concentration $p$, the spin pseudogap was identified only near and above the doping content at which ${T}_{0}\ensuremath{\rightarrow}0$. Our data indicate the presence of a critical hole doping ${p}_{c}\ensuremath{\sim}0.1$, which may control both the static order at $pl{p}_{c}$ and the spin pseudogap at $pg{p}_{c}$.

We present high-field magnetization and Br-79 nuclear quadrupole resonance (NQR) and Te-125 nuclear magnetic resonance (NMR) studies in the weakly coupled Cu2+ (S = 1/2) tetrahedral system Cu2Te2O5Br2. The field-induced level crossing effects were observed by the magnetization measurements in a long-ranged magnetically ordered state which was confirmed by a strong divergence of the spin-lattice relaxation rate T-1(-1) at T-0 = 13.5 K. In the paramagnetic state, T-1(-1) reveals an effective singlet-triplet spin gap much larger than that observed by static bulk measurements. Our results imply that the inter-and the intratetrahedral interactions compete, but at the same time they cooperate strengthening effectively the local intratetrahedral exchange couplings. We discuss that the unusual feature originates from the frustrated intertetrahedral interactions.

$^{75}$As NMR investigation of a single crystal of superconducting LiFeAs is presented. The Knight shift and the \textit{in situ} ac susceptibility measurements as a function of temperature and external field are indicative of two superconducting (SC) transition temperatures, each of which is associated with its own upper critical field. Strikingly, the Knight shift maintains its normal state value over a temperature range in the SC state before it drops abruptly being consistent with spin-singlet pairing. Together with our previous NMR study, the anomalous SC state featured by the constant Knight shift is attributed to the extremely sensitive SC properties of LiFeAs, probably stemming from its proximity to a critical instability., The title and text were modified; accepted in J. Physics: Condensed matter

We report ${}^{139}$La and ${}^{63}$Cu nuclear magnetic and quadrupole resonance (NMR/NQR) studies in an underdoped La${}_{1.93}$Sr${}_{0.07}$CuO${}_{4}$ single crystal, focusing on the ${}^{139}$La NMR in the normal state. We demonstrate that the local structural distortions in the low-temperature orthorhombic structure cause the tilting of the direction of the electric field gradient (EFG) at the nuclei from the $c$ axis, resulting in two NMR central transition spectra at both the ${}^{139}$La and ${}^{63}$Cu nuclei in an external field. Taking into account the tilt angle of the EFG, the temperature dependence of the ${}^{139}$La spectra allowed us to determine the ${}^{139}$La Knight shift and the structural order parameter. The angle and temperature dependence of the ${}^{139}$La spectrum is in perfect agreement with the macroscopic average structure and proves a displacive transition. The ${}^{139}$La nuclear spin-lattice relaxation rates, ${T}_{1}^{\ensuremath{-}1}$, suggest that La${}_{1.93}$Sr${}_{0.07}$CuO${}_{4}$ undergoes a gradual change to a temperature-independent paramagnetic regime in the high-temperature region. Both the spectra and ${T}_{1}^{\ensuremath{-}1}$ of the ${}^{139}$La as a function of temperature reveal a sharp anomaly around ${T}_{S}=387(1)$ K, implying a first-order-like structural transition, and a dramatic change below $\ensuremath{\sim}70$ K arising from collective glassy spin freezing.

Magnetic correlations in superconducting LiFeAs were studied by elastic and by inelastic neutron-scattering experiments. There is no indication for static magnetic ordering, but inelastic correlations appear at the incommensurate wave vector ($0.5\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta},0.5\ensuremath{\mp}\ensuremath{\delta},0$) with $\ensuremath{\delta}\ensuremath{\sim}0.07$ slightly shifted from the commensurate ordering observed in other FeAs-based compounds. The incommensurate magnetic excitations respond to the opening of the superconducting gap by a transfer of spectral weight.