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The rising interest in increased manufacturing maturity of quantum processing units is pushing the development of alternative superconducting materials for semiconductor fab process technology. However, these are often facing CMOS process incompatibility. In contrast to common CMOS materials, such as Al, TiN, and TaN, reports on the superconductivity of other suitable transition-metal nitrides are scarce, despite potential superiority. Here, we demonstrate fully CMOS-compatible fabrication of HfN and ZrN thin films on state-of-the-art 300 mm semiconductor process equipment, utilizing reactive DC magnetron sputtering on silicon wafers. Measurement of mechanical stress and surface roughness of the thin films demonstrates process compatibility. We investigated the materials phase and stoichiometry by structural analysis. The HfN and ZrN samples exhibit superconducting phase transitions with critical temperatures up to 5.84 and 7.32 K, critical fields of 1.73 and 6.40 T, and coherence lengths of 14 and 7 nm, respectively. A decrease in the critical temperature with decreasing film thickness indicates mesoscopic behavior due to geometric and grain-size limitations. The results promise a scalable application of HfN and ZrN in quantum computing and related fields. [ABSTRACT FROM AUTHOR]

The multicaloric effect is described by a temperature or entropy change of a material triggered by external stimuli applied or removed simultaneously or sequentially. The prerequisite for this is a material exhibiting multiple ferroic states. However, direct measurements of the effect are rarely reported. Now, for this reason, we built a measurement device allowing to determine the adiabatic temperature change in pulsed magnetic fields and, simultaneously, under the influence of a uniaxial load. We selected the all- d -metal Heusler alloy Ni–Mn–Ti–Co for our first test because of its enhanced mechanical properties and enormous magneto- and elastocaloric effects. Ni–Mn–Ti–Co was exposed to pulsed magnetic fields up to 10 T and uniaxial stresses up to 80 MPa, and the corresponding adiabatic temperature changes were measured. With our new experimental tool, we are able to better understand multicaloric materials and determine their cross-coupling responses to different stimuli. [ABSTRACT FROM AUTHOR]

The performance of iron-based superconductors in high magnetic fields plays an important role for their practical application. In this work, we measured the magnetostriction and magnetization of BaFe1.908Ni0.092As2 single crystals using pulsed magnetic fields up to 60 T and static magnetic fields up to 33 T, respectively. A huge longitudinal magnetostriction (of the order of 10–4) was observed in the direction of twin boundaries. The magnetization measurements evidence a high critical-current density due to strong bulk pinning. By using magnetization data with an exponential flux-pinning model, we can reproduce the magnetostriction curves qualitatively. This result shows that the magnetostriction of BaFe1.908Ni0.092As2 can be well explained by a flux-pinning-induced mechanism. [ABSTRACT FROM AUTHOR]

We present an overview of selected copper-based quasi-2D square-lattice spin-1/2 materials with an easy-plane anisotropy, providing the possibility to study emergent Berezinskii-Kosterlitz-Thouless (BKT) correlations. In particular, in those materials with a comparatively small exchange coupling, the effective XY anisotropy of the low-temperature spin correlations can be controlled by an applied magnetic field, yielding a systematic evolution of the BKT correlations. In cases where the residual interlayer correlations are small enough, dynamical BKT correlations in the critical regime may be observed experimentally, whereas the completion of the genuine BKT transition is preempted by the onset of long-range order. [ABSTRACT FROM AUTHOR]

The observation of spinon excitations in the S = 1 2 triangular antiferromagnet Ca3ReO5Cl2 reveals a quasi-one-dimensional (1D) nature of magnetic correlations, in spite of the nominally 2D magnetic structure. This phenomenon is known as frustration-induced dimensional reduction. Here, we present high-field electron spin resonance spectroscopy and magnetization studies of Ca3ReO5Cl2, allowing us not only to refine spin-Hamiltonian parameters, but also to investigate peculiarities of its low-energy spin dynamics. We argue that the presence of the uniform Dzyaloshinskii-Moriya interaction (DMI) shifts the spinon continuum in momentum space and, as a result, opens a zero-field gap at the Γ point. We observed this gap directly. The shift is found to be consistent with the structural modulation in the ordered state, suggesting this material as a perfect model triangular-lattice system, where a pure DMI-spiral ground state can be realized. Frustration-induced dimensional reduction is manifested in lower dimensionality of magnetic correlations compared to that of the magnetic structure. Here the authors demonstrate the role of the uniform Dzyaloshinskii-Moriya interaction in the recently synthesized material Ca3ReO5Cl2 exhibiting dimensional reduction. [ABSTRACT FROM AUTHOR]

Magnetic fields are key ingredients for heating the solar corona to temperatures of several million Kelvin. A particularly important region with respect to this is the so-called magnetic canopy below the corona, where sound and Alfvén waves have roughly the same speed and can, therefore, easily transform into each other. We present the results of an Alfvén-wave experiment with liquid rubidium carried out in a pulsed field of up to 63T. At the critical point of 54T, where the speeds of Alfvén waves and sound coincide, a new 4 kHz signal appears in addition to the externally excited 8 kHz torsional wave. This emergence of an Alfvén wave with a doubled period is in agreement with the theoretical predictions of a parametric resonance between the two wave types. We also present preliminary results from numerical simulations of Alfvén and magneto-sonic waves using a compressible MHD code. [ABSTRACT FROM AUTHOR]

The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB6 is a subject of intense inquiry. Here we shed light on this question by accessing quantum oscillations in the high magnetic field-induced metallic regime above ≈47 T in YbB12, which we compare with the unconventional insulating regime. In the field-induced metallic regime, we find prominent quantum oscillations in the electrical resistivity characterised by multiple frequencies and heavy effective masses. The close similarity in Lifshitz-Kosevich low-temperature growth of quantum oscillation amplitude in insulating YbB12 to field-induced metallic YbB12, points to an origin of quantum oscillations in insulating YbB12 from in-gap neutral low energy excitations. Higher frequency Fermi surface sheets of heavy quasiparticle effective mass emerge in the field-induced metallic regime of YbB12 in addition to multiple heavy Fermi surface sheets observed in both insulating and metallic regimes. f-electron hybridisation is thus observed to persist from the unconventional insulating to the field-induced metallic regime of YbB12, in contrast to the unhybridised conduction electron Fermi surface observed in unconventional insulating SmB6. Our findings thus require an alternative model for YbB12, of neutral in-gap low energy excitations, wherein the f-electron hybridisation is retained. [ABSTRACT FROM AUTHOR]

We study the dependence of the magnetocaloric effect on the magnetic field-change-rate the first order magnetostructural transition in Mn3GaC by measuring the adiabatic temperature change ΔT at three different time scales: 11mTs-1, 700mTs-1, and ~1000T s-1. We find that the maximum adiabatic temperature-change of about 5K is reached in the 11mTs-1 and 700mTs-1 rates, whereas for the ~1000 T s-1-rate the transition lags the change in the magnetic field so that the maximum adiabatic temperature-change is not attained. [ABSTRACT FROM AUTHOR]

The present pulsed high-magnetic-field study on Ni50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields. [ABSTRACT FROM AUTHOR]

Most of solid-state spin physics arising from spin–orbit coupling, from fundamental phenomena to industrial applications, relies on symmetry-protected degeneracies. So does the Zeeman spin–orbit coupling, expected to manifest itself in a wide range of antiferromagnetic conductors. Yet, experimental proof of this phenomenon has been lacking. Here we demonstrate that the Néel state of the layered organic superconductor κ-(BETS)2FeBr4 shows no spin modulation of the Shubnikov–de Haas oscillations, contrary to its paramagnetic state. This is unambiguous evidence for the spin degeneracy of Landau levels, a direct manifestation of the Zeeman spin–orbit coupling. Likewise, we show that spin modulation is absent in electron-doped Nd1.85Ce0.15CuO4, which evidences the presence of Néel order in this cuprate superconductor even at optimal doping. Obtained on two very different materials, our results demonstrate the generic character of the Zeeman spin–orbit coupling. [ABSTRACT FROM AUTHOR]

High-Frequency and -Field EPR (HFEPR) studies of Fe(TPP)X (X = F, Cl, Br; I, TPP2−= meso-tetraphenylporphyrinate dianion) and far-IR magnetic spectroscopic (FIRMS) studies of Fe(TPP)Br and Fe(TPP)I have been conducted to probe magnetic intra- and inter-Kramers doublet transitions in these S = 5/2 metalloporphyrin complexes, yielding zero-field splitting (ZFS) and g parameters for the complexes: Fe(TPP)F, D = +4.67(1) cm−1, E = 0.00(1) cm−1, g⊥ = 1.97(1), g|| = 2.000(5) by HFEPR; Fe(TPP)Cl, D = +6.458(2) cm−1, E = +0.015(5) cm−1, E/D = 0.002, g⊥ = 2.004(3), g|| = 2.02(1) by HFEPR; Fe(TPP)Br, D = +9.03(5) cm−1, E = +0.047(5) cm−1, E/D = 0.005, giso = 1.99(1) by HFEPR and D = +9.05 cm−1, giso = 2.0 by FIRMS; Fe(TPP)I, D = +13.84 cm−1, E = +0.07 cm−1, E/D = 0.005, giso = 2.0 by HFEPR and D = +13.95 cm−1, giso = 2.0 by FIRMS (the sign of E was in each case arbitrarily assigned as that of D). These results demonstrate the complementary nature of field- and frequency-domain magnetic resonance experiments in extracting with high accuracy and precision spin Hamiltonian parameters of metal complexes with S > 1/2. The spin Hamiltonian parameters obtained from these experiments have been compared with those obtained from other physical methods such as magnetic susceptibility, magnetic Mössbauer spectroscopy, inelastic neutron scattering (INS), and variable-temperature and -field magnetic circular dichroism (VT-VH MCD) experiments. INS, Mössbauer and MCD give good agreement with the results of HFEPR/FIRMS; the others not as much. The electronic structure of Fe(TPP)X (X = F, Cl, Br, I) was studied earlier by multi-reference ab initio methods to explore the origin of the large and positive D-values, reproducing the trends of D from the experiments. In the current work, a simpler model based on Ligand Field Theory (LFT) is used to explain qualitatively the trend of increasing ZFS from X = F to Cl to Br and to I as the axial ligand. Tetragonally elongated high-spin d5 systems such as Fe(TPP)X exhibit D > 0, but X plays a key role. Spin delocalization onto X means that there is a spin–orbit coupling (SOC) contribution to D from X•, as opposed to none from closed-shell X−. Over the range X = F, Cl, Br, I, X• character increases as does the intrinsic SOC of X• so that D increases correspondingly over this range. [ABSTRACT FROM AUTHOR]

We present the first study of codoped iron-arsenide superconductors of the 122 family (Sr/Ba)1-x Kx Fe2-y Coy As2 with the purpose to increase the upper critical field Hc2 compared to single doped Sr/BaFe2 As2 materials. Hc2 was investigated by measuring the magnetoresistance in high pulsed magnetic fields up to 64 T. We find, that Hc2 extrapolated to T=0 is indeed enhanced significantly to ≈ 90 T for polycrystalline samples of Ba0.55 K0.45 Fe1.95 Co0.05 As2 compared to ≈75 T for Ba0.55 K0.45 Fe2 As2 and BaFe1.8 Co0.2 As2 single crystals. Codoping thus is a promising way for the systematic optimization of iron-arsenic based superconductors for magnetic-field and high-current applications. [ABSTRACT FROM AUTHOR]

A comprehensive characterization of the structural and magnetic properties of Fe-implanted rutile TiO2(110) is presented. Fe and FeTiO3 (ilmenite) nanocrystals (NCs) are identified by synchrotron-radiation x-ray diffraction. The majority of Fe NCs are crystallographically oriented with respect to the matrix following the relation Fe(001)[010]∥TiO2(110)[11_0]. Postannealing induced the out-diffusion of Fe and the growth of FeTiO3 at the cost of Fe NCs. Mössbauer spectroscopy and superconducting quantum interference device (SQUID) magnetometry reveal the corresponding evolution of magnetic properties, i.e., magnetization, and superparamagnetic blocking temperature. We unambiguously identify Fe NCs as the origin of the ferromagnetism. These Fe NCs possess a uniaxial in-plane magnetic anisotropy, such that the two Fe[100] axes are inequivalent. [ABSTRACT FROM AUTHOR]

Forty years after the discovery of the first organic superconductor, the nature of the superconducting state in these materials is still not fully understood. Here, I present an overview on the historical developments and current knowledge on this topic for the quasi-one- and quasi-two-dimensional (2D) organic charge-transfer salts. Thereby, I focus on the prototype materials based on the donor molecules tetramethyltetraselenafulvalene (TMTSF) and bisethylenedithio-tetrathiafulvalene (BEDT-TTF or ET for short). 2D organic superconductors based on the latter molecule are found to show Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states at high magnetic fields and low temperatures. Thermodynamic and nuclear magnetic resonance data give robust evidence for the existence of this FFLO state with modulated order parameter. [ABSTRACT FROM AUTHOR]

Viscosity measurements in combination with pulsed magnetic fields are developed by use of a quartz-crystal microbalance (QCM). When the QCM is immersed in liquid, the resonant frequency, f0, and the quality factor, Q, of the QCM change depending on (ρη)0.5, where ρ is the mass density and η the viscosity. During the magnetic-field pulse, f0 and Q of the QCM are simultaneously measured by a ringdown technique. The typical resolution of (ρη)0.5 is 0.5%. As a benchmark, the viscosity of liquid oxygen is measured up to 55 T. [ABSTRACT FROM AUTHOR]

We report the results of high-resolution neutron powder diffraction studies of FexO (x = 0.925, 0.94) in the vicinity of the low-temperature antiferromagnetic transition and at pressures up to 8 GPa. Our analysis shows that the P-T phase diagram of FexO is strongly affected by the composition and defect structure of the material. We observe the divergence of critical temperatures of magnetic and structural transitions. In contrast to the stoichiometric antiferromagnet MnO, we find no correlation between the magnitude of the magnetic moment of iron and the degree of the rhombohedral distortion in FexO. We suggest that the defect structure of antiferromagnetic FexO significantly influences the temperature of the structural transition. [ABSTRACT FROM AUTHOR]

The spin dynamics of the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4 is probed by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy. Temperature dependences of EPR parameters are studied in a broad temperature range between 1.4 and 200K for different orientations of the applied magnetic field. In the high-temperature regime (T⪢ J/kB), an unusually broad and anisotropic resonance line is detected, suggesting a sizeable Dzyaloshinskii-Moriya interaction. Employing the theory of exchange narrowing, the ratio of the Dzyaloshinskii-Moriya vector components, Dc/Da ≈ 0.3, is estimated. [ABSTRACT FROM AUTHOR]

We report results of magnetic and ultrasound studies of the sulfide spinel CoCr2S4, for which the multiferroicity has recently been suggested. Clear anomalies in the magnetic and acoustic properties have been observed at TN = 222K and in applied magnetic fields evidencing the important role of magnetoelastic interactions in this material. In contrast, no anomalies have been detected at TC = 28 K, where a spontaneous electric polarization and isostructural distortions have been reported. We have extracted the H-T phase diagram of CoCr2S4 from our experiments for magnetic fields applied along the h111i direction. We discuss our observations in relation to our earlier results obtained for the oxide multiferroic spinel CoCr2O4. [ABSTRACT FROM AUTHOR]

We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler alloy Ni50Mn35In15 by direct measurements in pulsed magnetic fields up to 6 and 20 T. The results in 6 T are compared with data obtained from heat-capacity experiments. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum adiabatic temperature change of δTad=-7K at 250K and a conventional field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field on a time scale of ~10 to 100ms, which is on the order of typical operation frequencies (10-100 Hz) of magnetocaloric cooling devices. Our results disclose that in shape-memory alloys, the different contributions to the MCE and hysteresis effects around the martensitic transition have to be carefully considered for future cooling applications. [ABSTRACT FROM AUTHOR]

We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler alloy Ni50Mn35In15 by direct measurements in pulsed magnetic fields up to 6 and 20 T. The results in 6 T are compared with data obtained from heat-capacity experiments. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum adiabatic temperature change of △Tad = --7 K at 250 K and a conventional field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field on a time scale of ~10 to 100 ms, which is on the order of typical operation frequencies (10-100 Hz) of magnetocaloric cooling devices. Our results disclose that in shape-memory alloys, the different contributions to the MCE and hysteresis effects around the martensitic transition have to be carefully considered for future cooling applications. [ABSTRACT FROM AUTHOR]

Ge films with a mean Ga content of about 8 and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change in the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters of up to 10 000 atoms. Since no percolating Ga clusters exist, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect. [ABSTRACT FROM AUTHOR]

Spin-lattice effects play an important role in many magnetic materials. In this short review, we give some examples of such effects studied in low-dimensional, frustrated as well as uranium-based antiferromagnets. Utilizing ultrasound measurements at low temperatures and high magnetic fields provides valuable information on the spin-strain interactions. Specifically phase transformations and critical phenomena in magnetic systems with strong spin-lattice interactions are fruitful grounds for sound-velocity and sound-attenuation measurements. [ABSTRACT FROM AUTHOR]

Si films sputter deposited on thermally oxidized Si are enriched with Ga by ion implantation through a SiO2 capping layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga-rich nanoinclusions are embedded in a nanocrystalline Si matrix. The metallic nanoinclusions become superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga-rich Si films show a wealth of low-temperature transport phenomena, which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance. The possibility to prepare and modify Ga-rich Si films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [ABSTRACT FROM AUTHOR]

In this short review, we report on the recently found growing experimental evidence for the existence of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in quasi-two-dimensional organic superconductors. At high magnetic fields aligned parallel to the conducting organic layers, we observe an upturn of the upper critical field beyond the Pauli limit, as evidenced by specific-heat and torque-magnetization measurements. Inside the superconducting state a second thermodynamic transition emerges. These features appear only in a very narrow angular region close to parallel-field orientation. [ABSTRACT FROM AUTHOR]

Results of systematic high-frequency electron spin resonance (ESR) studies of BaCrO, a weakly coupled $S=\frac{1}{2}$ dimer system, in magnetic fields up to 25 T are reported. Two pairs of ESR gapped modes corresponding to transitions from a spin-singlet ground state to the first excited triplet states with gaps, Δ=563 GHz and Δ=399 GHz, are revealed below H=12.5 T. The detection of the ground-state excitations by means of ESR clearly indicates the presence of a non-secular term allowing these transitions. A complex structure of the microwave absorption spectrum in magnetic fields above H is observed, those peculiarities are discussed. [ABSTRACT FROM AUTHOR]

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached. We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload. [ABSTRACT FROM AUTHOR]

Results of electron spin resonance studies of copper pyrimidine dinitrate (Cu-PM, [PM-Cu(NO)(HO)], PM = pyrimidine), a spin-1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interactions, in pulsed magnetic fields up to 63 T are reported. The field-induced gap shows a non-monotonic behavior with a minimum in the vicinity of the saturation field H=48.5 T. This is associated with a transition from the sine-Gordon region to a spin-polarized state with magnon excitations. By comparing the entire set of experimental data with results of density matrix renormalization group calculations for Cu-PM, the validity of the used theoretical approach is proven. [ABSTRACT FROM AUTHOR]

The magnetization of ErFeTi and HoFeTi single crystals was measured in pulsed magnetic fields up to 60 T. A number of field-induced phase transitions were observed. The inter-sublattice molecular fields were found to be 60 T in ErFeTi and 73 T in HoFeTi. [ABSTRACT FROM AUTHOR]

We present the temperature dependence of the specific heat of CoCrO between 2.08 K and 306 K in zero magnetic field. The lattice component can be described by the Komada-Westrum model with a characteristic temperature Θ = 541 K. The entropy of the magnetic component amounts to 33.51 J mol K at T = 298.15 K, in good agreement with the magnetic entropy of Co and Cr ions with completely quenched orbital moments. We compare our results with data available in literature. [ABSTRACT FROM AUTHOR]

We report on the design and successful testing (up to 55 T) of a 60 T long-pulse (LP) magnet with a pulse duration of 1500 ms at the Hochfeld-Magnetlabor Dresden. This magnet has the capability of producing magnetic fields with time and homogeneity characteristics suitable to host specific-heat and nuclear magnetic resonance (NMR) experiments. We describe the development of a specific-heat probe for this magnet, which uses the quasi-adiabatic heat-pulse method and enables magnetocaloric-effect measurements. Furthermore, we report the implementation of a NMR setup, consisting of home-built probe and spectrometer. Both experimental devices were tested successfully in the LP magnet up to 31 and 44 T, respectively. [ABSTRACT FROM AUTHOR]

We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77 K up to 91.4 T. Moreover, the magnetoresistance behavior at 290 K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges. [ABSTRACT FROM AUTHOR]

We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at. %. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channeling, secondary-ion-mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·1020 to 5.3·1020 cm-3 (0.4 to 1.2 at. %) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at. %. Higher concentrations lead to an increase of Tc from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m2 point to a large impact of the microstructure. [ABSTRACT FROM AUTHOR]

We report measurements of the temperature dependence of the radio frequency magnetic penetration depth in BaKFeAs and Ba(FeCo)As single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an H- T-phase diagram for the inter-plane ( H | c) and in-plane ( H | ab) directions for both compounds. For both field orientations in BaKFeAs we find a concave curvature of the H( T) lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe H( T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(FeCo)As. For this electron-doped compound, the data support a H( T) dependence that can be described by the Werthamer-Helfand-Hohenberg model for H | ab and a two-gap behavior for H | c. [ABSTRACT FROM AUTHOR]

Early work on the iron-arsenide compounds supported the view, that a reduced dimensionality might be a necessary prerequisite for high- T superconductivity. Later, however, it was found that the zero-temperature upper critical magnetic field, H(0), for the 122 iron pnictides is in fact rather isotropic. Here, we report measurements of the temperature dependence of the electrical resistivity, ρ( T), in BaKFeAs and BaKFeAs single crystals in zero magnetic field and in BaKFeAs in static and pulsed magnetic fields up to 60 T. We find that the resistivity of both compounds in zero field is well described by an exponential term due to inter-sheet umklapp electron-phonon scattering between light electrons around the M point to heavy hole sheets at the Γ point in reciprocal space. From our data, we construct an H- T phase diagram for the inter-plane ( H | c) and in-plane ( H | ab) directions for BaKFeAs. Contrary to published data for 122 underdoped FeAs compounds, we find that H( T) is in fact anisotropic in optimally doped samples down to low temperatures. The anisotropy parameter, γ = H/ H, is about 2.2 at T. For both field orientations we find a concave curvature of the H lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism, we perfectly can describe H and its anisotropy. [ABSTRACT FROM AUTHOR]

In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron-resonance studies under pulsed magnetic fields up to 60 T. [ABSTRACT FROM AUTHOR]

In this paper we consider various issues of design, fabrication, and performance of non-destructive pulsed magnets at the Dresden High Magnetic Field Laboratory. Currently, a variety of pulsed magnets are in operation in the laboratory. A 70 T/8.5 MJ magnet, having a 24 mm bore and generating field pulses of about 150 ms duration serves as a workhorse for external users and for in-house research. Smaller 60-65 T/1.5 MJ magnets with a bore of 20 mm and pulse duration of ~25 ms have been proven to be very reliable in operation. In addition, a new 90 T/9 MJ dual-coil magnet has recently achieved 87.2 T in a 20 mm bore. A 60 T/43 MJ long-pulse magnet is currently tested. Questions of magnet longevity, coil monitoring, as well as magnetic-field measurements are addressed. Further magnet-technology developments and the route to 100 T are discussed. [ABSTRACT FROM AUTHOR]

The transverse acoustic wave propagating along the [100] axis of the cubic paramagnet Tb3Ga5O12 (TGG) exhibits amplitude oscillations as a function of magnetic field applied in the direction of propagation. This magneto-acoustic Faraday effect shows a linear frequency dependence contrary to theoretical expectation which demands a quadratic frequency dependence. The c44 mode demonstrates also a strong softening of 6% up to 19 T, the magnetic field where an energy level of the CEF triplet branch starts to cross the quasi-doublet branch. This softening has the same origin, the magneto-elastic coupling, as the anomalies in the temperature dependence of the elastic constants and the magneto-acoustic Faraday effect. [ABSTRACT FROM AUTHOR]

We report on pulsed-field magnetization studies of the quasi-two-dimensional spin system [Cu(pyz)2(HF2)]PF6. The magnetization saturates at $B_{C}^{ab}=37.5$ T and $B_{C}^{c}=33.8$ T for in-plane and out-of-plane orientations of the applied magnetic field, respectively. In addition, the angular dependence of the g-factor studied by electron-spin resonance reveals orbital overlap in the ab plane suggesting a quasi-two-dimensional square-lattice network of Cu spins. It is argued that the high-field behavior is governed by the two-dimensional nature of the spin correlations due to the large anisotropy of the exchange couplings. [ABSTRACT FROM AUTHOR]

We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition. [ABSTRACT FROM AUTHOR]

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90×90 μm down to 20×20 μm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2–300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150×750 μm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors. [ABSTRACT FROM AUTHOR]

Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels. [ABSTRACT FROM AUTHOR]

We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice spin-1/2 antiferromagnet Cs2CuCl4 ( T N=0.6 K), in external magnetic fields up to 14 T, applied along the b axis, and at temperatures down to 300 mK. The results are analyzed with a quasi-two-dimensional hard-core boson theory based on exchange-striction coupling. There is a good qualitative agreement between theoretical and experimental results. [ABSTRACT FROM AUTHOR]

We report on measurements of the magnetization up to 7 T, of the specific heat and electrical resistivity in fields up to 14 T, and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh17S15. Our data allow us to complement the superconducting phase diagram. The existence of narrow 4 d-band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the moderately high electronic contribution to the specific heat of about 107 mJ/molK2, favoring the existence of a strong superconducting interaction. This fact, and the remarkably high upper critical field (exceeding the simple Pauli limit by a factor of two), give evidence of the uncommon nature of the superconductivity in Rh17S15. [ABSTRACT FROM AUTHOR]

We report resistivity and upper critical field B c2( T) data for As-deficient LaO0.9F0.1FeAs1− δ in a wide temperature and field range up to 60 T. These disordered samples exhibit a slightly enhanced superconducting transition at T c=29 K and a significantly enlarged slope d B c2/d T=−5.4 T/K near T c which contrasts with a flattening of B c2( T) starting near 23 K above 30 T. This flattening is interpreted as Pauli limiting behavior (PLB) with B c2(0)≈63 T. We compare our results with B c2( T)-data reported in the literature for clean and disordered samples. Whereas clean samples show no PLB for fields below 60 to 70 T, the hitherto unexplained flattening of B c2( T) for applied fields H ∥ ab observed for several disordered closely related systems is interpreted also as a manifestation of PLB. Consequences of our results are discussed in terms of disorder effects within the frame of conventional and unconventional superconductivity. [ABSTRACT FROM AUTHOR]