Showing papers by "Alois Loidl published in 2015"
TL;DR: A new Néel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices is found in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy.
Abstract: Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Neel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.
569 citations
TL;DR: This study studies the interplay between magnetism and electric polarization in the lacunar spinel GaV4S8, which undergoes a structural transition associated with orbital ordering at 44 K and reveals a complex magnetic phase diagram below 13 K, including ferromagnetic, cycloidal, and Néel-type skyrmion lattice (SkL) phases.
Abstract: Skyrmions are whirl-like topological spin objects with high potential for future magnetic data storage. A fundamental question that is relevant to both basic research and application is whether ferroelectric (FE) polarization can be associated with skyrmions' magnetic texture and whether these objects can be manipulated by electric fields. We study the interplay between magnetism and electric polarization in the lacunar spinel GaV4S8, which undergoes a structural transition associated with orbital ordering at 44 K and reveals a complex magnetic phase diagram below 13 K, including ferromagnetic, cycloidal, and Neel-type skyrmion lattice (SkL) phases. We found that the orbitally ordered phase of GaV4S8 is FE with a sizable polarization of ~1 μC/cm(2). Moreover, we observed spin-driven excess polarizations in all magnetic phases; hence, GaV4S8 hosts three different multiferroic phases with coexisting polar and magnetic order. These include the SkL phase, where we predict a strong spatial modulation of FE polarization close to the skyrmion cores. By taking into account the crystal symmetry and spin patterns of the magnetically ordered phases, we identify exchange striction as the main microscopic mechanism behind the spin-driven FE polarization in each multiferroic phase. Because GaV4S8 is unique among known SkL host materials owing to its polar crystal structure and the observed strong magnetoelectric effect, this study is an important step toward the nondissipative electric field control of skyrmions.
144 citations
TL;DR: It is shown that the relaxational process causing the excess wing can also be detected by neutron scattering, which directly couples to density fluctuations.
Abstract: The relaxational dynamics in glass-forming glycerol and glycerol mixed with LiCl is investigated using different neutron scattering techniques. The performed neutron spin echo experiments, which extend up to relatively long relaxation time scales of the order of 10ns, should allow for the detection of contributions from the so-called excess wing. This phenomenon, whose microscopic origin is controversially discussed, arises in a variety of glass formers and, until now, was almost exclusively investigated by dielectric spectroscopy and light scattering. Here we show that the relaxational process causing the excess wing can also be detected by neutron scattering, which directly couples to density fluctuations.
132 citations
TL;DR: It is shown that the conductivity of ILs depends in a systematic way not only on their glass temperature but also on the so-called fragility, characterizing the non-canonical super-Arrhenius temperature dependence of their ionic mobility.
Abstract: Ionic liquids (ILs) are salts that are liquid close to room temperature. Their possible applications are numerous, e.g., as solvents for green chemistry, in various electrochemical devices, and even for such "exotic" purposes as spinning-liquid mirrors for lunar telescopes. Here we concentrate on their use for new advancements in energy-storage and -conversion devices: Batteries, supercapacitors or fuel cells using ILs as electrolytes could be important building blocks for the sustainable energy supply of tomorrow. Interestingly, ILs show glassy freezing and the universal, but until now only poorly understood dynamic properties of glassy matter, dominate many of their physical properties. We show that the conductivity of ILs, an essential figure of merit for any electrochemical application, depends in a systematic way not only on their glass temperature but also on the so-called fragility, characterizing the non-canonical super-Arrhenius temperature dependence of their ionic mobility.
98 citations
TL;DR: In this article, the conductivity of ionic liquids (ILs) is investigated in terms of their non-canonical super-Arrhenius temperature dependence of their ionic mobility.
Abstract: Ionic liquids (ILs) are salts that are liquid close to room temperature. Their possible applications are numerous, e.g., as solvents for green chemistry in various electrochemical devices, and even for such "exotic" purposes as spinning-liquid mirrors for lunar telescopes. Here we concentrate on their use for new advancements in energy-storage and -conversion devices: Batteries, supercapacitors or fuel cells using ILs as electrolytes could be important building blocks for the sustainable energy supply of tomorrow. Interestingly, ILs show glassy freezing and the universal, but until now only poorly understood dynamic properties of glassy matter, dominate many of their physical properties. We show that the conductivity of ILs, an essential figure of merit for any electrochemical application, depends in a systematic way not only on their glass temperature but also on the so-called fragility, characterizing the non-canonical super-Arrhenius temperature dependence of their ionic mobility.
71 citations
TL;DR: In this article, the authors investigated the system SrCo2V2O8, a realization of the weakly-coupled Ising-like XXZ antiferromagnetic chains, by terahertz spectroscopy with and without applied magnetic field.
Abstract: For quasi-one dimensional quantum spin systems theory predicts the occurrence of a confinement of spinon excitation due to interchain couplings. Here we investigate the system SrCo2V2O8, a realization of the weakly-coupled Ising-like XXZ antiferromagnetic chains, by terahertz spectroscopy with and without applied magnetic field. At low temperatures a series of excitations is observed, which split in a Zeeman-like fashion in an applied magnetic field. These magnetic excitations are identified as the theoretically predicted spinon-pair excitations. Using a one dimensional Schrodinger equation with a linear confinement potential imposed by weak interchain couplings, the hierarchy of the confined spinons can be fully described.
56 citations
Posted Content•
TL;DR: In this paper, the authors reported the discovery of a Skyrmion lattice in the polar magnetic semiconductor GaV$_4$S$_8$ with rhombohedral symmetry and easy axis anisotropy.
Abstract: Following the early prediction of the skyrmion lattice (SkL) - a periodic array of spin vortices - it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with C$_{nv}$ symmetry were identifed as ideal SkL hosts in pioneering theoretical studies this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV$_4$S$_8$ with rhombohedral (C$_{3v}$) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic feld but instead confned to the magnetic easy axis. Supporting theory attributes these unique features to a new non-chiral or Neel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.
54 citations
Journal Article•
TL;DR: Spin-polarized scanning tunneling microscopy reveals the magnetic ordering of a strongly correlated material and reveals that the magnetic order in the monoclinic phase is a unidirectional stripe order; in the orthorhombic phase at higher excess iron concentration, a transition to a phase with coexisting magnetic orders in both directions is observed.
52 citations
TL;DR: By combining THz and MHz-GHz spectroscopy techniques, the relaxational dynamics arising from coupled orbital and polar fluctuations in this material are detected and its temperature dependence in the paraelectric as well as in the ferroelectric phase is traced.
Abstract: We present a dielectric spectroscopy study of the polar dynamics linked to the orbitally driven ferroelectric transition in the Skyrmion host GaV(4)S(8). By combining THz and MHz-GHz spectroscopy techniques, we succeed in detecting the relaxational dynamics arising from coupled orbital and polar fluctuations in this material and trace its temperature dependence in the paraelectric as well as in the ferroelectric phase. The relaxation time significantly increases when approaching the critical temperature from both sides of the transition. It is natural to assume that these polar fluctuations map the orbital dynamics at the Jahn-Teller transition. Because of the first-order character of the orbital-ordering transition, the relaxation time shows an enormous jump of about 5 orders of magnitude at the polar and structural phase transition.
42 citations
TL;DR: Evidence for nematic electronic states in the iron-chalcogenide superconductor FeSe0.4Te0.6 from quasi-particle scattering detected in spectroscopic maps is provided and the relation to superconductivity and the influence on the coherence length are discussed.
Abstract: The emergence of nematic electronic states accompanied by a structural phase transition is a recurring theme in many correlated electron materials, including the high-temperature copper oxide- and iron-based superconductors. We provide evidence for nematic electronic states in the iron-chalcogenide superconductor FeSe0.4Te0.6 from quasi-particle scattering detected in spectroscopic maps. The symmetry-breaking states persist above T c into the normal state. We interpret the scattering patterns by comparison with quasi-particle interference patterns obtained from a tight-binding model, accounting for orbital ordering. The relation to superconductivity and the influence on the coherence length are discussed.
41 citations
TL;DR: In this article, the authors provide an overview of the dielectric properties of a variety of organic charge transfer salts, based on both, data reported in literature and their own experimental results.
Abstract: This topical review provides an overview of the dielectric properties of a variety of organic charge-transfer salts, based on both, data reported in literature and our own experimental results. Moreover, we discuss in detail the different processes that can contribute to the dielectric response of these materials. We concentrate on the family of the 1D (TMTTF)2 X systems and the 2D BEDT-TTF-based charge-transfer salts, which in recent years have attracted considerable interest due to their often intriguing dielectric properties. We will mainly focus on the occurrence of electronic ferroelectricity in these systems, which also includes examples of multiferroicity.
TL;DR: This work provides a thorough investigation of magnetoelectric coupling, polarization and dielectric constants of the ordered magnetic and polar phases of single-crystalline Cu2OSeO3 in external magnetic fields up to 150 mT and at temperatures below 60 K.
Abstract: Insulating helimagnetic Cu2OSeO3 shows sizeable magnetoelectric effects in its skyrmion phase. Using magnetization measurements, magneto-current analysis and dielectric spectroscopy, we provide a thorough investigation of magnetoelectric coupling, polarization and dielectric constants of the ordered magnetic and polar phases of single-crystalline Cu2OSeO3 in external magnetic fields up to 150 mT and at temperatures below 60 K. From these measurements we construct a detailed phase diagram. Especially, the skyrmion phase and the metamagnetic transition of helical to conical spin order are characterized in detail. Finally we address the question if there is any signature of polar order that can be switched by an external electric field, which would imply multiferroic behaviour of Cu2OSeO3.
TL;DR: A linear correlation of the magnetic-field-induced change of the dielectric constant and the Magnetic-field dependent magnetization is observed, consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K.
Abstract: We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr2S4 in external magnetic fields. The ferrimagnetic ordering temperatures TC ≈ 170 K and the transition at TOO ≈ 10 K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the state below TOO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60 K. Below TOO this contraction is followed by a moderate expansion of the sample for fields larger than ~4.5 T. The transition at TOO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < TOO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K.
TL;DR: The glassy dynamics of plastic-crystalline cyclo-octanol and ortho-carborane, where only the molecular reorientational degrees of freedom freeze without long-range order, is investigated by nonlinear dielectric spectroscopy and shows marked differences to canonical glass formers.
Abstract: The glassy dynamics of plastic-crystalline cyclo-octanol and ortho-carborane, where only the molecular reorientational degrees of freedom freeze without long-range order, is investigated by nonlinear dielectric spectroscopy Marked differences to canonical glass formers show up: While molecular cooperativity governs the glassy freezing, it leads to a much weaker slowing down of molecular dynamics than in supercooled liquids Moreover, the observed nonlinear effects cannot be explained with the same heterogeneity scenario recently applied to canonical glass formers This supports ideas that molecular relaxation in plastic crystals may be intrinsically nonexponential Finally, no nonlinear effects were detected for the secondary processes in cyclo-octanol
TL;DR: It is shown that the conductivity of Li(+) ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones.
Abstract: Finding new ionic conductors that enable significant advancements in the development of energy-storage devices is a challenging goal of current material science. Aside of material classes as ionic liquids or amorphous ion conductors, the so-called plastic crystals (PCs) have been shown to be good candidates combining high conductivity and favorable mechanical properties. PCs are formed by molecules whose orientational degrees of freedom still fluctuate despite the material exhibits a well-defined crystalline lattice. In the present work, we show that the conductivity of Li+ ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones. Dielectric spectroscopy reveals that this is accompanied by a stronger coupling of ionic and reorientational motions. These findings, which can be understood in terms of an optimized “revolving door” mechanism, open a new path towards the development of better solid-state electrolytes.
TL;DR: In this article, a detailed investigation of the out-of-plane electrical properties of charge-ordered multiferroic charge-transfer salts has been carried out, and the existence of polar and non-polar stacks of the organic molecules in this material, preventing long-range ferroelectricity has been suggested.
Abstract: A detailed investigation of the out-of-plane electrical properties of charge-ordered $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{I}}_{3}$ provides clear evidence for ferroelectricity. Similar to multiferroic $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}[\mathrm{N}(\mathrm{CN})}_{2}]\mathrm{Cl}$, the polar order in this material is ascribed to the occurrence of bond- and site-centered charge order. Dielectric response typical for relaxor ferroelectricity is found deep in the charge-ordered state. We suggest an explanation in terms of the existence of polar and nonpolar stacks of the organic molecules in this material, preventing long-range ferroelectricity. The results are discussed in relation to the formation or absence of electronic polar order in related charge-transfer salts.
TL;DR: In this article, the authors examined the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field and showed that singlet-triplet excitations are typically not allowed in pure spin systems, demonstrating the entangled spin and orbital character of singlet ground and triplet excited states.
Abstract: Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate the characteristic length of the singlet correlations to be ξ/(a/2)≈8.2 (where a/2 is the nearest neighbor lattice constant), which establishes FeSc2S4 as a SOL with long-range entanglement.
TL;DR: The biocompatibility based on a low cytotoxicity in the non-neutron-activated state in combination with the hydrophilic nature of the tungsten oxide shell makes the coated magnetic FePt nanoparticles ideal candidates for advanced radiopharmaceutical applications.
TL;DR: In this paper, the authors show that the conductivity of Li+ ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones.
Abstract: Finding new ionic conductors that enable significant advancements in the development of energy-storage devices is a challenging goal of current material science. Aside of material classes as ionic liquids or amorphous ion conductors, the so-called plastic crystals (PCs) have been shown to be good candidates combining high conductivity and favourable mechanical properties. PCs are formed by molecules whose orientational degrees of freedom still fluctuate despite the material exhibits a well-defined crystalline lattice. Here we show that the conductivity of Li+ ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones. Dielectric spectroscopy reveals that this is accompanied by a stronger coupling of ionic and reorientational motions. These findings, which can be understood in terms of an optimised "revolving door" mechanism, open a new path towards the development of better solid-state electrolytes.
TL;DR: In this article, nonlinear dielectric measurements of glass-forming 1-propanol, a prototypical example for the monohydroxy alcohols that are known to exhibit unusual relaxation dynamics, namely an additional Debye relaxation, slower than the structural α relaxation.
Abstract: We present nonlinear dielectric measurements of glass-forming 1-propanol, a prototypical example for the monohydroxy alcohols that are known to exhibit unusual relaxation dynamics, namely an additional Debye relaxation, slower than the structural α relaxation. Applying high ac fields of 468 kV/cm allows for a detailed investigation of the nonlinear properties of all three relaxation processes occurring in 1-propanol, namely the Debye, α , and β relaxation. Both the field-induced variations of dielectric constant and loss are reported. Polarization saturation and the absorption of field energy govern the findings in the Debye-relaxation regime, well consistent with the suggested cluster-like nature of the relaxing entities. The behavior of the α relaxation is in good accord with the expectations for a heterogeneous relaxation scenario. Finally, the Johari–Goldstein β -relaxation in 1-propanol seems to exhibit no or only weak field dependence, in agreement with recent findings for the excess wing of canonical glass formers.
TL;DR: In this article, the authors examined the use of metal-organic framework (MOF) systems as host materials for the investigation of glassy dynamics in confined geometry and found different degrees of deviations from bulk behavior depending on pore size, demonstrating that MOFs are well suited host systems for confinement investigations.
Abstract: In this work, we examine the use of metal-organic framework (MOF) systems as host materials for the investigation of glassy dynamics in confined geometry. We investigate the confinement of the molecular glass former glycerol in three MFU-type MOFs with different pore sizes (MFU stands for “Metal-Organic Framework Ulm-University”) and study the dynamics of the confined liquid via dielectric spectroscopy. In accord with previous reports on confined glass formers, we find different degrees of deviations from bulk behavior depending on pore size, demonstrating that MOFs are well-suited host systems for confinement investigations.
TL;DR: This work investigates the confinement of the molecular glass former glycerol in three MFU-type MOFs with different pore sizes and study the dynamics of the confined liquid via dielectric spectroscopy.
Abstract: In this work we examine the use of metal-organic framework (MOF) systems as host materials for the investigation of glassy dynamics in confined geometry. We investigate the confinement of the molecular glass former glycerol in three MFU-type MOFs with different pore sizes and study the dynamics of the confined liquid via dielectric spectroscopy. In accord with previous reports on confined glass formers, we find different degrees of deviations from bulk behavior depending on pore size, demonstrating that MOFs are well-suited host systems for confinement investigations.
TL;DR: In this article, the authors used terahertz and far-infrared spectroscopy to study low-lying excitations in a spin-orbiton, an excitation of strongly entangled spins and orbitals.
Abstract: In ${\mathrm{FeSc}}_{2}{\mathrm{S}}_{4}$ spin-orbital exchange competes with strong spin-orbit coupling, suppressing long-range spin and orbital order and, hence, this material represents one of the rare examples of a spin-orbital liquid ground state. Moreover, it is close to a quantum-critical point separating the ordered and disordered regimes. Using terahertz and far-infrared spectroscopy we study low-lying excitations in ${\mathrm{FeSc}}_{2}{\mathrm{S}}_{4}$ and provide clear evidence for a spin-orbiton, an excitation of strongly entangled spins and orbitals. It becomes particularly well pronounced upon cooling, when advancing deep into the quantum-critical regime. Moreover, indications of an underlying structureless excitation continuum are found, a possible signature of quantum criticality.
Journal Article•
TL;DR: The magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field are examined to demonstrate the entangled spin and orbital character of singlet ground and triplet excited states.
Abstract: Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate the characteristic length of the singlet correlations to be ξ/(a/2)≈8.2 (where a/2 is the nearest neighbor lattice constant), which establishes FeSc2S4 as a SOL with long-range entanglement.
TL;DR: Both the valence shift and the shapes of the absorption edges suggest a change from localized to itinerant character of the Cu electronic states with increasing x, while the Ru electrons remain localized.
Abstract: In the solid-solution series LayCu3RuxTi4−xO12+δ (0 ≤ x ≤ 4) the Cu and Ru electronic states are highly correlated. With increasing Ru content x the system properties change from a paramagnetic insulator with colossal dielectric constant to a heavy-fermion metal. To further elucidate the occurring phase transitions, the valences of Cu and Ru have been investigated utilizing XANES measurements at the Cu-K and the Ru-K absorption edges. It was found that the Ru oxidation number is close to +4 in all samples, while the Cu valence linearly decreases from +2 for the titanate (x = 0) to +1.6 for the ruthenate (x = 4). Additional thermogravimetric measurements have been used to determine the oxygen content and rather high oxygen excesses up to δ ≈ 0.7 (for x = 0.5) were obtained. The additional oxygen for x < 2 is required to compensate the constant Ru +4 valence. Our findings are in accordance with the reported phase transitions of the magnetic and transport properties. Both the valence shift and the shapes of the absorption edges suggest a change from localized to itinerant character of the Cu electronic states with increasing x, while the Ru electrons remain localized. Analogous results concerning the valences were found for the PryCu3RuxTi4−xO12+δ and NdyCu3RuxTi4−xO12+δ solid-solution series.
TL;DR: In this paper, a new magnetic phase transition was observed in the frustrated antiferromagnet, which renormalizes the velocity and amplitude of the transverse acoustic mode, whereas the longitudinal mode is not affected.
Abstract: A new magnetic phase transition, which we assign to the separation of two different spiral phases, has been observed by ultrasound studies below the N\'eel temperature (${T}_{N}=7.8$ K) in the frustrated antiferromagnet ${\mathrm{CdCr}}_{2}{\mathrm{O}}_{4}$. This transition renormalizes the velocity and amplitude of the transverse acoustic mode ${c}_{T}$ whereas the longitudinal mode ${c}_{L}$ is not affected. The specific heat does not show any significant change in the entropy at this transition. Furthermore, in an applied magnetic field, the mode ${c}_{T}$ exhibits extended metastable magnetostructural states neighboring the one-half magnetization plateau in ${\mathrm{CdCr}}_{2}{\mathrm{O}}_{4}$. By applying an exchange-striction model we can quantitatively describe the field dependence of the sound velocity below and above the one-half magnetization plateau.
TL;DR: In this article, the effect of Cu doping on nuclear, magnetic, and dielectric properties was investigated by combining different techniques, viz, heat capacity and magnetization measurements, which showed that with increasing Cu concentration magnetic frustration decreases, leading to the stabilization of commensurate magnetic ordering.
Abstract: We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{WO}}_{4}$ for $0\ensuremath{\le}x\ensuremath{\le}0.19$ by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gr\"uneisen approximation. Dielectric measurements show a low temperature phase transition below about 9--10 K. Furthermore, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.
TL;DR: The obtained results prove the bimodality of the hydration shell dynamics of lysozyme solutions and find indications of a fragile-to-strong transition of hydration water.
Abstract: We present the frequency- and temperature-dependent dielectric properties of lysozyme solutions in a broad concentration regime, measured at subzero temperatures, and compare the results with measurements above the freezing point of water and on hydrated lysozyme powder. Our experiments allow examining the dynamics of unfreezable hydration water in a broad temperature range. The obtained results prove the bimodality of the hydration shell dynamics. In addition, we find indications of a fragile-to-strong transition of hydration water.