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Showing papers on "Relaxation (NMR) published in 2017"


Journal ArticleDOI
24 Aug 2017-Nature
TL;DR: Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations, indicating that magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
Abstract: Magnetic hysteresis is observed in a dysprosocenium complex at temperatures of up to 60 kelvin, the origin of which is the localized metal–ligand vibrational modes unique to dysprosocenium. The discovery of molecules that exhibit magnetic bistability raised hopes for the use of such molecular systems as tiny building blocks for magnetic data storage. Despite a quarter of a century of research, however, the temperatures at which these molecules display their desirable magnetic properties remain frustratingly low. Conrad Goodwin et al. report the synthesis and characterization of a molecular dysprosocenium complex that shows magnetic bistability up to 60 kelvin—tantalizingly close to liquid nitrogen temperatures, the point at which applications would start to become a realistic possibility. Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements include reading and manipulating single nuclear spins1,2, exploiting atomic clock transitions for robust qubits3 and, most recently, magnetic data storage in single atoms4,5. Single-molecule magnets exhibit magnetic hysteresis of molecular origin6—a magnetic memory effect and a prerequisite of data storage—and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets7, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin8,9,10 using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates11,12 (for example, 30 kelvin with 200 oersted per second)12. Here we report a hexa-tert-butyldysprosocenium complex—[Dy(Cpttt)2][B(C6F5)4], with Cpttt = {C5H2tBu3-1,2,4} and tBu = C(CH3)3—which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal–ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.

1,328 citations


Journal ArticleDOI
TL;DR: This review introduces the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification, and focuses discussion specifically on local order, free volume, irreversible chain adsorption, the Debye-Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature.
Abstract: When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at a constant rate, the structural relaxation time of the liquid eventually exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass - a solid lacking long-range order. Despite almost 100 years of research on the (liquid/)glass transition, it is not yet clear which molecular mechanisms are responsible for the unique slow-down in molecular dynamics. In this review, we first introduce the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification. We then analyse the impact of connectivity, structure, and chain environment on molecular motion at the length scale of a few monomers, as well as how macromolecular architecture affects the glass transition of non-linear polymers. We then discuss a revised picture of nanoconfinement, going beyond a simple picture based on interfacial interactions and surface/volume ratio. Analysis of a large body of experimental evidence, results from molecular simulations, and predictions from theory supports, instead, a more complex framework where other parameters are relevant. We focus discussion specifically on local order, free volume, irreversible chain adsorption, the Debye-Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature. We end by highlighting the molecular origin of distributions in relaxation times and glass transition temperatures which exceed, by far, the size of a chain. Fast relaxation modes, almost universally present at the free surface between polymer and air, are also remarked upon. These modes relax at rates far larger than those characteristic of glassy dynamics in bulk. We speculate on how these may be a signature of unique relaxation processes occurring in confined or heterogeneous polymeric systems.

306 citations


Journal ArticleDOI
TL;DR: It is shown that, in the presence of phonon dissipation, the relevant energy scale for the spin relaxation is given by the lower-lying phonon modes interacting with the local spins, which opens a channel for spin reversal at energies lower than that set by the magnetic anisotropy.
Abstract: The use of single molecule magnets in mainstream electronics requires their magnetic moment to be stable over long times. One can achieve such a goal by designing compounds with spin-reversal barriers exceeding room temperature, namely with large uniaxial anisotropies. Such strategy, however, has been defeated by several recent experiments demonstrating under-barrier relaxation at high temperature, a behaviour today unexplained. Here we propose spin-phonon coupling to be responsible for such anomaly. With a combination of electronic structure theory and master equations we show that, in the presence of phonon dissipation, the relevant energy scale for the spin relaxation is given by the lower-lying phonon modes interacting with the local spins. These open a channel for spin reversal at energies lower than that set by the magnetic anisotropy, producing fast under-barrier spin relaxation. Our findings rationalize a significant body of experimental work and suggest a possible strategy for engineering room temperature single molecule magnets.

301 citations


Journal ArticleDOI
TL;DR: A comprehensive review of the reported relaxation times in the literature in vivo at 3T for a large span of tissues is presented, and a detailed analysis of the different methods and sequences used to calculate the relaxation times is given.

172 citations


Journal ArticleDOI
TL;DR: A hydroxide-bridged five-coordinate dysprosium(iii) dimer with short Dy–O bonds was synthesized.
Abstract: A hydroxide-bridged centrosymmetric DyIII dimer with each DyIII being five-coordinated has been synthesized using bulky hindered phenolate ligands. Magnetic studies revealed that this compound exhibits a slow magnetic relaxation of a single-ion origin together with a step-like magnetic hysteresis of the magnetic coupled cluster. The thermal relaxation barrier of magnetization is 721 K in the absence of a static magnetic field, while the intramolecular magnetic interaction is very large among reported 4f-only dimers. CASSCF calculations with a larger active space were performed to understand the electronic structure of the compound. The thermal relaxation regime and the quantum tunneling regime are well separated, representing a good model to study the relaxation mechanism of SMMs with intramolecular Dy–Dy magnetic interactions.

151 citations


Journal ArticleDOI
TL;DR: In this article, the spin-phonon coupling leading to spin relaxation in the prototypical mononuclear single molecule magnet (tpaPh)Fe− was investigated and the nature of the most relevant vibrational modes giving rise to the relaxation was analyzed in detail.
Abstract: We perform a systematic investigation of the spin-phonon coupling leading to spin relaxation in the prototypical mononuclear single molecule magnet [(tpaPh)Fe]−. In particular we analyze in detail the nature of the most relevant vibrational modes giving rise to the relaxation. Our fully ab initio calculations, where the phonon modes are evaluated at the level of density functional theory and the spin-phonon coupling by mapping post-Hartree–Fock electronic structures onto an effective spin Hamiltonian, reveal that acoustic phonons are not active in the spin-phonon relaxation process of dilute SMMs crystals. Furthermore, we find that intra-molecular vibrational modes produce anisotropy tensor modulations orders of magnitude higher than those associated to rotations. In light of these results we are able to suggest new designing rules for spin-long-living SMMs which go beyond the tailoring of static molecular features but fully take into account dynamical features of the vibrational thermal bath evidencing those internal molecular distortions more relevant to the spin dynamics.

137 citations


Journal ArticleDOI
TL;DR: By theoretically identifying the most relevant vibrational modes, this methodology is able to offer general strategies to chemically design more resilient magnetic molecules, where the energy of the spin states is not coupled to vibrations.
Abstract: To design molecular spin qubits and nanomagnets operating at high temperatures, there is an urgent need to understand the relationship between vibrations and spin relaxation processes. Herein we develop a simple first-principles methodology to determine the modulation that vibrations exert on spin energy levels. This methodology is applied to [Cu(mnt)2]2– (mnt2– = 1,2-dicyanoethylene-1,2-dithiolate), a highly coherent complex. By theoretically identifying the most relevant vibrational modes, we are able to offer general strategies to chemically design more resilient magnetic molecules, where the energy of the spin states is not coupled to vibrations.

125 citations


Journal ArticleDOI
TL;DR: A record speed is measured for the phase transition of 26 fs into a long-lived excited state of the metal that persists out to >60 ps and the measured femtosecond timescale provides fundamental insight into the electronic speed limits of these complex phenomena.
Abstract: Coulomb correlations can manifest in exotic properties in solids, but how these properties can be accessed and ultimately manipulated in real time is not well understood. The insulator-to-metal phase transition in vanadium dioxide (VO2) is a canonical example of such correlations. Here, few-femtosecond extreme UV transient absorption spectroscopy (FXTAS) at the vanadium M2,3 edge is used to track the insulator-to-metal phase transition in VO2 This technique allows observation of the bulk material in real time, follows the photoexcitation process in both the insulating and metallic phases, probes the subsequent relaxation in the metallic phase, and measures the phase-transition dynamics in the insulating phase. An understanding of the VO2 absorption spectrum in the extreme UV is developed using atomic cluster model calculations, revealing V3+/d2 character of the vanadium center. We find that the insulator-to-metal phase transition occurs on a timescale of 26 ± 6 fs and leaves the system in a long-lived excited state of the metallic phase, driven by a change in orbital occupation. Potential interpretations based on electronic screening effects and lattice dynamics are discussed. A Mott-Hubbard-type mechanism is favored, as the observed timescales and d2 nature of the vanadium metal centers are inconsistent with a Peierls driving force. The findings provide a combined experimental and theoretical roadmap for using time-resolved extreme UV spectroscopy to investigate nonequilibrium dynamics in strongly correlated materials.

116 citations


Journal ArticleDOI
TL;DR: Thorough investigation of the DyIII congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of Ueff =51 cm-1 .
Abstract: Assembly of the triangular, organic radical-bridged complexes Cp*6Ln3(μ3-HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp*2Ln(BPh4) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three LnIII centers through the HAN3−. radical ligand. Thorough investigation of the DyIII congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of Ueff=51 cm−1. Magnetic coupling in the DyIII complex enables a large remnant magnetization at temperatures up to 3.0 K in the magnetic hysteresis measurements and hysteresis loops that are open at zero-field up to 3.5 K.

114 citations


Journal ArticleDOI
TL;DR: This work demonstrates that the evolution of behavior following a temperature quench is a primarily structural phenomenon: the structure changes considerably, but the relationship between structure and dynamics remains invariant, and shows that the relaxation time can be robustly computed from structure as quantified by softness.
Abstract: The dynamical glass transition is typically taken to be the temperature at which a glassy liquid is no longer able to equilibrate on experimental timescales. Consequently, the physical properties of these systems just above or below the dynamical glass transition, such as viscosity, can change by many orders of magnitude over long periods of time following external perturbation. During this progress toward equilibrium, glassy systems exhibit a history dependence that has complicated their study. In previous work, we bridged the gap between structure and dynamics in glassy liquids above their dynamical glass transition temperatures by introducing a scalar field called “softness,” a quantity obtained using machine-learning methods. Softness is designed to capture the hidden patterns in relative particle positions that correlate strongly with dynamical rearrangements of particle positions. Here we show that the out-of-equilibrium behavior of a model glass-forming system can be understood in terms of softness. To do this we first demonstrate that the evolution of behavior following a temperature quench is a primarily structural phenomenon: The structure changes considerably, but the relationship between structure and dynamics remains invariant. We then show that the relaxation time can be robustly computed from structure as quantified by softness, with the same relation holding both in equilibrium and as the system ages. Together, these results show that the history dependence of the relaxation time in glasses requires knowledge only of the softness in addition to the usual state variables.

112 citations


Journal ArticleDOI
TL;DR: This detailed experimental comparative study represents a fundamental step to understand the spin dynamics of potential molecular quantum bits, and enriches the guidelines to design molecule-based systems with enhanced quantum coherence.
Abstract: Here we report the investigation of the magnetization dynamics of a vanadyl complex with diethyldithiocarbamate (Et2dtc–) ligands, namely [VO(Et2dtc)2] (1), in both solid-state and frozen solution. This showed an anomalous and unprecedentedly observed field dependence of the relaxation time, which was modeled with three contributions to the relaxation mechanism. The temperature dependence of the weight of the two processes dominating at low fields was found to well correlate with the low energy vibrations as determined by THz spectroscopy. This detailed experimental comparative study represents a fundamental step to understand the spin dynamics of potential molecular quantum bits, and enriches the guidelines to design molecule-based systems with enhanced quantum coherence.

Journal ArticleDOI
TL;DR: In this article, an STM tip was employed to probe the spin dynamics and disentangle different effects leading to relaxation of single atoms on a surface, which can be useful in spintronics applications.
Abstract: Single atoms on a surface can be useful in spintronics applications, but their spin lifetime is limited by relaxation. By cleverly employing an STM tip, one can probe the spin dynamics and disentangle different effects leading to relaxation.

Journal ArticleDOI
TL;DR: It is found that double-quantum spin relaxation via electric field noise dominates T_{1} of near-surface NVs at low applied magnetic fields.
Abstract: We probe the relaxation dynamics of the full three-level spin system of near-surface nitrogen-vacancy (NV) centers in diamond to define a T_{1} relaxation time that sets the T_{2}≤2T_{1} coherence limit of the NV's subset qubit superpositions. We find that double-quantum spin relaxation via electric field noise dominates T_{1} of near-surface NVs at low applied magnetic fields. Furthermore, we differentiate 1/f^{α} spectra of electric and magnetic field noise using a novel noise-spectroscopy technique, with broad applications in probing surface-induced decoherence at material interfaces.

Journal ArticleDOI
TL;DR: A mononuclear hexacoordinate Cu(II) complex shows a field induced slow magnetic relaxation that is not facilitated by an energy barrier to spin reversal due to the zero-field splitting.
Abstract: A mononuclear hexacoordinate Cu(II) complex shows a field induced slow magnetic relaxation that is not facilitated by an energy barrier to spin reversal due to the zero-field splitting. Two relaxation channels were found: the magnetic field strongly supports the low-frequency relaxation path with a relaxation time as long as τ = 0.8 s at T = 1.9 K and B = 1.5 T. The mechanism of the relaxation at low temperature involves the dominant Raman process for this S = 1/2 spin system along with a temperature-independent term belonging to a quantum tunneling.

Journal ArticleDOI
TL;DR: The Dy-Sc nitride clusterfullerene Dy2ScN@C80-Ih exhibits slow relaxation of magnetization up to 76 K, and above 60 K, thermally-activated relaxation proceeds via the fifth-excited Kramers doublet with the energy of 1735 ± 21 K, which is the highest barrier ever reported for dinuclear lanthanide single molecule magnets.

Journal ArticleDOI
TL;DR: In this paper, the relationship between free volume distribution, chain motion, crystallinity, and the gas properties of PET upon strain-induced crystallization (SIC) at different stretch ratios was evaluated.
Abstract: The primary focus of this work was to evaluate the relationship between free volume distribution, chain motion, crystallinity, and the gas properties of PET upon strain-induced crystallization (SIC) at different stretch ratios. The formation of a three-phase structure containing rigid amorphous phase, mobile amorphous phase, and crystalline phase upon SIC was confirmed by differential scanning calorimetry and positron annihilation lifetime spectroscopy (PALS). Dynamic mechanical analysis and PALS indicated that there was a significant reduction in the fractional free volume upon orientation at an extension ratio of 3 × 3. Sub-Tg relaxation studies indicated that the activation energy of mechanical relaxation decreased with increasing the stretch ratio. Gas transport studies revealed that the reduction in permeability coefficient was mainly due to reduction in diffusivity. Permeation studies using gas molecules with different sizes revealed that strain-induced crystallization affects the free volume distri...

Journal ArticleDOI
TL;DR: In this article, the dielectric relaxation mechanism in the CuO pellet was studied by impedance spectroscopy, and the obtained impedance spectra indicated that the grain boundary effects and intergranular activities played a crucial role on the dieetics relaxation processes, which indicated that AC conduction mechanism could be well explained by the multihopping model at low frequencies, while high frequency AC conductivity data can be described by small polaron tuning model.

Journal ArticleDOI
TL;DR: A synthetic strategy to enhance the energy barrier in lanthanide-based SMMs by incorporating s- and d-block diamagnetic ions is proposed, which reduces quantum tunneling of magnetization effects, allowing for more desirable SMM characteristics.
Abstract: The synthesis and magnetic and theoretical studies of three isostructural heterometallic [CoIII2LnIII2(μ3-OH)2(o-tol)4(mdea)2(NO3)2] (Ln = Dy (1), Tb (2), Ho (3)) “butterfly” complexes are reported (o-tol = o-toluate, (mdea)2– = doubly deprotonated N-methyldiethanolamine). The CoIII ions are diamagnetic in these complexes. Analysis of the dc magnetic susceptibility measurements reveal antiferromagnetic exchange coupling between the two LnIII ions for all three complexes. ac magnetic susceptibility measurements reveal single-molecule magnet (SMM) behavior for complex 1, in the absence of an external magnetic field, with an anisotropy barrier Ueff of 81.2 cm–1, while complexes 2 and 3 exhibit field induced SMM behavior, with a Ueff value of 34.2 cm–1 for 2. The barrier height for 3 could not be quantified. To understand the experimental observations, we performed DFT and ab initio CASSCF+RASSI-SO calculations to probe the single-ion properties and the nature and magnitude of the LnIII–LnIII magnetic couplin...

Journal ArticleDOI
TL;DR: A momentum-resolved picture of the energy transfer from excited electrons to phonons is obtained and this constitutes a basis for monitoring and predicting out of equilibrium electrical and thermal transport properties for nanoscale applications of TMDCs.
Abstract: We investigate the interactions of photoexcited carriers with lattice vibrations in thin films of the layered transition metal dichalcogenide (TMDC) ${\mathrm{WSe}}_{2}$. Employing femtosecond electron diffraction with monocrystalline samples and first-principles density functional theory calculations, we obtain a momentum-resolved picture of the energy transfer from excited electrons to phonons. The measured momentum-dependent phonon population dynamics are compared to first-principles calculations of the phonon linewidth and can be rationalized in terms of electronic phase-space arguments. The relaxation of excited states in the conduction band is dominated by intervalley scattering between $\mathrm{\ensuremath{\Sigma}}$ valleys and the emission of zone boundary phonons. Transiently, the momentum-dependent electron-phonon coupling leads to a nonthermal phonon distribution, which, on longer time scales, relaxes to a thermal distribution via electron-phonon and phonon-phonon collisions. Our results constitute a basis for monitoring and predicting out of equilibrium electrical and thermal transport properties for nanoscale applications of TMDCs.

Journal ArticleDOI
TL;DR: SrIrO3 can effectively induce interfacial Dzyaloshinskii-Moriya interactions in superlattices, which would serve as a mechanism to develop spintronic devices with perovskite oxides, as well as explore rich emergent phenomena, including interfacial superconductivity and nontrivial topological surface states.
Abstract: The heterostructure interface provides a powerful platform for exploring rich emergent phenomena, such as interfacial superconductivity and nontrivial topological surface states. Here, SrRuO3/SrIrO3 superlattices were epitaxially synthesized. The magnetic and magneto-transport properties of these superlattices were characterized. A broad cusp-type splitting in the zero-field-cooling/field-cooling temperature-dependent magnetization and magnetization relaxation, which follows the modified stretched function model, accompanied by double hysteresis magnetization loops were demonstrated. These physical effects were modulated by the SrIrO3 layer thickness, which confirms the coexistence of interfacial spin glass and ferromagnetic ordering in the superlattices. In addition, the topological Hall effect was observed at low temperatures, and it is weakened with the increase of the SrIrO3 layer thickness. These results suggest that a noncoplanar spin texture is generated at the SrRuO3/SrIrO3 interfaces because of t...

Journal ArticleDOI
TL;DR: In this paper, a model of two-dimensional deformations for two-temperature theory at the free surface under the excitation of thermoelastic wave by pulsed laser for a semi-infinite semiconducting medium is studied.
Abstract: A novel model of two-dimensional deformations for two-temperature theory at the free surface under the excitation of thermoelastic wave by pulsed laser for a semi-infinite semiconducting medium is studied. The effect of mechanical force during a photothermal process is investigated. The mathematical methods of the Lord–Shulman (LS includes one relaxation time) and Green–Lindsay (GL with two relaxation times) theories as well as the classical dynamical coupled theory (CD) are used. An exact expression for displacement components, force stresses, carrier density and distribution of temperature are obtained using the harmonic wave analysis. Combinations of two-temperature and photothermal theories are obtained analytically. Comparisons of the results are made between the three theories also. The effects of thermoelectric coupling parameter, two-temperature parameter on the displacement component, force stress, carrier density, and distribution of temperature for silicon (Si) medium have been illustrated graphically. The variations of the considered variables with the horizontal distance have been discussed.

Journal Article
TL;DR: By employing time-dependent density functional theory calculations, this work systematically study the size-dependent electronic, optical absorption, and emission properties of black phosphorus quantum dots (BPQDs).
Abstract: Understanding electron transitions in black phosphorus nanostructures plays a crucial role in applications in electronics and optoelectronics. In this work, by employing time-dependent density functional theory calculations, we systematically study the size-dependent electronic, optical absorption, and emission properties of black phosphorus quantum dots (BPQDs). Both the electronic gap and the absorption gap follow an inversely proportional law to the diameter of BPQDs in conformity to the quantum confinement effect. In contrast, the emission gap exhibits anomalous size dependence in the range of 0.8–1.8 nm, which is blue-shifted with the increase of size. The anomaly in fact arises from the structure distortion induced by the excited-state relaxation, and it leads to a huge Stokes shift in small BPQDs.

Journal ArticleDOI
TL;DR: Experimental techniques in the laboratory for nuclear magnetic resonance (NMR) in zero and ultralow magnetic field (below 0.1 μT) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free 87Rb atomic magnetometer are reviewed.
Abstract: We review instrumentation for nuclear magnetic resonance (NMR) in zero and ultra-low magnetic field (ZULF, below 0.1 $\mu$T) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free (SERF) $^{87}$Rb atomic magnetometer. The typical sensitivity is 20-30 fT/Hz$^{1/2}$ for signal frequencies below 1 kHz and NMR linewidths range from Hz all the way down to tens of mHz. These features enable precision measurements of chemically informative nuclear spin-spin couplings as well as nuclear spin precession in ultra-low magnetic fields.

Journal ArticleDOI
TL;DR: In this article, the Dzyaloshinskii-Moriya interaction in the cubic chiral magnet MnSi stabilizes a magnetic helix -a periodic one-dimensional modulation of the magnetization.
Abstract: The Dzyaloshinskii-Moriya interaction in the cubic chiral magnet MnSi stabilizes a magnetic helix - a periodic one-dimensional modulation of the magnetization. The orientation of this helix is determined by weak magnetocrystalline anisotropies, but it can be reoriented by applying a magnetic field. Here, the authors have studied this reorientation process by means of small-angle neutron scattering and susceptibility measurements. Their results are in excellent agreement with predictions of an effective mean-field theory taking into account the precise symmetries of the crystal structure. Measurements of the magnetization and ac susceptibility provide evidence that the reorientation of helimagnetic domains is associated with large relaxation times exceeding seconds. In addition, hysteresis at the Ising transitions indicates, within the same theoretical framework, the formation of an abundance of plastic deformations of the helical spin order. These deformations comprise topologically nontrivial disclinations, reminiscent of the skyrmions discovered recently in the same class of materials.

Journal ArticleDOI
TL;DR: This work uses the NV intrinsic nuclear spin as a nonvolatile classical memory to store NMR information, while suppressing sensor back-action on the target using controlled decoupling of sensor, memory, and target.
Abstract: In nanoscale metrology, dissipation of the sensor limits its performance. Strong dissipation has a negative impact on sensitivity, and sensor–target interaction even causes relaxation or dephasing of the latter. The weak dissipation of nitrogen-vacancy (NV) sensors in room temperature diamond enables detection of individual target nuclear spins, yet limits the spectral resolution of nuclear magnetic resonance (NMR) spectroscopy to several hundred Hertz, which typically prevents molecular recognition. Here, we use the NV intrinsic nuclear spin as a nonvolatile classical memory to store NMR information, while suppressing sensor back-action on the target using controlled decoupling of sensor, memory, and target. We demonstrate memory lifetimes up to 4 min and apply measurement and decoupling protocols, which exploit such memories efficiently. Our universal NV-based sensor device records single-spin NMR spectra with 13 Hz resolution at room temperature. Dissipation of the sensor is a limiting factor in metrology. Here, Pfender et al. suppress this effect employing the nuclear spin of an NV centre for robust intermediate storage of classical NMR information, allowing then to record single-spin NMR spectra with 13 Hz resolution at room temperature.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated a series of telechelic polyisobutylenes, previously shown to exhibit self-healing, by means of small-angle X-ray scattering and rheology.
Abstract: We investigated a series of telechelic polyisobutylenes, previously shown to exhibit self-healing, by means of small-angle X-ray scattering and rheology. All samples form a dense, dynamic network of interconnected micelles resulting from aggregation of the functional groups and leading to viscoelastic behavior. The dynamic character of this network manifests itself in the appearance of terminal flow at long time scales. While the elastic properties are distinctly molecular weight dependent, the terminal relaxation time is controlled by the functional end groups. The yielding properties under large deformation during startup shear experiments can be understood by a model of stress activation of the dynamic bonds. Stress relaxation experiments help to separate the nonlinear response into two contributions: a fast collapse of the network and a slow relaxation, happening on the time scale of the terminal relaxation. The latter is also known to control self-healing of the collapsed structure.

BookDOI
21 Dec 2017
TL;DR: The theory of NUCLEAR MAGNETIZATION is discussed in this article, where the authors describe the properties of the Nucleus of an atom and its properties in a magnetic field.
Abstract: THE THEORY OF NUCLEAR MAGNETIZATION The Properties of the Nucleus of an Atom The Nucleus in a Magnetic Field The Source of the NMR Signal A Basic NMR Spetrometer Questions THE MAGNETIC FIELD AT THE NUCLEUS: NUCLEAR SCREENING THE CHEMICAL SHIFT Effects Due to the Molecule Isotope Effects Effects Due to Unpaired Electrons The Chemical Shift Note on Sample Preparation, Standardization, and Solvent and Temperature Effects Questions INTERNUCLEAR SPIN-SPIN COUPLING The Mutual Effects of Nuclear Magnets on Resonance Positions The Appearance of Multiplets Arising form Spin-Spin Coupling Spin-Spin Coupling Satellites The Description of Spin Systems Second-Order Effects Questions NUCLEAR MAGNETIC RELAXATION Relaxation Processes in Assemblies of Nuclear Spins Dipole-Dipole Relaxation Quardrupolar Relaxation Spin Rotation Relaxation: Detailed Molecular Motion Chemical Shift Anisotropy Relaxation Scalar Relaxation Examples of 13C Relaxation Times Questions THE SPECTROMETER The Magnet and Field Homogeneity The Probe Field-Frequency Lock The Transmitter The Detection System Production of the Spectrum Rapid Multiple Pulsing Manipulations of Collected Data Questions MAKING THE SPINS DANCE Decoupling Composite Pulses Refocusing Pulse Questions NMR SPECTRA OF EXCHANGING AND REACTING SYSTEMS Systems at Equilibrium Reaction Monitoring of Systems not at Equilibrium Questions MULTIPLE RESONANCE AND ONE-DIMENSIONAL PULSE SEQUENCES Decoupling Difference Spectroscopy The Nuclear Overhauser Effect One-Dimensional Mutliphase Sequences Exercises in Spectral Interpretation TWO-DIMENSIONAL NMR SPECTROSCOPY J-Resolved Two-Dimensional NMR Spectroscopy Homonuclear COSY NMR Spectroscopy Heteronuclear COSY NMR Spectroscopy HOHAHA or TOCSY Two-Dimensional INADEQUATE Overhauser and Magnetization Transfer Based Two-Dimensional NMR Spectroscopy Inverse Detection Three-Dimensional NMR Spectroscopy Questions MAGNETIC RESONANCE IMAGING AND BIOMEDICAL NMR Producing an Image Whole Body Imaging Diffusion and Flow Chemical Shift Imaging Biological Uses of Imaging - Imaging Microscopy Industrial Uses of Imaging Techniques Biomedical NMR HIGH-RESOLUTION SOLID-STATE NMR Magic Angle Spinning Spin-1/2 Nuclei with Low Magnetogyric Ratios I=1/2 Nuclei with High Magnetogyric Ratios MAS of Quadropolar Nuclei Some Applications Deuterium, An Integral-Spin Nucleus Questions Bibliography Answers to Questions Index

Journal ArticleDOI
TL;DR: The results suggest that magnetic relaxation is a significant and unsolved barrier to achieving the high spatial resolutions predicted by the Langevin model for large core size SPIOs.
Abstract: Magnetic particle imaging (MPI) is a promising new tracer modality with zero attenuation in tissue, high contrast and sensitivity, and an excellent safety profile. However, the spatial resolution of MPI is currently around 1 mm in small animal scanners. Especially considering tradeoffs when scaling up MPI scanning systems to human size, this resolution needs to be improved for clinical applications such as angiography and brain perfusion. One method to improve spatial resolution is to increase the magnetic core size of the superparamagnetic nanoparticle tracers. The Langevin model of superparamagnetism predicts a cubic improvement of spatial resolution with magnetic core diameter. However, prior work has shown that the finite temporal response, or magnetic relaxation, of the tracer increases with magnetic core diameter and eventually leads to blurring in the MPI image. Here we perform the first wide ranging study of 5 core sizes between 18 and 32 nm with experimental quantification of the spatial resolution of each. Our results show that increasing magnetic relaxation with core size eventually opposes the expected Langevin behavior, causing spatial resolution to stop improving after 25 nm. Different MPI excitation strategies were experimentally investigated to mitigate the effect of magnetic relaxation. The results show that magnetic relaxation could not be fully mitigated for the larger core sizes and the cubic resolution improvement predicted by the Langevin was not achieved. This suggests that magnetic relaxation is a significant and unsolved barrier to achieving the high spatial resolutions predicted by the Langevin model for large core size superparamagnetic iron oxides.

Journal ArticleDOI
TL;DR: In this paper, the spin precession of an electron in the valley is sharply coupled with the lowest-lying optical phonon that release the in-plane mirror symmetry, which indicates that spin randomization of MoS 2 is mainly caused by spin-phonon interaction.
Abstract: The valley degree of freedom and the possibility of spin-valley coupling of solid materials have attracted growing interest, and the relaxation dynamics of spin- and valley-polarized states has become an important focus of recent studies. In spin-orbit-coupled inversion-asymmetric two-dimensional materials, such as MoS_{2} it has been found that the spin randomization is characteristically faster than the time scales for inter- and intra-valley scatterings. In this study, we examined the ultrafast non-collinear spin dynamics of an electron valley in monolayer MoS_{2} by using real-time propagation time-dependent density functional theory. We found that the spin precession of an electron in the valley is sharply coupled with the lowest-lying optical phonon that release the in-plane mirror symmetry. This indicates that the spin randomization of MoS_{2} is mainly caused by spin-phonon interaction. We further suggest that flipping of spins in a spin-orbit-coupled system can be achieved by the control over phonons.

Journal ArticleDOI
TL;DR: Working with two benzoate derivatives with different numbers of non-coordinated fluoro-substituents, single crystal structure analysis demonstrates that the metal cations in the two resulting compounds are connected by the alternating triple-bridge of μ-1,1-azido, syn,syn-carboxylate and μ2-methanol, contributing to analogously linear Cu(ii) chain-like motifs with slightly different intrachain and interchain geometric parameters.
Abstract: Employing two benzoate derivatives with different numbers of non-coordinated fluoro-substituents, 2-fluorobenzoic acid (2-Hfba) and 2,6-difluorobenzoic acid (2,6-Hdfba), two new azido-copper coordination polymers, [Cu(2-fba)(N3)(CH3OH)]n (1) and [Cu(2,6-dfba)(N3)(CH3OH)]n (2), have been successfully isolated, and then structurally and magnetically investigated. Single crystal structure analysis demonstrates that the metal cations in the two resulting compounds are connected by the alternating triple-bridge of μ-1,1-azido, syn,syn-carboxylate and μ2-methanol, contributing to analogously linear 1D Cu(II) chain-like motifs with slightly different intrachain and interchain geometric parameters. The fine-tuned structures lead to variant magnetic properties in the two title compounds. Although a dominant ferromagnetic coupling between adjacent Cu(II) ions within each chain due to the counter-complementarity of the multiple superexchange pathways is observed in both compounds, the interesting plots of magnetic ordering and slow magnetic relaxation, which are rare in most of the reported azido-Cu(II) architectures, only occur in compound 1, while 2 behaves as an antiferromagnet consisting of ferromagnetic Cu(II) chains. The heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in 1 and the typical behavior of antiferromagnets in 2. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on both compounds to obtain the qualitatively theoretical interpretation of the magnetic behaviors.