Measurement of spin-lattice relaxation times with longitudinal detection

New experimental schemes to measure spin-lattice relaxation times T1 on the basis of inversion-recovery and saturation-recovery experiments with longitudinal detection are introduced. With this approach, paramagnetic species with T1 values as short as 20 ns can be measured. Possibilities to reduce unwanted signals and instrumental artifacts are analyzed. An experiment where the signal is induced directly by the time-dependent M2 magnetization is also proposed. Experimental results for organic radicals and defect centers are presented and compared with data obtained with conventional techniques, and a metal complex at 250 K is analyzed where it is very difficult to get information about relaxation times with established methods because of fast spin-spin relaxatio

The dynamics of magnetic ordering in a natural hemo-ilmenite solid solution

We investigated the micromagnetic properties of hemo-ilmenite particles in an alluvial soil. All magnetic accessory minerals except the weathering resistant hemo-ilmenite grains were removed from the soil matrix by chemical treatment with concentrated acid followed by magnetic separation. X-ray diffraction revealed hemo-ilmenite grains with single crystal properties and an ilmenite mole fraction of y = 0.86. Magnetization versus applied magnetic field plots in a temperature range between 6 and 300 K were recorded in order to study the hysteresis and the exchange properties. In addition, field and frequency-dependent AC susceptibility measurements were performed with and without a DC bias field in order to analyse the dynamic magnetization of the sample down to 3 K. The hemo-ilmenite particles are considered as a mixed system with nano-sized cation-ordered areas (COA) and cation-disordered areas (CDA), which differ in their local Fe(III) concentration. Ferrimagnetic single-domain order in the Fe(III)-enriched CDA started at about 220 K. Upon cooling gradual transdomain transformation generates multidomain order. A maximum in the blocking distribution was reached at 44 K, followed by the onset of spin-glass dynamics. At lower temperature, blocking of superparamagnetic clusters in the COA created antiferromagnetic (AFM) ordering, which became more prominent with decreasing temperature. The interaction between the spin-glass like CDA and the AFM areas was documented by the onset of exchange bias at T < 20 K. The occurrence of exchange bias as well as spin-glass dynamics in the hemo-ilmenite grains is probably an effect of the inhomogeneity of the local Fe(III) concentration. This effect leaves a magnetically competitive regime with areas showing ilmenite-like magnetic properties, and Fe(III) rich disordered areas with magnetic long-range ordering up to 220 K and frustration near the ordering temperature of ilmenit

Hyperpolarized xenon nuclear spins detected by optical atomic magnetometry

We report the use of an atomic magnetometer based on nonlinear magneto-optical rotation with frequency modulated light (FM NMOR) to detect nuclear magnetization of xenon gas. The magnetization of a spin-exchange-polarized xenon sample ($1.7$cm$^3$ at a pressure of $5$bar, natural isotopic abundance, polarization 1%), prepared remotely to the detection apparatus, is measured with an atomic sensor (which is insensitive to the leading field of 0.45 G applied to the sample; an independent bias field at the sensor is $140 \mu$G). An average magnetic field of $\sim 10$nG induced by the xenon sample on the 10-cm diameter atomic sensor is detected with signal-to-noise ratio $\sim 10$, limited by residual noise in the magnetic environment. The possibility of using modern atomic magnetometers as detectors of nuclear magnetic resonance and in magnetic resonance imaging is discussed. Atomic magnetometers appear to be ideally suited for emerging low-field and remote-detection magnetic resonance applications.Comment: 4 pages, 4 figure

Electron spin coherence near room temperature in magnetic quantum dots

We report on an example of confined magnetic ions with long spin coherence near room temperature. This was achieved by confining single Mn2+ spins in colloidal semiconductor quantum dots (QDs) and by dispersing the QDs in a proton-spin free matrix. The controlled suppression of Mn–Mn interactions and minimization of Mn–nuclear spin dipolar interactions result in unprecedentedly long phase memory (TM ~ 8 μs) and spin–lattice relaxation (T1 ~ 10 ms) time constants for Mn2+ ions at T = 4.5 K, and in electron spin coherence observable near room temperature (TM ~ 1 μs)

Insights on Water Interaction at the Interface of Nitrogen Functionalized Hydrothermal Carbons

Hydrothermal carbon (HTC) derived from biomass is a class of cost-efficient, eco-friendly functional carbon materials with various potential applications. In this work, solid-state nuclear magnetic resonance (NMR), longitudinal (T1) relaxation time and diffusion NMR were employed to investigate the structure and water dynamics for HTC and nitrogen-functionalized hydrothermal carbon (N-HTC) samples ((N)-HTC). Results showed that the presence of N-functional groups influences the water interaction with (N)-HTC more strongly than surface area, pore size distribution or oxygenated functional groups. Furthermore, the degree of water interaction can be tuned by adjusting the synthesis temperature and the precursor ratio. Water motion was more strongly inhibited in N-HTC than in N-free HTC, thereby suggesting the existence of a differently structured hydration shell around N-HTC particles. In addition, the diffusion data of water in the N-HTC material shows two components that do not exchange on the time scale of the experiment (tens of milliseconds), indicating a significant fraction of slow mobile water that exists inside the structure of N-HTC. 1H–2H isotope exchange and cross-polarization NMR results show this internal water only in a near-surface layer of the N-HTC particles. Based on these findings, a model for water interaction with (N)-HTC particles is proposed

Polysiloxane-Based Single-Ion Conducting Polymer Blend Electrolyte Comprising Small-Molecule Organic Carbonates for High-Energy and High-Power Lithium-Metal Batteries

Single-ion conducting polymer electrolytes are considered particularly attractive for realizing high-performance solid-state lithium-metal batteries. Herein, a polysiloxane-based single-ion conductor (PSiO) is investigated. The synthesis is performed via a simple thiol-ene reaction, yielding flexible and self-standing polymer electrolyte membranes (PSiOM) when blended with poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). When incorporating 57 wt% of organic carbonates, these polymer membranes provide a Li$^{+}$ conductivity of >0.4 mS cm$^{-1}$ at 20 °C and a wide electrochemical stability window of more than 4.8 V. This excellent electrochemical stability allows for the highly reversible cycling of symmetric Li||Li cells as well as high-energy Li||LiNi$_{0.6}$Mn$_{0.2}$Co$_{0.2}$O$_{2}$2 (NMC$_{622}$) and Li||LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_{2}$ (NMC$_{811}$) cells for several hundred cycles at relatively high discharge and charge rates. Remarkably, Li||NMC$_{811}$ cells with high mass loading cathodes provide more than 76% capacity retention at a high current density of 1.44 mA cm$^{-2}$, thus rendering this polymer electrolyte suitable for high-performance battery applications

Experimental evidence for the relaxation coupling of all longitudinal 7Li magnetization orders in the superionic conductor Li10GeP2S12

This contribution addresses the experimental proof of the relaxation coupling of the 7Li (I = 3/2) longitudinal magnetization orders in the solid-state electrolyte Li10GeP2S12 (LGPS). This effect was theoretically described by Korb and Petit in 1988 but has not yet been shown experimentally. In a 2D-T1/spin-alignment echo (SAE) experiment, the inverse Laplace transformation of the spectral component over two time dimensions revealed the asymmetric course of the spin-lattice relaxation following from the coupling of all longitudinal orders. These observations were supported by Multi-quantum-filter experiments and by simulations of the 2D-T1/SAE experiment with a lithium spin system. Since the asymmetric relaxation effects are directly dependent on the velocities and degrees of freedom of ion motion they could be used especially in fast Li-ion conductors as a separation tool for environments with different mobility processes

Critical assessment of the evidence for striped nanoparticles

There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evidence for the presence of stripes). Through a combination of an exhaustive re-analysis of the original data, in addition to new experimental measurements of a simple control sample comprising entirely unfunctionalised particles, we show that all of the STM evidence for striped nanoparticles published to date can instead be explained by a combination of well-known instrumental artefacts, or by issues with data acquisition/analysis protocols. We also critically re-examine the evidence for the presence of ligand stripes which has been claimed to have been found from transmission electron microscopy, nuclear magnetic resonance spectroscopy, small angle neutron scattering experiments, and computer simulations. Although these data can indeed be interpreted in terms of stripe formation, we show that the reported results can alternatively be explained as arising from a combination of instrumental artefacts and inadequate data analysis techniques