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1.
Selective single and double quantum excitation pulsed NMRON has been utilized to obtain rotation patterns, free induction decays, and spin echoes in antiferromagnetic54Mn−MnCl2·4H2O and the quasi-2 dimensional ferromagnet54Mn−Mn(COOCH3)2·4H2O. The pulsed technique is well suited to observing fast spin-lattice relaxation and T1 values down to 100 ms have been measured in these systems. These short times may make magnetic insulators viable hosts for on-line experiments. The dependence on field and temperature of the54Mn spin-lattice relaxation time T1 has been investigated and a T1 minimum at high fields observed in both systems. A spin-spin relaxation time T2≈50 μs is measured in54Mn−MnCl2·4H2O. The observation of NMRON in the paramagnetic phase of MnCl2·4H2O allows the resonant frequencies in the antiferromagnetic and paramagnetic phases to be compared, yielding a value for the zero point spin deviation in the former phase.  相似文献   

2.
The mechanism of nuclear spin-lattice relaxation in insulating magnetically ordered crystals at low temperatures is discussed. In 3-dimensional systems the relaxation time T1 is long, but in the lower dimensional systems it can be quite short making them possible candidates for hosts in on-line experiments. An experiment in 2-dimensional54Mn−Mn (COOCH3)2·4H2O is discussed with particular reference to the relatively short value of T1 in low applied fields. A preliminary experiment in the 1-dimensional system54Mn−(CH3)4NMnCl3 (TMMC) is also described. Pulsed NMRON measurements in54Mn−MnCl2·4H2O are outlined and the advant-systems with fast relaxation emphasized.  相似文献   

3.
54Mn NMRON in the mixed halide antiferromagnet, Mn(Br X Cl1−X )2 · 4H2O, for varying external field, is reported. Significant qualitative differences are found between these NMRON transitions and those of the two terminal compounds, especially in respect to line widths. A tentative assignment is made to most of the observed NMRON transitions out to 0.8 T. An unidentified lower frequency inhomogeneous signal, present only at the lowest temperatures, with no counterpart in the terminal compounds, is also reported.  相似文献   

4.
Pulsed NMRON, CW NMRON and thermal NMR-NO methods have been utilized to study54Mn-MnCl2 · 4H2O. The54Mn spin-lattice relaxation timeT 1 in zero applied field has been measured between 35 and 90 mK in the antiferromagnetic phase. Above 65 mK the dominant relaxation mechanism is a Raman process with the electronic magnons, but at lower temperatures a direct process takes over. NMRON has been observed for the first time in the paramagnetic phase, and a line width of 300 kHz, with both homogeneous and inhomogeneous contributions, is observed. In the antiferromagnetic phase the line width is 35 kHz, and there are also homogeneous and inhomogeneous contributions. The dependence ofT 1 for the54Mn spins on field and temperature was studied in the paramagnetic phase. AT 1 minimum centred atB 0=2.64 T was observed. The hyperfine parameter <54 AS>/h=−513.6(3) MHz in the paramagnetic phase, and comparison with the value in the antiferromagnetic phase gives 0.013(1) for the zero point spin deviation.  相似文献   

5.
Benam  M. R.  Pond  J.  Goehring  L.  Kotlicki  A.  Turrell  B. G. 《Hyperfine Interactions》2001,136(3-8):415-419
Although the effects of impurities in metallic magnets have been extensively studied there have been far fewer experiments on impurities in insulating magnets, and, in an effort to understand this problem, we have investigated the effect of impurities in various systems. In MnCl2⋅4H2O samples doped with 1.6, 4.0 and 6.2% Co, the 54Mn NMRON line is significantly broadened compared to the line in the pure crystal and shows structure on the low frequency side. The nuclear spin-lattice relaxation time is also lower by an order of magnitude. 54Mn has also been doped into FeCl2⋅4H2O for which a 4-sublattice structure has been proposed and some details of this structure have been obtained. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

6.
Pulsed and continuous wave NMRON, and NMR thermally detected by Nuclear Orientation have been used to investigate the magnetic properties of the quasi-2-dimensional ferromagnet 54Mn-Mn(COOCH3)·4H2O. The NMR frequencies of both the 54Mn spins and the abundant 55Mn spins have been determined for the two crystalline lattice sites Mn1 and Mn2. The line widths of the 54Mn resonances are homogeneously broadened to about 300 kHz, and the 55Mn resonances are significantly pulled down in frequency. The spin-lattice relaxation times in low applied magnetic fields are short with T1 for the Mn2 site being much less than the value for the Mn1 site. Level crossing is observed between the Mn1 and Mn2 resonances in an applied field of 2.6 T. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

7.
Recently, pulsed NMRON experiments have been carried out on trace amounts of radioactive54Mn in the antiferromagnet MnCl24H2O at 500 MHz (Le Gros et al. [1]). In this compound, the quadrupole splitting between the two lowest NMR transitions is ≈3 MHz, which precludes the use of non-selective (hard) rf pulses. Yet within the restricted 2*2 manifold, associated with a given transition, the nuclear rotation is “hard”. In this paper, the theory of “selective-hard” NMRON and MQ-NMR experiments is developed within the framework of irreducible tensor operators. In essence, the theory extends the early work of Jaynes [4] to deal with the higher-order multipolar states created during the course of a given NMR experiment. Several new pulsed NMRON and MQ-NMR experiments are proposed. For example, it is demonstrated how “ouble resonance”, “selective-hard” experiments on the pseudo spin-1 manifold spanned by |±1> and |0> Zeeman states of any integer spinI could be used to extract small chemical shifts in the face of very large quadrupole splittings.  相似文献   

8.
The measurements of the rotational spectrum of 1,4-dioxane-water complex, performed by pulsed jet Fourier transform microwave spectroscopy, have been extended to the 7–18.5 GHz frequency region and to two additional isotopologues, 1,4-dioxane···H2 17O and 1,4-dioxane···HOD. The effective orientation of water in the complex has been obtained from the 17O quadrupole coupling constants.  相似文献   

9.
A practical method of nuclear spin cooling in the mK region, based on dramatic reduction in the spin-lattice relaxation time T1 at the antiferromagnetic-spin flop and spin flopparamagnetic phase transitions, is described. Far lower temperatures (down to 13 mK) than have been obtained to date (~ 90 mK) are achieved in reasonable times, greatly increasing the sensitivity of NMRON. Following resonance, active isotope spins can be rapidly reset (in times ~ 1 second) to thermal equilibrium. For54Mn in MnCl2.4H2O, hyperfine parameters A=?203.75 MHz, P=0.155 MHz and the exchange/ crystal field parameter combination Bex + 4¦D¦/gμB=1.355 T have been determined from good agreement between perturbation theory to second order and detailed NMRON results in applied fields parallel to the easy axis in the range 0-0.7 T. Splitting of observed lines in zero applied field (? 3.05 MHz) is mainly due to the pseudo-quadrupole (second order magnetic) interaction. Small third order effects (~0.05 MHz) have been resolved.  相似文献   

10.
The effect on the most intense M=3→2 NMRON line of54MnMnCl2. 4H2O resulting from a magnetic field B0 applied along the crystalline c- and b-axes is observed. Possible mechanisms for these results are discussed.  相似文献   

11.
Two tetrahydrate manganese salts, MnBr2·4H2O and Mn(COOCH3)2·4H2O have been studied by nuclear orientation. Two54Mn NMRON lines were observed in the bromide at 499.75(4) MHz and 501.6 (1) MHz allowing hyperfine parameters to be estimated. The spin-flop transition was also observed in this salt. Although considerable -ray anisotropy was observed in the acetate no resonances have yet been observed.  相似文献   

12.
Infrared reflection spectra of single crystals of BeSO4·4H2O and BeSO4·4D2O have been obtained in polarized light at 300°K and at 14°K in the region between 4000 cm?1 and 300 cm?1. By a Kronig-Kramers analysis, the frequencies of the infrared active transitions have been calculated. These transitions are attributed to internal vibrations of the water molecules and sulfate ions and, in the region between 1000 cm?1 and 300 cm?1, especially to internal and external vibrations of the tetrahedral Be++·4aqu-complexes. The vibrational modes of these complexes consist of a superposition of translational and librational modes of the water molecules and translational modes of the central Be++-ion. The vibrational frequencies and normal modes of this complex have been calculated in a central-force model, and force-constants have been determined by fitting the calculated frequencies to the observed spectra. The calculations have shown that the modes, which comprise mainly translational motions of the water molecules, are strongly coupled with librational motions of the water molecules. On the other hand, there exist pure librational modes with practically no admixture of translational motions. The optimum sets of force constants for the BeSO4·4H2O crystal and the BeSO4·4D2O crystal differ in a manner which can be understood under the assumption that the dimensions of the Be(D2O)4 complex are about 0.1 Å larger than those of the Be(H2O)4 complex. Some arguments supporting this conclusion will be discussed.  相似文献   

13.
The absorption spectra of CeCl3·7 H2O, LaCl3·7 H2O, CeCl3·7 D2O and LaCl3·7 D2O have been measured at low temperatures in the region of the 4 f→4 f infrared transitions. The energy levels of the Ce3+-ion in these compounds have been derived. The infrared phonon transitions have also been determined from the reflection spectra of these crystals measured in the region between 4000 cm?1 and 50 cm?1. Some of the energy levels of the Ce3+-ions in the deuterated crystals are shifted for about 10 wavenumbers against those in CeCl3·7 H2O. These shifts are probably due to an interaction of the electronic levels with resonant phonon-states in one or the other of the two compounds.  相似文献   

14.
A comparative analysis has been carried out on the Raman spectra of FeSO4·nH2O (n = 1, 4, 7) including the 2D‐analogs. The effects of changing the degrees of hydration have been found from the lattice, SO42− internal, and H2O internal modes. Increasing degrees of hydration shift the intense ν1(SO4) peak to lower wavenumbers and reduce the amount of splitting on the ν3(SO4) peaks. Some of the water librational bands cause the broadening of the ν4(SO4) peaks in FeSO4·7H2O and the ν2(SO4) peaks in FeSO4·7D2O. The ν2(H2O) band in FeSO4·H2O is red‐shifted in excess of 100 cm−1 relative to the unperturbed H2O band. Between 240 and 190 K and between 140 and 90 K in the spectra of FeSO4.4H2O, two potential phase transitions have been identified from the changes in the lattice and water‐stretching regions. The resolution of the ν1(H2O) and ν3(H2O) bands in FeSO4·4H2O and FeSO4·H2O also improved sharply at low temperatures. The capability of distinguishing various forms of FeSO4 hydrates unambiguously makes the Raman technique a potential analytical tool for the identification of sulfate minerals on planetary surfaces. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
The first observation of pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material is reported. The system studied was the ordered antiferromagnet54Mn−MnCl2.4H2O. The response of the54Mn spins to a single pulse of variable length, the free induction decay, and Hahn spin-echo have all been observed. A discussion of the transverse decoherent relaxation timeT 2 in MnCl2.4H2O is given.  相似文献   

16.
The Raman spectra of synthetic compounds equivalent to the variscite group: FeAsO4·2H2O AlAsO4·2H2O, GaAsO4·2H2O, and InAsO4·2H2O are reported. In particular, upon comparison of FeAsO4·2H2O to AlAsO4·2H2O, it is observed that the Type II (weak) H‐bond lengths in the latter are slightly longer, which is postulated to affect the stability (As release) in water at pH 5 and 7. Arsenate stretching and bending vibrations were found to be distinct in terms of spectral structure and therefore well suited for fingerprinting. The calculated As O bond strengths from existing crystallographic data showed no significant variations. The strongest ν1 (AsO43−) stretch was used to monitor the As O bonding interactions in the four As O M units, where a shift of 114 cm−1 was observed in the order FeAsO4·2H2O (lowest) < InAsO4·2H2O < GaAsO4·2H2O < AlAsO4·2H2O (highest); this order also followed exactly the measured arsenic release of these phases. This shift in ν1 (AsO43−) position was rationalized to stem from the differences in the electronegativities of the M3+ cations. The trends mentioned above were verified and found to also hold for the isostructural phosphate analogues strengite (FePO4·2H2O) and variscite (AlPO4·2H2O) using published data. Therefore, it is postulated that, as observed with the stability of solution complexes, there may be a correlation between the electronegativity of the M3+ cation in these isostructural phases and their stability (As or P release) in water. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
18.
《Infrared physics》1988,28(3):189-194
The analysis of the IR and Raman spectra of the ion exchanger α-Zr(HPO4)2 · H2O and its half and fully exchanged phases, ZrKH(PO4)2 and Zr(NH4PO4)2 · H2O, have been reported. The splitting of the degenerate and nondegenerate modes indicates the presence of two crystallographically distinct anions in these compounds. The HPO2-4 ion has stronger P-O bond in ZrKH(PO4)2. One of the three crystallographically distinct water molecules in α-Zr(HPO4)2 · H2O can be considered as a free water molecule. The water molecules have significantly different hydrogen bond strengths. In Zr(NH4PO4)2 · H2O bands indicate the presence of two distinct NH+4 ions and water molecules. The PO3-4 ion in ZrKH(PO4)2 is linearly distorted.  相似文献   

19.
The electron paramagnetic resonance of VO2+ ion impurities has been studied in certain crystalline solids at ~ 9.45 GHz. VO2+ shows an isotropic spectra in Mg(ClO4)2·6H2O, RbBr, RbI, CsCl, thiourea, NH4HC2O4·12H2O and urea oxalate at room temperature, and has preferential orientation in MgSeO4·6H2O, KHC2O4, Rb2SO4 and (NH4)2M″(SeO4)2·6H2O (M″ = Zn, Co) single crystals. The line broadening of the EPR spectra of VO2+ in (NH4)2Co(SeO4)2·6H2O observed on cooling the crystal is explained on the basis of host spin lattice relaxation narrowing. The EPR spectra have been analysed and the spin-Hamiltonian parameters evaluated.  相似文献   

20.
Two novel ternary rare-earth complexes SmL5·L·(ClO4)2·7H2O and EuL5·L·(ClO4)2·6H2O (the first ligand L = C6H5COCH2SOCH2COC6H5, the second ligand L = C6H4OHCOO) were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DSC, 1HNMR and UV spectra. The detailed luminescence studies on the rare-earth complexes showed that the ternary rare-earth complexes presented stronger fluorescence intensities, longer lifetimes, and higher fluorescence quantum efficiencies than the binary rare-earth materials. After the introduction of the second ligand salicylic acid group, the relative emission intensities and fluorescence lifetimes of the ternary complexes LnL5·L·(ClO4)2·nH2O (Ln = Sm, Eu; n = 7, 6) enhanced more obviously than the binary complexes LnL5·(ClO4)3·2H2O. This indicated that the presence of both organic ligand bis(benzoylmethyl) sulfoxide and the second ligand salicylic acid could sensitize fluorescence intensities of rare-earth ions, and the introduction of salicylic acid group was a benefit for the fluorescence properties of the ternary rare-earth complexes. The fluorescence spectra, fluorescence lifetime and phosphorescence spectra were also discussed.  相似文献   

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