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TABLE 1 Structural parameters of N,N’-dioxy-1,3,5,7-tetramethyl-2,€ diazaadamantane Crystallographic system: monoclinic, space group C2/c. Lattice parameters (A): a=8.371, b=14.482, c=10.329, B°=105.35. R values for fit: R=0.037, R,=0.035. * Ueq = (U1U2U3)”" is the equivalent isotropic thermal parameter. We used the anisotropic thermal parameters to refine the atom positions. (i), (ii), (iii), (iv) and (v) refer to the following equivalent positions relative to the x, y, z set: (J=1-—x, y, 1/2-z (i)=1-—x, 1-y, 1—-z (iii) =3/2—x, 1/2—y,1-z lw)=x,1-y, -1/2+2 W)=x,1-y, 1/2 +2

Table 1 Structural parameters of N,N’-dioxy-1,3,5,7-tetramethyl-2,€ diazaadamantane Crystallographic system: monoclinic, space group C2/c. Lattice parameters (A): a=8.371, b=14.482, c=10.329, B°=105.35. R values for fit: R=0.037, R,=0.035. * Ueq = (U1U2U3)”" is the equivalent isotropic thermal parameter. We used the anisotropic thermal parameters to refine the atom positions. (i), (ii), (iii), (iv) and (v) refer to the following equivalent positions relative to the x, y, z set: (J=1-—x, y, 1/2-z (i)=1-—x, 1-y, 1—-z (iii) =3/2—x, 1/2—y,1-z lw)=x,1-y, -1/2+2 W)=x,1-y, 1/2 +2

Related Figures (6)

FIG. 1 a, Structure of the NNV’-dioxy-1,3,5,7-tetramethy!-2,6-diazaadaman- tane molecule showing the two NO radicals in opposite positions. 6, The This biradical (Fig. la) was prepared because an intra- molecular ferromagnetic interaction between the two orthogonal N-O groups of the molecule could be expected on symmetry considerations (an unpaired electron is nearly localized on each NO radical)*'®. In the crystal (Table 1; Y. Dromzee, Y. Jeannin, R.C. and A.R., manuscript in preparation) each NO group has three close NO neighbours, one on the other side of the same suggesting a three-dimensional network of chains interconnec- ted through inter- and intramolecular interactions. The static susceptibility (above 2K) is characteristic of ferromagnetic interactions’ with a positive Curie-Weiss temperature (@ = 10 K) extrapolated from a temperature T > 150K. In the same poly- crystal, yT (where y is magnetic susceptibility) increases when T decreases from 10 K down to 2 K, and the magnetization, M, tends to saturate (87% of the expected saturation value) at 4.2 K
FIG. 1 a, Structure of the NNV’-dioxy-1,3,5,7-tetramethy!-2,6-diazaadaman- tane molecule showing the two NO radicals in opposite positions. 6, The This biradical (Fig. la) was prepared because an intra- molecular ferromagnetic interaction between the two orthogonal N-O groups of the molecule could be expected on symmetry considerations (an unpaired electron is nearly localized on each NO radical)*'®. In the crystal (Table 1; Y. Dromzee, Y. Jeannin, R.C. and A.R., manuscript in preparation) each NO group has three close NO neighbours, one on the other side of the same suggesting a three-dimensional network of chains interconnec- ted through inter- and intramolecular interactions. The static susceptibility (above 2K) is characteristic of ferromagnetic interactions’ with a positive Curie-Weiss temperature (@ = 10 K) extrapolated from a temperature T > 150K. In the same poly- crystal, yT (where y is magnetic susceptibility) increases when T decreases from 10 K down to 2 K, and the magnetization, M, tends to saturate (87% of the expected saturation value) at 4.2 K
crystals consist of interconnected chains which, given the similar distances between NO near neighbours, may make up a three-dimensional network. For the present measurements, single crystals (in the shape of long transparent parallelepipeds with a yellow-orange colour) were prepared as described in ref. 9. No impurities could be detected, except for traces of monoradicals appearing in the frozen electron spin resonance (ESR) spectrum and estimated by spectral reconstitution to be 0.6%. We studied the magnetic properties in low and high magnetic fields, and temperatures between 50mK and room temperature. The ferromagnetic transition is characterized by a divergence of the a.c. susceptibil- ity, and the onset of spontaneous magnetization at 1.48 K. At
crystals consist of interconnected chains which, given the similar distances between NO near neighbours, may make up a three-dimensional network. For the present measurements, single crystals (in the shape of long transparent parallelepipeds with a yellow-orange colour) were prepared as described in ref. 9. No impurities could be detected, except for traces of monoradicals appearing in the frozen electron spin resonance (ESR) spectrum and estimated by spectral reconstitution to be 0.6%. We studied the magnetic properties in low and high magnetic fields, and temperatures between 50mK and room temperature. The ferromagnetic transition is characterized by a divergence of the a.c. susceptibil- ity, and the onset of spontaneous magnetization at 1.48 K. At
FIG. 2 Alternating current susceptibility (y’ is the real part and y” is the imaginary part), showing the divergence of y’ when 7 approaches 7, from above and its saturation close to 1/N. the inverse of the demagnetizing field factor. Note the different scale for y", which indicates the existence. of very weak magnetic losses below 7, ("/x' = 0.01).
FIG. 2 Alternating current susceptibility (y’ is the real part and y” is the imaginary part), showing the divergence of y’ when 7 approaches 7, from above and its saturation close to 1/N. the inverse of the demagnetizing field factor. Note the different scale for y", which indicates the existence. of very weak magnetic losses below 7, ("/x' = 0.01).
FIG. 3 a, Low-field magnetization. This is linear in a low applied field (exactly compensated by the demagnetizing field) and shows the onset of spon- taneous magnetization below 1.48 K. The inset shows the temperature dependence of the spontaneous magnetization taken at the departure from linearity of the M(H) isotherms. b, The low-field hysteresis cycle at 1.3 K (0.8 K for the inset) has no detectable hysteresis (within 0.1 Oe). very low temperatures the saturation magnetization gives the expected value for two electrons with spin 4 per molecule. Surprisingly, no hysteresis could be detected.
FIG. 3 a, Low-field magnetization. This is linear in a low applied field (exactly compensated by the demagnetizing field) and shows the onset of spon- taneous magnetization below 1.48 K. The inset shows the temperature dependence of the spontaneous magnetization taken at the departure from linearity of the M(H) isotherms. b, The low-field hysteresis cycle at 1.3 K (0.8 K for the inset) has no detectable hysteresis (within 0.1 Oe). very low temperatures the saturation magnetization gives the expected value for two electrons with spin 4 per molecule. Surprisingly, no hysteresis could be detected.
FIG. 4 High-field magnetization at temperatures of 4.20, 1.64, 1.04, 0.50 and 0.10 K gives the expected total saturation which could not be reached in previous experiments at 4.2K and in a field of 5T (ref. 9). The inset (for T=0.1 K) confirms that no hysteresis is observed even after applying a 14-T field. The low-field measurements are thus characteristic of ferro- magnetic behaviour (divergence of the a.c. susceptibility and onset of spontaneous magnetization at 1.48 K) but have two particular features: the absence (or very small value) of hyster- esis and the similar values for d.c. and a.c. susceptibilities. Magnetization measurements with the field perpendicular to the
FIG. 4 High-field magnetization at temperatures of 4.20, 1.64, 1.04, 0.50 and 0.10 K gives the expected total saturation which could not be reached in previous experiments at 4.2K and in a field of 5T (ref. 9). The inset (for T=0.1 K) confirms that no hysteresis is observed even after applying a 14-T field. The low-field measurements are thus characteristic of ferro- magnetic behaviour (divergence of the a.c. susceptibility and onset of spontaneous magnetization at 1.48 K) but have two particular features: the absence (or very small value) of hyster- esis and the similar values for d.c. and a.c. susceptibilities. Magnetization measurements with the field perpendicular to the
Boron isotope compositions are reported as per mil (%) deviations in the 4B/*°B ratio from NBS 951. Pore fluids were sampled using standard squeezing methods and concentrations were determined by colorimetry??:?3, All isotope ratios were determined by thermal ionization mass spectrometry as the negative molecular ion, BO3, following the whole sample integration method of You et a/.**. For foraminifera, the uncertainty of isotopic composi- tions is ~1%., based on the analysis of parallel samples, and 0.6% for pore fluids based on duplicate seawater analyses. Actual scatter in the pore fluid data is slightly larger, most probably because of adsorption/desorption effects associated with sampling . mbsf, metres below sea floor.
Boron isotope compositions are reported as per mil (%) deviations in the 4B/*°B ratio from NBS 951. Pore fluids were sampled using standard squeezing methods and concentrations were determined by colorimetry??:?3, All isotope ratios were determined by thermal ionization mass spectrometry as the negative molecular ion, BO3, following the whole sample integration method of You et a/.**. For foraminifera, the uncertainty of isotopic composi- tions is ~1%., based on the analysis of parallel samples, and 0.6% for pore fluids based on duplicate seawater analyses. Actual scatter in the pore fluid data is slightly larger, most probably because of adsorption/desorption effects associated with sampling . mbsf, metres below sea floor.
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