Neutron spin-polarized neutrons

It is a somewhat surprising fact that information about vibrational frequencies and bond lengths in very common and important ions is very sparse. Clearly, many more such determinations are necessary. Only this year, for example, have data become available which enable metal-ligand displacements on electron removal for the aquo Fe(II)/Fe(III) and Co(II)/Co(III) systems to be obtained. In view of the importance of these partially unpublished data, I have reproduced them in Table VI. The values of A for the Fe and Co systems are 0.128-0.137, and 0.208 8 respectively. The variability of the Fe results points to the fact that caution must be exercised in using data obtained in crystal lattices for a solution environment. Spin-polarized neutron diffraction studies on the structure of solu-... 

The internal iron (III) ions are octahedrally coordinated by the two oxides and four hydroxo bridges. The outer iron(III) ions coordinate three nitrogens and three hydroxyls. Spin polarized neutron scattering showed that all Fe ions have a spin 5/2, six spins up and two down [23]. This rationalizes the S = 10 spin ground state that is in agreement with magnetization measurements. 

Papoular, R.J. and Gillon, B. (1990) Maximum entropy reconstruction of spin density maps in crystals from polarized neutron diffraction data, Europhys. Lett., 13(5), 429 134. 

In order to figure out the FWs, the nuclear structure was refined from unpolarized neutron data taken at 30 K, in the paramagnetic state, on a 4-circle diffractometer. Furthermore, a set of 248 flipping ratios was measured with polarized neutrons at 1.6 K, with the spin density long range ordered by a 4.65 T applied magnetic field. 

Baron, V., Gillon, B., Plantevin, O. et al. (1996) Spin-density maps for an oxamido-bridged Mn(II)Cu(II) binuclear compound. Polarized neutron diffraction and theoretical studies, J. Am. Chem. Soc., 118, 11822-11830. 

Zheludev, A., Grand, A., Ressouche, E. et al. (1994) Experimental determination of the spin density in the tetracyanoethenide free radical, [TCNE]-, by single-crystal polarized neutron diffraction, a view of a 71 orbital, J. Am. Chem. Soc., 116,7243-7249. 

Zheludev, A., Bonnet, Luneau, D. et al. (1995) The spin density in an imino nitroxide free radical a polarized-neutron study, Physica B, 213-214, 268-271. 

We report herein a single crystal polarized neutron investigation of the spin density of two purely organic nitronyl nitroxide free radicals which present ferromagnetic interactions the 2-(6-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-... 

The motion of the neutron polarization P(t) - the quantum mechanical expectancy value of neutron spin - is described by the Bloch equation... 

Fig. 2.1 Spin history leading to the formation of the spin-echo. Longitudinally polarized neutrons enter from the left. Upper part spin motion. Lower part NSE setup, Ti/2-flipper between belonging current rings, primary main precession solenoid l symmetry scan...

The joint use of X-ray and neutron diffraction data is particularly expedient. Firstly, the interaction between the magnetic moments of neutrons and electrons is the basis for polarized-neutron diffraction, from which the unpaired spin density in a system can be derived. The diffraction of spin-polarized neutrons is an important technique, beyond the scope of this volume. Secondly, the interaction between neutrons and the atomic nuclei, which is the basis for structure determination by neutron diffraction, leads directly to information on the positions and mean-square vibrations of the nuclei. 

A detailed study of the spin density and bonding of the [CrFel3- ion in K3[CrF6] has appeared.1067 The results of polarized neutron diffraction experiments1068 were reinterpreted. A chemically based model of the [CrF6]3- ion has been fitted to the 92 observed magnetic structure factors by a least squares procedure. The spin density in the chromium(III) orbitals has t2g symmetry 06spin density centred on the... 

Figure 6. Polarized neutron reflectivities of fN 0 = 5 nm, 20 nm and 60 nm samples during the reversal process. The spin flip (R+, R +) and non spin flip (if4-1", R") reflectivities are simultaneously modeled to obtain the magnetization configuration as shown in the inset. The lines are the computed reflectivities for different scattering cross-sections based on this model.

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