Polarized neutron studies

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. 

For a long time, sample size has limited the use of some investigation techniques. For example, polarized neutron studies failed in part for sample-size problems (see Section XII.C). Similarly, to perform neutron inelastic scattering experiments on TTF-TCNQ, Shirane et al. [73] had to use an assembly of 17 aligned crystals to reach a total volume of about 0.015 cm3. Of course, there is a gradual improvement in both measurement techniques and crystal growth, but almost every time a new type of material is found, problems recur. In this section we first recall the needs of the main crys-... 

Experimental values of Fe moments in Y2Fe14B as obtained by means of polarized neutron studies (Givord et al. 1985d) and 57Fe Mossbauer effect measurements (R. Fruchart et al. 1987) are given in the first and second line of table 13. In the bottom part of the table results of three different types of band structure calculations are given. 

Comparision of the Fe moments at the six Fe sites in R2Fe14B obtained by polarized neutron studies and 57Fe Mossbauer spectroscopy with those derived from band structure calculations. All values are given in Bohr magnetons per Fe atom. 

Using the experimental (rt) integral derived from polarized-neutron studies of the magnetic form factor of Tm metal. 

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. 

Gillon, B. Schweizer, J. (1989) Study of chemical bonding in molecules the interest of polarized neutron diffraction, In Molecules in Physics, Chemistry and Biology, Maruani, Jean(Ed.), Kluwer, Dordrecht, The Netherlands, Vol. II, p. 111. 

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 In view of the importance of these partially unpublished data, I have reproduced them in Table VI.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-... 

Ketonate complexes of Ru are reported in a number of papers. The parent complex [Ru(acac)3] has been subject to a polarized neutron diffraction study at 4.18 K, to powder neutron diffraction studies and to single-crystal structure determinations at 293 K, 92 K, and 10.5 K. The structure is disordered at all temperatures. Measurements of the magnetic susceptibilities (at 2.5 K and 300 K) have been made along different crystal axis directions, and the results analyzed. An investigation of the relationships between ionization potentials and half-wave potentials of a series of tris(/3-ketonate)Ru complexes has been reported, and the electrochemical properties of [Ru(acac)3] in chloroaluminate molten salt media have been reported. The reduced species [Ru(acac)3] can react with AICI4 reduction by bulk electrolysis of a small amount of [Ru-(acac)3] in the melt yields [RuClg]. ... 

Detailed studies - band structure calculations, de Haas-van Alphen effect and polarized neutron diffraction - have evidenced the strong hybridization of 5 f bands either with p anions bands (USi3, UGes, USns) or 4d bands (URhs, UIts). 

PuP amongst compounds of metallic character, plutonium pnictides PuP, PuAs, PuSb are ferromagnetic. PuP has been studied not only by the magnetization technique but also by neutron diffraction specific heat and Powder polarized neutron... 

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... 

Abstract We use polarized neutron reflectivity to study the evolution of the... 

The X-ray and neutron diffraction data mentioned previously have been used in conjunction with the technique of polarized neutron diffraction (at 4.2 K) to deduce spin-density distributions in [MnPc].519,520 In further investigations514 it proved possible to determine individual 3d and 4s orbital populations on the manganese ion together with an estimate of 24% for the d-orbital electron density delocalized in the macrocyclic ring. From these studies it appears that the charge on the manganese is approximately +1 this charge appears to be achieved primarily by the loss of a 3d electron rather than a 4s electron. 

In the case of structural studies with x-rays, sample size is rarely a serious problem since single crystals as small as about 0.001 mm3 (sealed x-ray tube) or 10-9 mm3 (synchrotron radiation) will do. In the case of x-ray diffuse scattering measurements with the assembly described in Section VI.D, the crystal must be 2 mm long at least but can be relatively thin. With neutrons, however, sample size is more critical. Indeed, for structure measurements, 0.1 mm3 is a minimum, with the highest neutron fluxes available nowadays, and more usual sizes are in the range of several cubic millimeters to several tens of cubic millimeters. For polarized neutrons or inelastic scattering studies, much larger samples are necessary. 

Polarized neutron diffraction makes it possible to measure magnetic structure factors and thus to obtain the distribution of unpaired spins in magnetic materials (see, e.g., Ref. 201). Let us discuss here the use of this technique for the study of low-dimensional organic conductors. 

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