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Tham khảo tài liệu 'neutron scattering from magnetic materials part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 176 J. Schweizer Fig. 8. Enaminoketon CigH2sO2N2Cu NO 2 spin density projection along the axis 24 a T 40 K contour step 0.008 b Â2 b T 4 K contour step 0.090 b Â2. striking fact is the quasidisappearance of the spin density on N2O2 and N6O6. These two NO groups belong to the two different molecules N2O2 to molecule A and N6O6 to molecule B. They are facing each other at a distance of 3.40 Â. It is obvious that the negative coupling between adjacent molecules revealed by the drop of the magnetic susceptibility corresponds actually to a negative coupling between these two spin carriers which provokes an almost complete dimerization of their spins. 4.2.3. Modeling the magnetic wave function. A convenient way to retrieve the spin density distribution while avoiding the problems due to Fourier inversion is to model the spin density and to determine the parameters involved in the model by a refinement procedure from the experimental data. A first and natural model to represent a spin density is to consider it as the square of the wave function of the magnetic electrons. The structure factor can be expressed by Fm V eiQ f V eiQrw d3r. 78 V is in the general case a molecular wave function 1 22 aJ pj atoms Polarized neutrons and polarization analysis 177 where the sum runs over all the magnetic atoms. Two types of terms enter the expression of FM one center integrals Ị pjeiQrpjd3r 79 which represent the main contribution two center integrals p eiQtpj d3r 80 which are correcting terms corresponding to the overlap between the wave functions of neighboring atoms. In the following we will restrict ourselves to the one center integrals considering the magnetic amplitude scattered by one atom only. We shall express this amplitude in term of magnetic form factor and we shall consider successively the case of p and d electrons with a magnetic moment which is mainly of spin origin and the case of f electrons rare earths and actinides where spin and orbit couple together to give a .
