Tham khảo tài liệu 'neutron scattering from magnetic materials part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Spherical neutron polarimetry 237 Fig. 10. The h0l section of reciprocal space forthe incommensurate structure of CuO. The fundamental nuclear reflections are shown as open circles and the magnetic satellites as filled ones. The scattering vectors for the 002 T and 000 T reflections are shown as dashed lines. . Magnetic structures with zero propagation vector It has already been pointed out in Section that in structures with T 0 nuclear and magnetic scattering occur in the same Bragg reflections and interference between them can occur. In this case SNP can determine the ratio between magnetic and nuclear scattering allowing the magnitude of magnetic moments to be established from SNP alone without recourse to supplementary integrated intensity measurements. . The magnetic structure of U14Au51. The intermetallic compound U14Au51 crystallises in the hexagonal Gd14Ag51 structure with space group P6 m 11 . The uranium atoms occupy three crystallographically distinct sites 6 k 6 j and 2 e labelled U1 U2 and U3 respectively. Susceptibility specific heat and resistivity indicate a magnetic phase transition at 22 K. This has been confirmed by neutron powder diffraction measurements an antiferromagnetic structure with zero propagation vector and magnetic space group P6 m was proposed 12 . The ordered magnetic moments aligned parallel to c were and B onU1 andU2 respectively. No moment was assigned to theU3 atoms which have a particularly small separation it was argued that direct f -electron wave function overlap prevents a magnetic response. An SNP study of the magnetic structure was undertaken because it proved impossible to reconcile the intensity of magnetic scattering by single crystals of U14Au51 with the proposed magnetic structure. The U14Au51 crystal was mounted with its axis vertical. The polarisation matrices determined for the and reflections are given in Table 1. They enable severe constraints to be imposed on the possible
