tailieunhanh - Neutron Scattering from Magnetic Materials part 8

Tham khảo tài liệu 'neutron scattering from magnetic materials part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 206 J. Schweizer magnetic scattering shows that a large fraction of the magnetic moments are not aligned along the applied magnetic field but is canted away from the field direction. The randomly directed strong crystalline fields in the amorphous material has the effect that the applied field can orient only the component of the magnetic moment that is parallel to it. Moreover some correlations exist between the directions of crystalline fields in adjacent cells enough to produce a ferromagnetic short-range order of the transverse components of the magnetic moments. A more subtle arrangement of the transverse components is met in magnetically ordered amorphous materials which contain rare-earth atoms associated with a transition metal. In these systems with two types of magnetic atoms the huge anisotropy of the rare earth plays a fundamental role. For instance in the Er-Co amorphous alloys the cobalt moments are ferromagnetically coupled and are parallel to one another aligned by the external field and the Er moments are on the average antiparallel to the Co moments but strongly correlated to the local crystal field axes in spite of the fact that these axes are distributed in all directions. Such a structure with rare-earth moments distributed in space but still more or less antiparallel to the cobalt moments has been called sperimagnetic 52 . The rare-earth moments are also aligned when a magnetic field is applied but only partly because of their magnetic interaction with the cobalt moments the magnetic anisotropy very large at low temperatures prevents the alignment from being complete. Concerning their transverse components are they randomly distributed or are they correlated The question has been answered by a uniaxial polarization analysis experiment 53 . In this experiment the polarization was parallel to the scattering vector with a horizontal field of T enough to align the magnetization of the sample. The non-spin-flip and the spin-flip scattering at .

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