Magnetische Anregungen

Präsentation zum Thema: "Magnetische Anregungen"—  Präsentation transkript:

1 Magnetische Anregungen

2 Kristallfeld – übergänge
Mittelung über Polykristall

3 Beispiel NdCu2 Beispiel: NdCu2, orthorhombisch. Nd3+: J=9/2, Kramers-ion Neutronen können Übergänge zwischen den im Kristallfeld auf-gespaltenen Zuständen induzieren. Die Intensität einer Linie ist durch die die Matrixelemente von |<i|J|f>|2 bestimmt (|i>,|f> ....Kristallfeld-Anfangs und Endzustand des Nd ions).

4 NdCu2 - Kristallfeldanregungen
T=100 K T=10 K T=40 K

5 Magnonen – NdCu2 H=3T||b τ

6

7 Spinwellen (Magnonen)
153 a T=1.3 K Bohn et. al. PRB 22 (1980) 5447

8                                                                                                                        (a) Crystal structure of La2-2xSr1+2xMn2O7. The Mn ions are at the centre of the MnO6 octahedra. Circles denote La and Sr. (b) Expanded view of MnO6 octahedra in a single bilayer, showing the Mn d3z2 -r2  and dx2-y2  orbitals. Measured spin wave dispersion relations for x=0.35 and x=0.40. Solid lines show the best fits for the Heisenberg ferromagnet Hamiltonian with nearest neighbour exchange only. Dashed lines show the best fit including second neighbour interactions as well (i.e. hopping along Mn-O-Mn- O-Mn).

9 UO2:Spin wave dispersion curves measured at 16
UO2:Spin wave dispersion curves measured at 16.5 K along the principal crystallographic directions. Dashed lines and crosses correspond to acoustic phonon branches. Open symbols indicate qualitatively smaller magnon intensity than the filled points. The non-spin-flip cross-section was always found to be negligible.