Magnetic Diffraction Difference to nuclear scattering: Formfactor... no magnetic signal at high angles Polarisationfactor... only moment components normal to κ contribute

Bestimmung von Formfaktoren: polarisierte Neutronen Formfaktor

Atomgitter Magnetisches Gitter Ferromagnet Antiferro- magnet Überstruktur - reflexe

In 1951 Shull showed the magnetic structure of the MnO crystal, which led to the discovery of antiferromagnetism (where the magnetic moments of some atoms point up and some point down). T N =122K

T N = 42 K M [010] T R = 10 K q = (2/3 1 0) Magnetic Structure from Neutron Scattering GdCu 2 Rotter et.al. J. Magn. Mag. Mat. 214 (2000) 281

Magnetic Diffraction using Laue Method (LADI – ILL) 4% Ga doped FeGe 2 This material undergoes a number of trans- itions and below 180K it locks into a non- harmonic spiral phase with a propagation vector of exactly 1/10. This gives rise to additional Bragg-peaks, which are shown in the second picture.

NdCu2

mehrere Kristallite (ca 120° verdreht) l τ 3τ3τ 5τ5τ

AF2 Pattern T=4.1K H=0T

NdCu2 Magnetic Structures at T=0

Pattern T=0 h AF1 F1 F2 F3 τ=( ) 5τ5τ3τ3τ τ=( ) τ=( ) 2τ2τ 2τ2τ 2τ2τ k

Komplexere Strukturen F2

|κ|[Å -1 ] I(κ) [counts] nichtkollineare Struktur(mcphase) GdCu 2 In