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

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Bestimmung von Formfaktoren: polarisierte Neutronen Formfaktor

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Atomgitter Magnetisches Gitter Ferromagnet Antiferro- magnet Überstruktur - reflexe

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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

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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

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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.

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NdCu2

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

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AF2 Pattern T=4.1K H=0T

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NdCu2 Magnetic Structures at T=0

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

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Komplexere Strukturen F2

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

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