Magnetic Diffraction

'

'*'1

)(jj

iijjcoh

elnuc

jjeebbN

S RκRκ

),('

),()ˆˆ('

'

2

2

22

κκκκ nucmag S

k

kNS

mc

e

k

kN

dEd

d

'

''21

'21 )()(

1)( jj ii

TjjTjjj

j

elmag eeJgFJgF

NS RκRκ

Difference to nuclear scattering: Formfactor ... no magnetic signal at high angles

Polarisationfactor ... only moment components normal to κ contribute

j

gF )(21

)ˆˆ( κκ

Bestimmung von Formfaktoren: polarisierte Neutronen

Formfaktor

)(2

)()( 20 jg

gjF

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).

TN=122K

TN= 42 K M [010]TR= 10 K q = (2/3 1 0) Magnetic Structure from

Neutron Scattering

GdCu2

Rotter et.al. J. Magn. Mag. Mat. 214 (2000) 281

Magnetic Diffraction using Laue Method (LADI – ILL)

4% Ga doped FeGe2

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)

lτ 3τ5τ

AF2 Pattern

T=4.1KH=0T

NdCu2 Magnetic Structures

at T=0

Pattern T=0

h0.4 0.6 0.8 1.0

AF1

F1

F2

F3

τ=(0.6 0 0)5τ3τ

τ=(0.6666 0 0)

τ=(0.625 0 0) 2τ

2τ

2τ

k

Komplexere Strukturen

F2

|κ|[Å-1]

I(κ)

[co

unts

]

nichtkollineare Struktur(mcphase)

GdCu2In