Transcript Folie 1

Metallic magnetism and Invar
M. Acet
Experimentalphysik, Universität Duisburg-Essen
Outline
- Structure of transition metals
- Magnetism of transition metals
- Magnetic instabilities and ‘Invar’
Band formation
Structure of the transition elements
crystal structures)
complex cubic
hcp
bcc
(elements with ‘wrong’
bcc
fcc
hcp
Allotropy in the 3d elements
The density of states and non-integral magnetic moment
N  8
BCC Fe
N  N  2.2 B
Ferro and antiferromagnetic transition temperatures
-Mn
Rigid band model and the Slater-Pauling curve:
Valence electron concentration dependence of
the magnetic moment
fcc Mn
fcc Fe
s+d electrons
6
7
8
9
10
Invar: Fe65Ni35
l  l 0(1  T )
Measuring the thermal expansion of the Eifel tower
Thermal expansion of solids
invar
‘normal’ metals
T (K)
Binding Binding
energy energy
vs. atomic
“normal”
vs. volume
atomic for
volume
for and
magnetically
unstable
ferromagnet
(schematic)
a “normal”
ferromagnet
(schematic)
Ground state
 ~ 2 B
Low Moment
High Moment
Magnetic moment
Energy
"normal" 3d ferromagnet
 ~ 0

T (K)
E
Vc
enhanced “negative”
anharmonicity
V0
Atomic volume
What are instabilities at all?
Fe-Ni: Invar to Anti-invar
Summary of Magnetovolume
Instabilities
“anti-Invar”
“Invar”
Anti-invar in fcc-Fe and fcc-Mn
Moruzzi et al, PRB 39 (1989)
Ferromagnetic Mn in a cubic environment
Cu2MnAl
Cu2MnSn
Mn3SnC
MnBi
MnAl
Ag5MnAl
Mn3ZnC
Au4Mn
MnSb
MnCrSb
Pt3Mn
Ni3Mn
…
…
Knowledge of magnetostructural
properties vital for material design in
- Spintronics
- Magnetic shape memory
- Nanomagnets