Metallic magnetism and Invar M. Acet Experimentalphysik, Universität Duisburg-Essen

- Structure of transition metals - Magnetism of transition metals - Magnetic instabilities and ‘Invar’ Outline

Band formation

Structure of the transition elements (elements with ‘wrong’ crystal structures) complex cubicbcchcp bccfcc

Allotropy in the 3d elements

The density of states and non-integral magnetic moment N   N   2.2  B  N  8 BCC Fe

Ferro and antiferromagnetic transition temperatures  -Mn

s+d electrons fcc Mn fcc Fe Rigid band model and the Slater-Pauling curve: Valence electron concentration dependence of the magnetic moment

Invar: Fe 65 Ni 35

Measuring the thermal expansion of the Eifel tower

Thermal expansion of solids ‘normal’ metals invar T (K)

Binding energy vs. atomic volume for a “normal” ferromagnet (schematic) Binding energy vs. atomic volume for “normal” and magnetically unstable ferromagnet (schematic) enhanced “negative” anharmonicity T (K)

What are instabilities at all?

Fe-Ni: Invar to Anti-invar

Summary of Magnetovolume Instabilities positive enhanced anharmonicity negative enhanced anharmonicity “anti-Invar” “Invar”

Moruzzi et al, PRB 39 (1989) Anti-invar in fcc-Fe and fcc-Mn

Cu 2 MnAl Cu2MnSn Mn 3 SnC MnBi MnAl Ag 5 MnAl Mn 3 ZnC Au 4 Mn MnSb MnCrSb Pt 3 Mn Ni 3 Mn … Knowledge of magnetostructural properties vital for material design in - Spintronics - Magnetic shape memory - Nanomagnets Ferromagnetic Mn in a cubic environment