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Magnetostructural-transition related multifunctionality in martensitic Heuslers

• M. Acet

Experimentalphysik, Universität Duisburg-Essen

Elemental properties of Fe and Mn Martensitic transformations and Heuslers Magnetic interactions in martensitic Heuslers Outline

Structure of the transition elements and elements with wrong crystal structures

complex cubic bcc hcp hcp bcc fcc

Allotropy in the 3d elements

s+d electrons 6 7 8 9 10

fcc Mn fcc Fe

Rigid band model and the Slater-Pauling curve: Valence electron concentration dependence of the magnetic moment

Structure and phase diagrams of Ni-Mn-Z (Z: Ga, In, Sn, Sb)

L21 L10 10M

(5M)

14M

(7M)

(e/a): Concentration weighted number of s+d (3d elements) + s+p (main group)

Heusler alloys Shape memory (nonmagnetic martensite)

Cu-Ni-Al Cu-Zn-Al

Magnetic field induced Structural modifications (magnetic martensite)

Ni-Mn-Ga Co-Mn-Al Ni-Mn-In

Magnetocaloric effect

Ni-Mn-Ga Ni-Mn-Sn Ni-Mn-In

Electron spin polarization

half metallic properties in ferromagnetic Heuslers

Some features of Heusler alloys

The magnetization of Ni-Mn-Z (Z: Ga, In, Sn, Sb)

Why does M(T) drop? Why is the FM transition smeared

• ver the temperature?

Extended Slater-Pauling curve

Martensitic transformation takes place for dMn-Mn ~ 3 Å: Is there any relationship between the martensitic transformation and the onset of AF-exchange?

Mn-Mn separation and the martensitic transformation in Heuslers

Complementary Neutron polarization analysis Ferromagnetic resonance

q0/2

intensity q (Å-1)

q0

   sin 4  q

monochrometer array polarizer flipper sample detector banks with analyzers XYZ coils incident neutrons

D7

XYZ polarization analysis and neutron depolarization (D7/ILL)

tot = coh + incoh + mag Polarization analysis

flipper  analyzer/detector OFF 1 polarizer neutrons ON

Neutron depolarization and the flipping ratio (Rf )

 

   n n R f 1 1

sample

Magnetization and flipping ratio

Ni-Mn-Sn and Ni-Mn-Sb

Ms

Ni-Mn-Sn: polarization analysis

Neutron depolarization Magnetic scattering

Ni-Mn-Sb: polarization analysis

Tg=3.3 K

c b a 14M

?

c a L21

Moment configurations in austenite and martensitie

Summary

Drop in M(T) caused by disappearance

• f FM coupling

TC(M) denotes the onset of FM and AF-like ordering Mn and antiferromagnetism and Ms

Ferromagnetic resonance (FMR)

0Hres = /  PM 0Hres < /  FM 0Hres  AF : instrument microwave frequency : gyromagnetic ratio

A res

H H      

) 2 (

A E A res

H H H H       

Ferromagnetic resonance

The magnetization of Ni-Mn-Z (Z: Ga, In, Sn, Sb)

M(T) in 5 mT M(T) in 5 T

Conclusions

FM and AF correlations coexist at T > Ms and beyond TC

A

FM correlations disappear below Ms but AF short-range correlations persist down to lowest temperatures

SPP 1239

• O. Posth, M. Gruner, P. Entel

Universität Duisburg-Essen

• L. Mañosa, A. Planes

Universitat de Barcelona

• P. P. Deen

Institut Laue-Langevin

• X. Moya

University of Cambridge

• T. Krenke

ThyssenKrupp Electrical Steel

• A. Senyshyn, S. Ener, J. Neuhaus, W. Petry

TU-München & FRM II

• S. Aksoy

Istanbul Technical University

L21 Ni Mn Sb

Magnetic exchange constants in Ni-Mn-Sb

Ni50Mn40Sb10

Ni-Mn-Sn and Ni-Mn-Sb (magnetic scattering)

Ni-Mn-Sn (coherent scattering)

D2B  = 1.594 Å D7  = 4.83 Å

Ms and TC as a function of valence electron concentration

• L. Mañosa et al., APL 92, 012515 (2008).

Pressure-dependence of magnetization in Ni-Mn-In

• T. Krenke, Thesis (Duisburg, 2007).

Austenitic state lattice constant at room temperature in Ni-Mn-Z

7.87

Fe50Ni30Mn20 (TN = 300 K)

Coexisting FM and AF correlations in Fe-Ni-Mn

1.54 T = 100 K ferromagnetic correlations antiferromagnetic ordering T = 300 K T = 400 K antiferromagnetic correlations

Magnetization of Ni-Mn based Heuslers

• A. Planes et al. J. Phys.: Condens. Matter 21, 233201 (2009)

Mn-Mn: 4.25 Å