Recent developments of understandingthe magnetic shape memory effect in

Ni-Mn-Ga alloysI. Aaltio, O. Söderberg, Y. Ge, O. Heczko and S.-P. Hannula

TKK, Helsinki University of TechnologyDepartment of Materials Science and Engineering

Lab. of Materials ScienceP.O. Box 6200, 02015 TKK, Finland

Contents

• Magnetic Shape Memory (MSM) effect and MSM materials

• Ni-Mn-Ga alloys and their properties• Recent research trends and developments• Research of MSM materials at TKK

MSM actuation

H = 0

σreturn

H=H2> H1

σreturn = 0

H = 0

Leng

thl

H = H1H=H3> H2

H = Hsat H = H2H = 0

σreturnσreturn

σreturnσreturn σreturn

σreturn

Twinboundary

Twin variant B

ca

bca

bc < aa

b (=a)

unit cellTwin variant A

H = 0

σreturn= 0

Actuation sequence

Actuation:Repeated deformation

The easy axis of magnetization is the same as the short crystalline c-axis of the modulatedmartensite (in the cubic phase coordinate system).

Freturn

MFI Force: Fmag

coils

Pushrod

MSM element

Fext

H

MSM compared to other actuator materials

MSM is potentially suitable for: • Producing motion and force

(from DC…1 kHz)• Vibration damping (controllable

stiffness)• Producing electric energy (by inverse MSM

effect)

piezo- magnetostrictive MSM (5M) MSM (7M)0

2

4

6

8

10

max

imum

stra

in (%

)

piezo- magnetostrictive MSM (5M) MSM (7M)0

1020304050607080

max

imum

stre

ss (

MP

a)

piezo- magnetostrictive MSM (5M) MSM (7M)0,00

0,02

0,04

0,06

0,08

0,10

0,120,14

0,16

spec

ific

ener

gy (M

J/m

3 )

Graphs: Oleg Heczko

MSM effect in different alloys

MSM has been observed in several alloys, such as:•Fe-Pd•Fe-Pt•Ni-Mn-Al•Co-Ni-Ga•Co-Ni-Al•Ni-Fe-Ga•Co-Ni

NiNi--MnMn--GaGa::LargeLarge magneticmagnetic fieldfield inducedinducedstrainstrain (MFIS) (MFIS) (6 % (6 % oror 10 %)10 %)LargeLarge eneryenery productproduct (MFI (MFI forceforce x x strainstrain): ): 300 MPa x 300 MPa x μμm/mmm/mmModerateModerate fieldfield strengthsstrengthsneededneeded(H(H≤≤0.5 T)0.5 T)

LargeLarge magneticmagnetic anisotropyanisotropyTwinnedTwinned martensite martensite structurestructureHighHigh mobilitymobility of of twintwin boundariesboundaries

Expensive raw materials

Small magnetic field inducedstrain MFIS (appr. 0,1%)

Works only under zero deg. C

Small MFIS

K. Ullakko, PCT FI960/00410; K. Ullakko, J. K. Huang, C. Kantner, and R. C. O’Handley, Appl.Phys.Lett.69 (1996), 1966.

Inferior repeatability

Ni-Mn-Ga MSM materials

Ni

Mn

Ga

Single crystal: largest MFIS

Polycrystal: small MFIS

MartensiteModulation Max Max.

MFIS twinning(%) strain

(%)10M (5M) primarily tetragonal 6 6

(monoclinic)14M (7M) orthorombic 10 10NM (T) tetragonal 0 18-20

Cubic austenite: no MFIS, but superelasticity ~5 %

•Chemical composition•Heat treatments•External temperature•External load•External magn. field

•Production method•Crystallization

MFIS -magnetic field induced strain

Twin boundary motion and atomictransitions

M. Han, J.C. Bennett, M.A. Gharghouri, J. Chen, C.V. Hyatt, Understanding modulated twin transition at the atomic level,Acta Materialia 55 (2007) 1731–1740

Twin structure of Ni-MnGa

TEM images: Y. Ge

The step type

Crossing type

Bright field image of Ni49.5Mn28.6Ga21.9 alloy. The insets are selected-area electron diffraction patterns from both sides of interface and the interface area.

Magnetic properties

Limiting factors for MSM effect in Ni49.7Mn29.1Ga21.2. No MSME can be observed below the temperature at which twinning stress (circles) exceeds the maximum possible magnetic stress K1=e0 (triangles). Transformation to austenite at 315K imposes the ultimate high temperature limit above which no MSME can occur. L. Straka, Dissertation, TKK, 2007. O.Heczko and L. Straka, Temperature dependence and temperature limits of magnetic shape memory effect, J. Appl. Phys., 94, No. 12, 2003, 7139-7143 .

Magn. anisotropy constant K1 and saturationmagnetization Ms as a function of temperature for Ni49.7Mn29.1Ga21.2. L. Straka and O. Heczko, Magnetic anisotropy in Ni-Mn-Ga martensites, J. Appl. Phys. 92, (2003) 8636-8639.

Magnetic properties cont.Type II magnetic contrast in alloy Ni48.9Mn30.8Ga20.3 (5M) in the TEM BEI (the magnetization direction is marked with black and white arrows). (a) Two-variant structure with the c-axis in the plane for both variants. (b) A nearly single-variant structure with the stripe magnetic domain pattern. The major variant has the c-axis in the plane and the minor variant has the c-axis out of the plane (the a- and c-axes of the major variant and the preceding compression direction σ are shown in the figure). Y. Ge, O. Heczko, O Söderberg, S-P Hannula and V K Lindroos, Smart Mat. And Struct. 14(2005), p. S212.

The magnetization curves (a) of 7M alloy measured in the crystallographic a-, b-and c-directions and (b) NM alloy measured in thecrystallographic a- and c-directions. Y. Ge et al.

Ni50.5Mn29.4Ga20.1 (7M) Ni52.8Mn25.7Ga21.5 (NM)

Actuation as a function of stress

(a)

(b)

Zero magnetic field

(c)Fig. a: Cyclic twinning stress measurement in H=0 at 35 °C for Ni47.6Mn30.5Ga22.9. Fig. b: Temperature dependency of cyclic twinning stressand respective strain amplitude. I. Aaltio, J. Tellinen, K. Ullakko and S.-P. Hannula, Proc. ACTUATOR 2006, pp. 402-405.

Fatigue properties of Ni-Mn-Ga

P. Müllner, Fracture under cyclic actuation (14M)ESOMAT2006 Bochum

Müllner et al.Journal of Applied Physics95 (2004) 1531-1536.

Magnetomechanical fatigue tests at TKK

• Electromagnetic test actuator underconstruction

• 10M (5M) Ni-Mn-Ga• Magnetic field flips appr. 90°• Pre-stress spring construction• Temperature of environment

stabilized• Freq. range appr. DC to 250 Hz• Strain level: 1 to 3.5 % variation

Power amplifier

Function generator

MSM-sample

DAQ-system

Displacementsensor

Vibration damping properties

Tan δ, storage modulus E’ and loss modulus E’’ as a function of temperature for (a) 10M type Ni49.7Mn29.1Ga21.2. and (b) NM type Ni55.1Mn22.1Ga22.9. I. Aaltio, M. Lahelin, O. Söderberg, O. Heczko, B. Löfgren, Y. Ge, J. Seppälä, S.-P. Hannula, Mat.Sci. and Eng. A, 2007, in press.

(a) (b)

MSM research projects at TKK Lab. of Material Science

• Demsmac II (2007-2009),Vibration damping properties of MSM-polymer composite materials, Partners: Tekes, Metso Paper, Adaptamat, Outotec, TKK, UCLA (Prof. Carman) (USA)

• MAFESMA Material algorithms, Finite Element methods, Experiments, (2007-2008/09), EU S3T project, • In Finland: Supported by Academy of Finland (FINMAFESMA and FORMAFESMA).

Partners in Finland:VTT, Oulu University. In Europe: KULeuven, Belgium (Prof. J. van Humbeeck), Academy of Sciences, Czech Republic, IOP (Dr. V. Novák, Dr. P. Sittner, Dr. M. Landa), University of Franche-Comte, France, (Prof. E. Patoor), UHP-ESSTIN, LEMTA, Vandoeuvre les Nancy, France, (Prof. T. Ben Zineb), Laboratoire de Mécanique Appliquée FEMTO-ST, France (Prof. C. Lexcellent),LMSN ENSIETA, France (Dr. S. Calloch)

• MULTIFUNC-NMG Effect of high anisotropic thermal expansion on structure in the Ni-Mn-Ga-(X) single crystals possessing multifunctional properties (2007-2008), EU INTAS projectInstitute for Metal Physics, Kiev, Ukraine (Dr. N. Glavatska), Ruhr-University, Bochum, Germany (Prof. G. Eggeler), Institute Laue-Langevin, Grenoble, France (Prof. J. Rodriguez-Carvajal)

• Researcher visit programs (Academy of Finland), Institue for Metal Physics (Kiev, Ukraina)Academy of Sciences,Institute of Physics (Prague, Czech republic)Slovak Academy of Sciece (Slovakia)

Present challenges of MSM researchNow:• Control of the properties of Ni-Mn-Ga MSM

materials, and obtaining scientific research resultsabout it.

• Fatigue properties• Vibration damping properties

In the future: • Increase of the operating temperature range• Production (industry)• Industrial use and related new challenges

Picture: Picture: CrystallizationCrystallization furnacefurnace (TKK)(TKK)

International aspect of MSM research

• Initiation: Discovery of the MSM-effect in 1995 at TKK, patent applicationand first publication at MIT in 1996.

• Year 2007: more than 730 published articles and active MSM researchgroups around the world.

FlagsFlags representrepresent the the groupsgroups thatthat havehave publishedpublished workwork of MSM.of MSM.