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Sebastian Fhler and Kathrin Drr, IFW Dresden Magnetic Shape Memory Alloys Magnetically Induced Martensite (MIM) Magnetically Induced Reorientation (MIR) Requirements for actuation Exotic materials

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Sebastian Fähler and Kathrin Dörr, IFW Dresden

Magnetic Shape Memory Alloys

  • Magnetically Induced

Martensite (MIM)

  • Magnetically Induced

Reorientation (MIR)

  • Requirements for actuation
  • “Exotic” materials

www.adaptamat.com

German Priority Program SPP 1239: “Modification of Microstructure and Shape of solid Materials by an external magnetic Field” www.MagneticShape.de

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Multiferroics

magnetoelectric effect magnetic shape memory effect

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Single ion effect (spin-orbit

coupling) – no collective phenomenon

Anisotropic magnetostriction

  • Strain < 0.24 %

+ High frequency + Low magnetic field

Not important for Magnetic Shape Memory Alloys

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Martensitic transformation

T > TM: Austenite (high symmetry) T < TM : Martensite (low symmetry)

No diffusion, reversible Twinned microstructure of martensite Thermal actuation

⇒ conventional shape memory effect

+ Strain > 5% + High forces

  • Low frequency
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Prototype Ni-Mn-Ga, Shearing

Ni2+xMn1-xGa L21

(110)

bcc - sheared Why are structures instable? → Phonon spectra

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7M Martensite

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Martensitic transformation of magnets

Modification of structure and

shape by a magnetic field

  • High magnetic field

>> 1 T

  • Narrow temperature

regime

  • A. N. Vasil'ev, V. D.

Buchel'nikov, T. Takagi, V. V. Khovailok, E. I. Estrin, Physics Uspekhi 46(6) (2003) 559-588

Ni2.15Mn0.81Fe0.04Ga

M a r t e n s i t e a n d A u s t e n i t e Non-magnetic Austenite Ferromagnetic Martensite ~ 1 K/T

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Martensitic transformation of magnets

Modification of structure and

shape by a magnetic field

  • High magnetic field

>> 1 T

  • Narrow temperature

regime

  • A. N. Vasil'ev, V. D.

Buchel'nikov, T. Takagi, V. V. Khovailok, E. I. Estrin, Physics Uspekhi 46(6) (2003) 559-588

Ni2.15Mn0.81Fe0.04Ga

M a r t e n s i t e a n d A u s t e n i t e Non-magnetic Austenite Ferromagnetic Martensite ~ 1 K/T

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Magnetically Induced Martensite (MIM)

Magnetic actuation Latent heat (magnetocaloric effect):

here a problem

+ Remote actuation

Magnetic field favors ferromagnetic phase Clausius Clapeyron:

S J dH dT ∆ ∆ =

∆J: magn. polarization difference in martensite and austenite state ∆S: entropy difference

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New Materials: Inverse Transformation

Magnetic field favors high temperature austenite because its ferromagnetism is stronger than that of martensite

Shift of MS by -8 K/T Large magnetocaloric effect

Magnetically weaker Martensite Magnetically stronger Austenite

DSC: Ni-Mn-In

  • T. Krenke, M. Acet, E.
  • F. Wassermann, X.

Moya, L. Manosa, A. Planes, Phys. Rev. B 73 (17) (2006) 174413

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Magnetically Induced Austenite (MIA)

Negative ∆ J → H stabilizes austenite Magnetic field favors ferromagnetic phase Clausius Clapeyron:

S J dH dT ∆ ∆ =

∆J: magn. polarization difference in martensite and austenite state ∆S: entropy difference

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Magnetically Induced Austenite (MIA)

Hysteresis may inhibit

reversibility !

+ Strain ~ 3% Hysteresis losses? + No anisotropy needed

  • R. Kainuma et al.

Nature 439 (2006) 957

Ni45Co5Mn36.7In13.3

FM Austenite NM Martensite

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13 2 4 6 8 10 12 1 2 3 HMI Berlin

Applied Strain in %

HUT Finnland

Recorded Stress in MPa

Rubber like behavior

Easy movement of twin boundaries

(~ MPa)

Ni-Mn-Ga, 7M

At const T < TM

  • Little pinning of twin

boundaries at defects

F

  • R. Schneider, HMI Berlin
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Twin boundary movement Twin boudary

Only highly symmetric twin boundaries are highly mobile But a collective movement would require to move 1023

atoms simultaneously...

A3: P. Entel,

  • U. Duisburg-Essen
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Microscopic view of twin boundary movement

Dislocation (step + screw) as

elemental step of twin boundary movement

  • P. Müllner et al., JMMM 267

(2003) 325

„Intrinsic“ Peierls stress to

move Burgers vector ~ 10-13 Pa

  • S. Rajasekhara, P. J. Ferreira

Scripta Mat. 53 (2005) 817

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Magnetically Induced Reorientation (MIR)

Twin boundary movement No phase transition, affects only microstructure Requires:

Non-cubic phase High magnetocrystalline aniosotropy Easily movable twin boundary

++ Strain ≤ 10 % ! + High frequency

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Ferromagnet

Rotation of magnetization must be avoided

⇒ high magnetocrystalline anisotropy needed

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Domain and twin boundary dynamics

0 mT 200 mT

H

Magnetic field moves twin boundary instead of

magnetization rotation

Y.W. Lai, N. Scheerbaum, D. Hinz, O. Gutfleisch, R. Schaefer, L. Schultz, J. McCord,

  • Appl. Phys. Lett. 90 (2007) 192504

TB

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Integral measurement of strain and magnetization

  • O. Heczko, L. Straka, N.

Lanska, K. Ullakko, J. Enkovaara, J. Appl. Phys. 91(10) (2002) 8228

H H 1 1 1 3 3 3 4 4 4 5 5 5 2 2 2

Ni-Mn-Ga 5M

  • moderate switching

field HS < 1 T

H

HS

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Setup of a linear actuator H=0 H1 H2 F F F F H=0 H3

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Sebastian Fähler and Kathrin Dörr, IFW Dresden

Magnetic Shape Memory Alloys

  • Magnetically Induced

Martensite (MIM)

  • Magnetically Induced

Reorientation (MIR)

  • Requirements for actuation
  • “Exotic” materials

www.adaptamat.com

German Priority Program SPP 1239: “Modification of Microstructure and Shape of solid Materials by an external magnetic Field” www.MagneticShape.de

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Intrinsic properties (composition, phase)

  • High martensitic transformation temperature ⇒ high application

temperature

  • High magnetocrystalline anisotropy ⇒ avoids rotation of

magnetization

  • High magnetization ⇒ high blocking stress
  • Large maximum strain

Extrinsic properties (microstructure, texture)

  • High strain
  • Low switching field HS< HA
  • Easily moveable twin boundaries ⇒ rubber like behavior

Aim: high strain in low magnetic fields

Beneficial conditions for MIR

a c − =1 ε ε ε <

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Martensitic transformation Ferromagnetism High uniaxial magnetocrystalline

anisotropy

High magnetostriction Chemical ordering

What is essential for the MSM effect?

Not fulfilled for: Tb, Dy, ReCu2 ReCu2, La2-xSrxCuO4 Fe70Pd30, Ni-Mn-In Ni-Mn-Ga Fe70Pd30, Tb, Dy

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Not appropriate to describe threshold like switching

(Reorientation or Martensitic transformation)

Anisotropic magnetostriction

Constrained 5M NiMnGa single crystals

λS = - 50 ppm

  • O. Heczko, J. Mag. Mag. Mat. 290-291

(2005) 846

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Fe70Pd30

Austenite: fcc Martensite: fct, c/a <1 two easy axis || a

R.D. James, M. Wuttig

  • Phil. Mag. 77 (1998) 1273

a a c

No uniaxial anisotropy needed No chemical ordering

  • J. Cui, T.W. Shield, R.D. James,

Acta Mat. 52 (2004) 35

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Tb0.5Dy0.5Cu2

  • S. Raasch, et al. PRB

73 (2006) 64402

no martensitic transformation

  • rthorhombic (pseudohexagonal,

3 variants)

1.5 % strain at 3.2 T by reorientation

H

Canted magnetic order

M ( µ

B

/ f . u . )

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La2-xSrxCuO4 (LSCO)

  • A. N. Lavrov, S.

Komiya, Y. Ando, Nature 418 (2002) 385

Orthorhombic, twinning in ab plane, b axis (red

domains) aligns parallel to magnetic field

Antiferromagntic, weak ferromagnetic moment

  • A. N. Lavrov, Y.

Ando, S. Komiya, I. Tsukada, Phys. Rev.

  • Lett. 87 (2001) 17007

H = 14 T RT 1% strain

1 mm

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Dy, Tb

  • J. J. Rhyne et al. J. Appl. Phys. 39(2) (1968) 892
  • S. Chikazumi et al. IEEE Trans. Mag.

MAG-5(3) (1969) 265

8% strain in Tb (40 T, 4K)

Pure elements

Dy single crystal at 4 K

  • H. H. Liebermann, C. D. Graham,

Acta Met. 25 (7) (1977) 715

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Ni-Mn-In

Magnetic field favors high temperature austenite because its ferromagnetism is stronger than that of martensite

No significant magnetocrystalline anisotropy

(cubic ferromagnet)

Magnetically weaker Martensite Magnetically stronger Austenite

DSC:

  • T. Krenke, M. Acet, E.
  • F. Wassermann, X.

Moya, L. Manosa, A. Planes, Phys. Rev. B 73 (17) (2006) 174413 H = 50 kOe

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Magnetic Shape Memory Alloys Martensite (SMA) Ferromagnet FMSMA Magnetic Ordering MSMA MIR MIM

NiMnGa NiMnIn FePd Fe3Pt Tb Dy CoNiGa ReCu2 FeNiGa La2-xSrxCuO4

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Magnetic Shape Memory Alloys

Magnetically Induced Martensite (MIM)

Martensitic transformation with large ∆J Low Hysteresis Low ∆S Transformation around RT Magnetocrystalline anisotropy

Magnetically Induced Reorientation (MIR)

Magnetocrystalline anisotropy Easily movable twin boundaries Ferromagnetism (High JS) Martensitic transformation (rubber like behavior) Magnetostriction

Essential Beneficial Not needed

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Martensitic and Ferromagnetic

Magnetic domains Crystallographic variants Short axis aligned by stress Magnetization direction aligned by field

H F F

Coupled by magneto- Crystalline anisotropy

H Domain and variant movement

→ local mechanism

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Martensitic and Ferromagnetic

Magnetic domains Crystallographic variants Short axis aligned by stress Magnetization direction aligned by field

H F F

Coupled by magneto- crystalline anisotropy

H

50 µm

Twin boundaries (Variant boundaries, grain boundaries) 90°and 180° Domain boundaries

B1: J. McCord,

  • R. Schäfer,

IFW Dresden

Kerr microscopy:

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Magnetic Shape Memory Alloys

Magnetically Induced Martensite (MIM) + Little constrains on microstructure + No magnetocrystalline anisotropy needed Forces?

  • High fields > 1 T
  • Works only at the vicinity of

martensitic transformation

  • Magnetocaloric effect inhibits high

frequency Magnetically Induced Reorientation (MIR)

  • Rubber like behavior needed
  • High magnetocrystalline

anisotropy

  • Low forces

+ Moderate fields < 1 T + Works below martensitic transformation + High frequency (kHz) possible