Magnetic Shape Memory Alloys Magnetically Induced Martensite - PowerPoint PPT Presentation

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

Multiferroics magnetoelectric effect magnetic shape memory effect 2

Anisotropic magnetostriction Not important for Magnetic Shape Memory Alloys - Strain < 0.24 % � Single ion effect (spin-orbit + High frequency coupling) – no collective + Low magnetic field phenomenon 3

Martensitic transformation T > T M : Austenite (high symmetry) T < T M : Martensite (low symmetry) � No diffusion, reversible � Twinned microstructure of martensite + Strain > 5% � Thermal actuation + High forces - Low frequency ⇒ conventional shape memory effect 4

Prototype Ni-Mn-Ga, Shearing (110) Ni 2+x Mn 1-x Ga L2 1 bcc - sheared Why are structures instable? → Phonon spectra 5

7M Martensite 6

Martensitic transformation of magnets Ni 2.15 Mn 0.81 Fe 0.04 Ga ~ 1 K/T A. N. Vasil'ev, V. D. Buchel'nikov, T. Takagi, V. V. Khovailok, E. I. Estrin, Ferromagnetic Physics Uspekhi 46(6) d (2003) 559-588 n Martensite a e e t i t s i n n e e t t s r a u M A Non-magnetic Austenite � Modification of structure and - High magnetic field >> 1 T shape by a magnetic field - Narrow temperature regime 7

Martensitic transformation of magnets Ni 2.15 Mn 0.81 Fe 0.04 Ga ~ 1 K/T A. N. Vasil'ev, V. D. Buchel'nikov, T. Takagi, V. V. Khovailok, E. I. Estrin, Ferromagnetic Physics Uspekhi 46(6) d (2003) 559-588 n Martensite a e e t i t s i n n e e t t s r a u M A Non-magnetic Austenite � Modification of structure and - High magnetic field >> 1 T shape by a magnetic field - Narrow temperature regime 8

Magnetically Induced Martensite (MIM) Magnetic field favors ferromagnetic phase Clausius Clapeyron: ∆ = dT J ∆ dH S ∆ J: magn. polarization difference in martensite and austenite state ∆ S: entropy difference � Magnetic actuation + Remote actuation � Latent heat (magnetocaloric effect): here a problem 9

New Materials: Inverse Transformation Ni-Mn-In Magnetic field favors high temperature austenite because its ferromagnetism is stronger than that of martensite Magnetically weaker DSC: Martensite Magnetically stronger Austenite T. Krenke, M. Acet, E. F. Wassermann, X. � Shift of M S by -8 K/T Moya, L. Manosa, A. Planes, Phys. Rev. B � Large magnetocaloric effect 73 (17) (2006) 174413 10

Magnetically Induced Austenite (MIA) Magnetic field favors ferromagnetic phase Clausius Clapeyron: ∆ = dT J ∆ dH S ∆ J: magn. polarization difference in martensite and austenite state ∆ S: entropy difference Negative ∆ J → H stabilizes austenite 11

Magnetically Induced Austenite (MIA) Ni 45 Co 5 Mn 36.7 In 13.3 FM Austenite R. Kainuma et al. Nature 439 (2006) 957 NM Martensite + Strain ~ 3% � Hysteresis may inhibit Hysteresis losses? reversibility ! + No anisotropy needed 12

Rubber like behavior Ni-Mn-Ga, 7M At const T < T M F 3 Recorded Stress in MPa 2 HUT Finnland 1 HMI Berlin R. Schneider, HMI Berlin 0 0 2 4 6 8 10 12 Applied Strain in % - Little pinning of twin � Easy movement of twin boundaries boundaries at defects (~ MPa) 13

Twin boundary movement A3: P. Entel, U. Duisburg-Essen Twin boudary � Only highly symmetric twin boundaries are highly mobile � But a collective movement would require to move 10 23 atoms simultaneously... 14

Microscopic view of twin boundary movement � Dislocation (step + screw) as P. Müllner et al., JMMM 267 elemental step of twin boundary (2003) 325 movement � „Intrinsic“ Peierls stress to S. Rajasekhara, P. J. Ferreira move Burgers vector ~ 10 -13 Pa Scripta Mat. 53 (2005) 817 15

Magnetically Induced Reorientation (MIR) Twin boundary movement No phase transition, affects only microstructure Requires: � Non-cubic phase ++ Strain ≤ 10 % ! � High magnetocrystalline aniosotropy + High frequency � Easily movable twin boundary 16

Ferromagnet � Rotation of magnetization must be avoided ⇒ high magnetocrystalline anisotropy needed 17

Domain and twin boundary dynamics Y.W. Lai, N. Scheerbaum, D. Hinz, O. Gutfleisch, R. Schaefer, L. Schultz, J. McCord, Appl. Phys. Lett. 90 (2007) 192504 TB 200 mT 0 mT H � Magnetic field moves twin boundary instead of magnetization rotation 18

Integral measurement of strain and magnetization Ni-Mn-Ga 4 5 3 5M H H 3 4 2 2 1 5 H S O. Heczko, L. Straka, N. Lanska, K. Ullakko, J. 3 4 5 1 Enkovaara, J. Appl. Phys. 91 (10) (2002) 8228 2 1 H o moderate switching field H S < 1 T 19

Setup of a linear actuator F F H 1 H=0 H 2 H 3 H=0 F F 20

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

Beneficial conditions for MIR Intrinsic properties (composition, phase) • High martensitic transformation temperature ⇒ high application temperature • High magnetocrystalline anisotropy ⇒ avoids rotation of magnetization • High magnetization ⇒ high blocking stress ε = 1 − • Large maximum strain c 0 a Extrinsic properties (microstructure, texture) ε < ε • High strain 0 • Low switching field H S < H A • Easily moveable twin boundaries ⇒ rubber like behavior Aim: high strain in low magnetic fields 22

What is essential for the MSM effect? Not fulfilled for: � Martensitic transformation Tb, Dy, Re Cu 2 � Ferromagnetism Re Cu 2 , La 2-x Sr x CuO 4 � High uniaxial magnetocrystalline Fe 70 Pd 30, Ni-Mn-In anisotropy � High magnetostriction Ni-Mn-Ga � Chemical ordering Fe 70 Pd 30 , Tb, Dy 23

Anisotropic magnetostriction Constrained 5M NiMnGa single crystals λ S = - 50 ppm O. Heczko, J. Mag. Mag. Mat. 290-291 (2005) 846 � Not appropriate to describe threshold like switching (Reorientation or Martensitic transformation) 24

Fe 70 Pd 30 Austenite: fcc Martensite: fct, c/a <1 two easy axis || a c a a R.D. James, M. Wuttig J. Cui, T.W. Shield, R.D. James, Phil. Mag. 77 (1998) 1273 Acta Mat. 52 (2004) 35 � No uni axial anisotropy needed � No chemical ordering 25

Tb 0.5 Dy 0.5 Cu 2 S. Raasch, et al. PRB H 73 (2006) 64402 � no martensitic transformation � orthorhombic (pseudohexagonal, 3 variants) ) . u . f / B µ ( M � Canted magnetic order � 1.5 % strain at 3.2 T by reorientation 26

La 2-x Sr x CuO 4 (LSCO) A. N. Lavrov, S. Komiya, Y. Ando, Nature 418 (2002) 385 A. N. Lavrov, Y. Ando, S. Komiya, I. Tsukada, Phys. Rev. Lett. 87 (2001) 17007 H = 14 T RT 1% strain 1 mm � Orthorhombic, twinning in ab plane, b axis (red domains) aligns parallel to magnetic field � Antiferromagntic , weak ferromagnetic moment 27

Dy, Tb Dy single crystal at 4 K 8% strain in Tb (40 T, 4K) S. Chikazumi et al. IEEE Trans. Mag. MAG-5(3) (1969) 265 J. J. Rhyne et al. J. Appl. Phys. 39 (2) (1968) 892 � Pure elements H. H. Liebermann, C. D. Graham, Acta Met. 25 (7) (1977) 715 28

Ni-Mn-In Magnetic field favors high temperature austenite because its ferromagnetism is stronger than that of martensite Magnetically weaker H = 50 kOe DSC: Martensite Magnetically stronger Austenite � No significant magnetocrystalline anisotropy T. Krenke, M. Acet, E. (cubic ferromagnet) F. Wassermann, X. Moya, L. Manosa, A. Planes, Phys. Rev. B 29 73 (17) (2006) 174413

Magnetic Shape Memory Alloys NiMnGa FePd Fe 3 Pt Dy Tb La 2-x Sr x CuO 4 Re Cu 2 MIR Magnetic Martensite MSMA Ferromagnet FMSMA Ordering (SMA) MIM NiMnIn FeNiGa CoNiGa 30

Magnetic Shape Memory Alloys M agnetically I nduced M artensite M agnetically I nduced (MIM) R eorientation (MIR) Essential Martensitic transformation with Magnetocrystalline anisotropy large ∆ J Easily movable twin boundaries Beneficial Low Hysteresis Ferromagnetism (High J S ) Low ∆ S Martensitic transformation Transformation around RT (rubber like behavior) Not needed Magnetocrystalline anisotropy Magnetostriction 31

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Martensitic and Ferromagnetic Magnetic domains Crystallographic variants Coupled by magneto- Crystalline anisotropy H H F F Short axis aligned by stress Magnetization direction aligned by field Domain and variant movement → local mechanism 33

Martensitic and Ferromagnetic Crystallographic variants Coupled by magneto- Magnetic domains crystalline anisotropy H H F F Short axis aligned by stress Magnetization direction aligned by field Kerr microscopy: B1: J. McCord, R. Schäfer, 50 µm IFW Dresden Twin boundaries 90°and 180° (Variant boundaries, Domain boundaries grain boundaries) 34