Magnetic Shape Memory Alloys

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1 Sebastian Fähler and Kathrin Dörr, IFW Dresden Magnetic Shape Memory Alloys Magnetically Induced Martensite (MIM) Magnetically Induced Reorientation (MIR) Requirements for actuation Exotic materials German Priority Program SPP 1239: Modification of Microstructure and Shape of solid Materials by an external magnetic Field

2 Multiferroics magnetoelectric effect magnetic shape memory effect 2

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

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

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

6 6 7M Martensite

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

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

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

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

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

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

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

14 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 atoms simultaneously... 14

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

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

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

18 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) TB 18 0 mt 200 mt H Magnetic field moves twin boundary instead of magnetization rotation

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

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

21 Sebastian Fähler and Kathrin Dörr, IFW Dresden Magnetic Shape Memory Alloys Magnetically Induced Martensite (MIM) Magnetically Induced Reorientation (MIR) Requirements for actuation Exotic materials German Priority Program SPP 1239: Modification of Microstructure and Shape of solid Materials by an external magnetic Field

22 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 ε =1 c 0 a Extrinsic properties (microstructure, texture) High strain ε < ε 0 Low switching field H S < H A Easily moveable twin boundaries rubber like behavior Aim: high strain in low magnetic fields Beneficial conditions for MIR 22

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

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

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

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

27 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) 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

28 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 28 H. H. Liebermann, C. D. Graham, Acta Met. 25 (7) (1977) 715

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

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

31 Magnetically Induced Martensite (MIM) Essential Martensitic transformation with large J Low Hysteresis Low S Transformation around RT Magnetocrystalline anisotropy Magnetic Shape Memory Alloys Beneficial Not needed Magnetically Induced Reorientation (MIR) Magnetocrystalline anisotropy Easily movable twin boundaries Ferromagnetism (High J S ) Martensitic transformation (rubber like behavior) Magnetostriction 31

32 32

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

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

35 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 35

Influence of Magnetic Field Intensity on the Temperature Dependence of Magnetization of Ni 2.08 Mn 0.96 Ga 0.96 Alloy

J. Electromagnetic Analysis & Applications, 2010, 2, 431-435 doi:10.4236/jemaa.2010.27056 Published Online July 2010 (http://www.scirp.org/journal/jemaa) 431 Influence of Magnetic Field Intensity on the