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Departament d’Estructura i Constituents de la Matèria Universitat de Barcelona

Structure and magnetism in the premartensitic and martensitic states in Heusler shape-memory alloys. Antoni Planes. Departament d’Estructura i Constituents de la Matèria Universitat de Barcelona.

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Departament d’Estructura i Constituents de la Matèria Universitat de Barcelona

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  1. Structure and magnetism in the premartensitic and martensitic states in Heusler shape-memory alloys Antoni Planes Departament d’Estructura i Constituents de la Matèria Universitat de Barcelona Collaborators:E. Bonnot, T. Castán, Ll. Mañosa, X. Moya, M. Porta, E. Vives (UB), A. Saxena, T. Lookman, J. Lashley (Los Alamos), M. Acet, T. Krenke, E.F. Wassermann, S. Aksoy (Duisburg), M. Morin (INSA). T.A. Lograsso, J.L. Zarestky (Ames) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  2. Introduction Magnetic shape-memory effect refers to the change of shape (deformation) of a magnetic material undergoing a martensitic transition caused by either:  inducing the transition or  rearranging the martensitic variants by means of an applied magnetic field Prototypical shape-memory alloy: Ni-Mn-Ga Maximum induced deformation ~ 10% with an applied field ~ 10 kOe  two orders of magnitude larger than in magnetosrictive Terfenol-D (Tb0.27Dy0.73Fe2) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  3. Shape-memory properties Superelastic Elastic Elastic Shape-memory effect Superelasticity Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  4. Magnetic shape-memory properties Superelastic H Elastic Elastic H Magnetic shape-memory effect Magnetic superelasticity Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  5. Magnetic shape-memory materials HEUSLER Ni-Mn-X Ullakko et al., APL, 69, 1966 (1996) (Ga) (X= Ga, Al, In, Sn, …) Fujita et al., APL, 77, 3054 (2000) (Al) Sutou et al., APL, 85, 4358 (2004); Krenke et al., PRB, 72, 014412 (2005); 73, 174413 (2006) (In,Sn) Co-Ni-Al Oikawa et al., APL, 79, 2472 (2001) Ni-Fe-Ga Morito et al., APL, 81, 5201 (2002); 83, 4993 (2003) IRON-BASED Fe-Pd James & Wuttig, PMA, 77, 1273 (1998) Fe-Pt Kakeshita et al., APL, 77, 1502, (2000) Co-Ni Zhou et al., APL, 82, 760 (2003) La2-xSrxCuO4 Lavrov et al., Nature, 418, 385 (2002) (antiferro) OTHER Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  6. Microscopic scale Mesoscopic scale Elastic domains (variants) (spin-phonon interplay) Magnetic domains Magnetostructural interplay Interplay Structural degrees of freedom Magnetic degrees of freedom Unique pretransitional behaviour Magnetic shape-memory Magnetic superelasticity Magnetocaloric effect Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  7. Outline • Phase diagram and general properties • Pretransitional effects: Phonon anomalies and the intermediate transition  Conclusions Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  8. Magnetic properties Ni Ni2MnGa Mn Heusler, L21 (Fm3m) Ga • Ferromagnetic order (Tc~ 370 K) • Total magnetic moment: µtotal 4.1 µBper f.u. Non-stoichiometric Ni2Mn1+xGa1-x (µNi 0.3 µBper f.u.) • Weak magnetic anisotropy Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  9. Phase diagram Phase diagram at constant Ga concentration L21-para L21-ferro Intermediate Ni2+xMn1-xGa Martensite From: Vasil’ev et al., Physics-Uspekhi, 46, 559 (2003) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  10. Phase diagram Relative phase stability controlled (to a large extent) by the average number of valence electrons per atom, e/a Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  11. Other effects From: Khan et al., J. Phys. Condens. Matter, 16, 5259 (2004) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  12. Martensitic transition mechanism 10M ([32]2) Cubic 14M ([52]) Transformation mechanism: Shear + Shuffle on {110} planes along <1-10> directions Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  13. 10M 14M NM (L10 ) Martensitic structure By increasing e/a the following structures occur: From: Lanska et al., J. Appl. Phys., 95, 8074 (2004) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  14. Entropy change Ni-Mn-Ga Ni-Mn-In Ni-Mn-Sn ferro para ferro para ferro para Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  15. e/a Magnetic properties From: Enkovaara et al., PRB, 67, 212405 (2003). From: Albertini et al., APL, 81, 4032 (2002). Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  16. Ni50Mn35Sn15 Ni50Mn34In16 Ni56.2Mn18.2Ga25.5 Ni49.5Mn24.5Ga25.1 Effect of a magnetic field ΔS independent of H Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  17. Precursors in phase transitions • Nanoscale structures which occur above phase transitions. They announce that a system is preparing for the phase transition before it actually takes place. • Often observed in ferroic and multiferroic materials. • Revealed by high-resolution imaging techniques well above the (expected) phase transition. • Detected as anomalies in diffraction experiments (intense diffuse scattering) and in the response to certain exitations. • Not expected in systems undergoing first-order transions (which are expected to occur abruptly). • In martensites, related to low restoring forces in specific lattice directions (transition path). Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  18. Example: tweed Structural precursors in Ni-Al (similar phenomenology in Fe-Pd, ….., shape-memory alloys) TEM Neutron Diffraction Cross-hatched striations (tweed) parallel to {110} planes observed above TM. (020) (60 nm) From, S.M. Shapiro et al., PRL, 57, 3199 (1986) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  19. Phonons in Ni-Mn-Ga Acoustic-phonon dispersion curves for the cubic phase of Ni2MnGa. From: Zheludev et al., 54, 15045 (1996). L21 5M L21 7M TA2 branch at selected temperatures. The position of the dip depends on the selected martensite structure. From: Mañosa et al. PRB, 64, 024305 (2001) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  20. Phonon softening L21→ 5M (low e/a) TM TI (higher e/a) Slopes in the two phases Ni-Al(from Shapiro et al., PRL, 62, 1298 (1989); PRB, 44, 9301 (1991) • The softening is enhanced at the Curie point. • For systems transforming to the 5M structure, the softening is nearly complete at TI > TM. Upon further cooling the frequency increases. • At TI the system undergoes the intermediate transition. Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  21. Elastic constants L21 7M L21 5M Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  22. Diffraction experiments (111) T > TI (100) T < TI T < TI TEM J. Pons, private communication Elastic scattering along the (ξξ0) direction The transition at TI is associated with the lock-in of the pseudoperiodic tweed phase into a commensurate phase due to the freezing of the anomalous phonon. Neutrons Modulation of {110} planes with wave number 1/3 along <1-10> direction. Preserve cubic symmetry. From A. Zheludev et al., PRB, 54, 15045 (1996) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  23. Magnetic and thermal anomalies Further results which prove the existance of the premartensitic transition. A.c. magnetic susceptibility Calorimetry TI Latent heat= 9 J/mol (Martensitic transition:~ 100 J/mol) The intermediate transition is first-order A. Planes et al., PRL 79, 3926 (1997) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  24. Effect of external fields Transition temperatures: Elastic constant [1-10] direction [001] direction STRESS [1-10] direction 4.5 MPa 0 MPa 1 MPa From: Gozàlez-Comas et al., PRB , 60, 7085 (1999) MAGNETIC FIELD TI~ M2 From: W.H. Wang et al., J. Phys. Condens. Matter, 13, 2607 (2001) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  25. Comparison with non-magnetic SMA High temperature phase (cubic) Ttw ? Tweed TI Modulated (or intermediate) phase TM Martensite Ni-Mn-Ga Ni-Al Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  26. Landau model Amplitude of the relevant phonon mode Order parameters: MagnetizationM Free energy: Expansions: Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  27. Landau model • Minimization with respect to Mgivesthe following effective free-energy: • where: • M0is the magnetization of the high temperature phase ( = 0): Tcis the Curie temperature Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  28. Landau model: results • • If 12/Bis large, can be negative, and a first-order transition is possible. The transition temperature is: • The temperature dependence of the anomalous phonon frequency: • 1 > 0 softening is enhanced. • Clausius-Clapeyron equation: • Results in agreement with the experiments if1 > 0 Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  29. When an intermediate transition occurs? Results for Ni-Mn-Ga(Fe) Tc Ms Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  30. Conclusions In Heusler alloys the relative phase stability is (to a large extent)controlled by e/a. Compared to other shape-memory alloys, Ni-Mn-Ga shows unique pretransitional behaviour which is a consequence of spin-phonon coupling. Strong softening of the 1/3[110]TA2 phonon and large magnetisation is required for a first-order intermediate transition to occur. The intermediate phase almost preserves cubic symmetry and results from the freezing of 1/3[110]TA2 phonon. Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  31. Magnetic shape-memory effect • Transition at zero-field: Formation of twin related variant. • The magnetic easy axis changes from one twin to the other Cubic → Martensite (twinned) Twin related variants and magnetic stripe domains inside From: Ge et al., JAP, 96, 2159 (2004). • Effect of a magnetic field Weak anisitropy Strong anisitropy In systems with strong anisotropy and highly mobile boundaries, field induced rearrangement of martensitic variants is possible  Magnetic Shape-Memory Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  32. Example Field induced deformation in a Ni-Mn-Ga alloy From: Likhachev et al., Proc SPIE, 4333, 197 (2001) • The residual deformation remaining when the field is removed can be removed by: • Heating up through the transition • Application of a magnetic field perpendicular to the original • Application of a stress that opposes the applied field Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  33. Magnetic superelasticity Magnetic superelasticity in Ni-Mn-In alloy From: Krenke et al., PRB, (2007) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  34. Magnetocaloric effect Adiabatic Temperature change, Tadi Isothermal Entropy change, Siso when a magnetic field H is applied/removed It is given by: ∆Te is the range over which the transition extends. Controlled by the change of magnetization at the transition ΔM= MM – MP > 0, Conventional magnetocaloric effect ΔM= MM – MP < 0, Inverse magnetocaloric effect Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  35. Magnetocaloric effect in Ni2MnGa Ni49.5Mn25.4Ga25.1 ∆M = MM - MP Inverse magnetocaloric effect Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  36. Physical picture Cubic Tetragonal (a) (b) (c) Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

  37. Historical • Magnetostructural characterization, Ziebeck’s group [Philos.Mag. B, 49, 295 (1984)] • Martensitic Transformation and Shape-Memory Properties (Martynov, Kokorin, …) • Phonon anom. & Intermediate trans., Shapiro’s group PRB, 51, 11310 (1995) • Magnetic Shape-Memory Effect, O´Handley’s group at MIT, APL, 69, 1966 (1996) • Magnetoelastic coupling. Vordervisch, Trivisono, UB group (phonons/elas. cnts, 1997) • Modelling: O’Handley (JAP, 1998), James & Wuttig (PMB, 1998), ….. • First.Principles Calculations: Helsinski group, Duisburg group, … • Further developments, MIT group, Helsinki group, ….. • Development of other M-SMA: Ishida’s group, Kakeshita’s group, …. • Magnetic superelasticity: Duisburg & Barcelona, PRB, 2007 Fundamentals of the Magnetic Shape-Memory Effect: Material properties and atomistic simulations, Ringberg Castle (Germany), February 14-16, 2007

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