MSMnet: Magnetomechanics of Magnetic Shape Memory Alloys: Session 3
Program Organizers: Peter Müllner, Boise State University

Tuesday 4:00 PM
July 11, 2017
Room: Wrigley
Location: Hyatt Regency Chicago

Session Chair: Ibrahim Karaman, Texas A&M University

4:00 PM  
Multicaloric Effects in Metamagnetic Heusler Shape-memory Alloys: Avadh Saxena1; Teresa Castan2; Lluis Manosa2; Enric Stern-Taulats2; Antoni Planes2; 1Los Alamos National Laboratory; 2University of Barcelona
    Metamagnetic shape-memory alloys display cross-response to both magnetic and mechanical (e.g. hydrostatic pressure and uniaxial stress) fields, and thus they are good candidates to support multicaloric effects induced by simultaneous or sequential application of such fields. The interest in multicaloric effects is two-fold. On the one hand, it is expected that the provision of operating with more than one field should provide the possibility of controllably enhancing the caloric response and improving its reproducibility with cycling, and, on the other, of selecting the optimal temperature working range. We will show that multicaloric effects comprise the contributions from the effects associated with each relevant ferroic property together with the cross-contribution arising from its interplay. This will be illustrated with examples for a number of metamagnetic Heusler shape-memory alloys. Results will be analysed within the framework of a Landau model with appropriate coupling between the corresponding structural and magnetic order parameters.

4:20 PM  
Composition Dependence of the Multi-ferroic Transformation in Ni-Co-Mn-In Metamagnetic Shape Memory Alloys: Daniel Salas Mula1; Olga Eliseeva1; Nickolaus Bruno1; Igor Roshchin1; Ruben Santamarta2; Raymundo Arroyave1; Thien Duong1; Ibrahim Karaman1; 1Texas A&M University; 2Universitat de les Illes Balears
     Ni-Co-Mn-In Meta-Magnetic Shape Memory Alloys (MMSMAs) undergo a martensitic transformation (ferroelastic transition) which is coupled with a strong decrease in the magnetic ordering from a ferromagnetic parent phase to a weak-magnetic product phase (ferromagnetic transition). The properties of this multi-ferroic transformation (MFT) have been shown to present a strong dependence on its microstructure and thus can be tuned through small changes in composition and thermal treatments. MMSMAs can present ferroelastic glass (strain-glass) and ferromagnetic glass (cluster spin-glass) transitions becoming prominent active materials.The goal of the present work is to understand the dependence of the MFT properties and the onset of the arrest phenomena on composition, In content, and different microstructural elements, degree of atomic ordering and crystalline defects. Results arise a complex relationship between MFT properties and material’s microstructure originated by the existence of different competitive contributions to the phase stability and local strain distortions.

4:55 PM  
Thermoelastic Characterization of Thin Epitaxial Ni-Mn-Ga Films by Impulsive Stimulated Thermal Scattering: Pavla Stoklasova1; Petr Sedlak1; Hanus Seiner1; Sebastian Faehler2; Jan Sermeus3; Christ Glorieux3; Anja Backen2; Oleg Heczko4; Michal Landa1; 1Institute of Thermomechanics, CAS; 2IFW Dresden; 3KU Leuven; 4Institute of Physics, CAS
    We studied temperature evolution of elastic and thermal properties of austenite and martensite states of epitaxial Ni-Mn-Ga films on a MgO substrate. An all-optical technique - Impulsive Stimulated Thermal Scattering (ISTS) – was used that allows the generation and detection of narrow band surface acoustic waves (SAWs). The SAW velocity in a coated substrate is dispersive, i.e. the velocity depends on the wavelength (or frequency) of the SAW. The SAW penetration depth is of the same order as the wavelength. It is possible to measure this dispersion and, via fitting, to estimate the values of the elastic properties of the coating and/or the substrate. On a longer timescale the thermal expansion is washed out due to thermal diffusion. The photoacoustical and photothermal parts of the detected signal were analyzed and the elastic constants of martensite and austenite and thermal diffusivity were determined.