Achieving Giant Magnetically Induced Reorientation of Martensitic Variants in Magnetic Shape‐Memory Ni–Mn–Ga Films by Microstructure Engineering

Ranzieri, Paolo; Campanini, Marco; Fabbrici, S.; Nasi, L.; Casoli, F.; Cabassi, R.; Buffagni, E.; Grillo, Vincenzo; Magén, Cesar; Celegato, Federica; Barrera, Gabriele; Tiberto, P.; Albertini, F.

doi:10.1002/adma.201502072

Cited by 36 publications

(36 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The magnetic shape memory effect (MSE) is based on the magnetic field induced reorganization of martensitic variants in ferromagnetic shape memory alloys since this detwinning process results in large macroscopic deformations [1][2][3][4][5][6][7][8]. This fast and large superplastic deformation can be used in different applications such as in shape morphing or actuators [1,3,4].…”

Section: Introductionmentioning

confidence: 99%

Magnetic field induced random pulse trains of magnetic and acoustic noises in martensitic single-crystal Ni2MnGa

et al. 2017

View full text Add to dashboard Cite

Jerky magnetic and acoustic noises were evoked in a single variant martensitic Ni 2 MnGa single crystal (produced by uniaxial compression) by application of an external magnetic field along the hard magnetization direction. It is shown that after reaching the detwinning threshold, spontaneous reorientation of martensite variants (twins) leads not only to acoustic emission but magnetic two-directional noises as well. At small magnetic fields, below the above threshold, unidirectional magnetic emission is also observed and attributed to a Barkhausen-type noise due to magnetic domain wall motions during magnetization along the hard direction. After the above first run, in cycles of decreasing and increasing magnetic field, at low-field values, weak, unidirectional Barkhausen noise is detected and attributed to the discontinuous motion of domain walls during magnetization along the easy magnetization direction. The magnetic noise is also measured by constraining the sample in the same initial variant state along the hard direction and, after the unidirectional noise (as obtained also in the first run), a two-directional noise package is developed and it is attributed to domain rotations. From the statistical analysis of the above noises, the critical exponents, characterizing the power-law behavior, are calculated and compared with each other and with the literature data. Time correlations within the magnetic as well as acoustic signals lead to a common scaled power function (with β = −1.25 exponent) for both types of signals.

show abstract

Section: Introductionmentioning

confidence: 99%

Magnetic field induced random pulse trains of magnetic and acoustic noises in martensitic single-crystal Ni2MnGa

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The magnetization follows the easy axis in each martensitic variant and the overall pattern resembles the magnetic staircase pattern. We would like to emphasize that this domain pattern type exactly reproduces the magnetic structure, which has previously been observed both experimentally 13,17,23 at zero field in Ni-Mn-Ga films with similar martensitic structure and by comparable micromagnetic simulations. 23 The second step at H C is related to a magnetization configuration change solely in twin domain Y2 (states (c) and (d)).…”

mentioning

confidence: 74%

“…[10][11][12][13] It is remarkable that the reported values of the switching field are similar despite different growth techniques, sample orientations, and used substrates. In the following, we will show that this behavior can be explained on the basis of the model, which assumes the martensitic twin variant structure as fixed and only considers the magnetostatic interactions and the evolution of magnetic domains.…”

mentioning

confidence: 76%

“…[10][11][12][13] In analogy to bulk materials, this effect has also been identified as MIR of twin variants. However, a conclusive MIR model for thin films on a rigid substrate is still missing, owing to the fact that the substrate inhibits any macroscopic length change and thus hampers the magnetically induced change in the martensitic microstructure of an MSM film.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

Laptev

Lebecki

Welker

et al. 2016

Applied Physics Letters

View full text Add to dashboard Cite

We study the temperature dependent magnetization properties of (010)-oriented Ni-Mn-Ga epitaxial films on MgO(001) substrates. In the martensitic phase, we observe pronounced abrupt slope changes in the magnetization loops for all studied samples. Our experimental findings are discussed in conjunction with the micromagnetic simulations, revealing that the characteristic magnetization behavior is governed solely by the magnetization switching within the specific martensitic variant pattern, and no reorientation of twin variants is involved in the process. Our study emphasizes the important role of the magnetostatic interactions in the magnetization behavior of magnetic shape memory alloy thin films. Published by AIP Publishing.[http://dx.doi.org/10.1063/1.4963264] Magnetic shape memory (MSM) alloys exhibit a remarkable functional property to generate macroscopic strains upon exposure to a magnetic field of sufficient strength. 1,2 The strong coupling between the structural and magnetic degrees of freedom gives rise to the magnetically induced reorientation (MIR) of the twinned martensitic microstructure, resulting in a magnetic field-induced strain (MFIS). Strain values of up to 12% were reported for single crystals, 3-5 boosting the research interest especially in MSM thin films, which have a strong application potential in sensing and actuation systems. [6][7][8] In particular, the investigation of twin variant reorientation in epitaxial films has been the subject of several studies. However, the direct identification of the change of microstructure or the shape upon the application of external magnetic fields in thin films is a challenging task. Therefore, in analogy to bulk material studies, 9 magnetization measurements have been utilized in order to identify the MIR of twin variants. The reorientation of martensitic variants is linked to the reorientation of the easy magnetization axis, resulting in a strong change of the measured magnetization of the sample.A step-like increase in the magnetization has indeed been observed in constrained epitaxial thin films grown on different substrates. [10][11][12][13] In analogy to bulk materials, this effect has also been identified as MIR of twin variants. However, a conclusive MIR model for thin films on a rigid substrate is still missing, owing to the fact that the substrate inhibits any macroscopic length change and thus hampers the magnetically induced change in the martensitic microstructure of an MSM film.In this paper, we address the origin of steps in the magnetization loops of constrained epitaxial MSM films. We study the role of the martensitic microstructure and the magnetostatic interactions on the magnetization process of epitaxial Ni-Mn-Ga films on a rigid substrate. We employ temperature-dependent magnetization measurements and micromagnetic simulations to develop a model, which consistently explains the peculiar magnetization behavior.For this study, we use three epitaxial Ni-Mn-Ga film samples with different thicknesses (see Table I), prepared by DC m...

show abstract

“…The twin boundary traces at the film surface are oriented along ⟨100⟩ directions and hence along the diagonals of the SEM images. The second type of microstructure, "type Y" 36,38 or "low contrast zone," 39 has the b-axis of all martensitic variants out of plane. The twin boundaries are also c-a-twin boundaries that coincide with (110) or (110) planes which are perpendicular to the film plane.…”

mentioning

confidence: 99%

Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

et al. 2016

View full text Add to dashboard Cite

Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

show abstract

Achieving Giant Magnetically Induced Reorientation of Martensitic Variants in Magnetic Shape‐Memory Ni–Mn–Ga Films by Microstructure Engineering

Cited by 36 publications

References 26 publications

Magnetic field induced random pulse trains of magnetic and acoustic noises in martensitic single-crystal Ni2MnGa

Magnetic field induced random pulse trains of magnetic and acoustic noises in martensitic single-crystal Ni2MnGa

Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

Contact Info

Product

Resources

About