Magnetomechanical Four‐State Memory

Watson, Chad S.; Hollar, Courtney; Anderson, Kimball; Knowlton, William B.; Müllner, Peter

doi:10.1002/adfm.201203015

Cited by 27 publications

(11 citation statements)

References 39 publications

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“…[10][11][12] While reducing the sample size increases blocking stress up to 10 MPa, 13 fewer twinning dislocations-which are the vehicles that transport preferentially aligned martensite variants-are present at small length scales. As a result, higher stresses may be required to initiate twin boundary movement in smaller samples, competing with the fundamental actuating functionality of Ni-Mn-Ga. 14 Nanoindentation, either alone or in combination with scanning probe microscopy techniques such as atomic force microscopy (AFM) or magnetic force microscopy (MFM), has previously been applied to Ni-Mn-Ga to (i) evaluate the role of twinning during nanoscale deformations, 15,16 (ii) probe the local elastic properties of twin boundaries, 17 (iii) manipulate the local stray magnetic field for memory applications, 18 (iv) facilitate martensitic transformation for magnetocaloric applications, 19 and (v) demonstrate lattice softening in pre-martensitic Ni-Mn-Ga. 20 Of particular relevance to the current work, Ganor and Shilo showed that nanoindentation techniques can be used to resolve differences in reduced elastic modulus of martensitic Ni-Mn-Ga across 90 twin boundaries. 21 In that work, the authors identified anisotropy in the reduced elastic modulus of Ni-Mn-Ga, where the modulus measured perpendicular to the c-axis (i.e., for martensite variants exhibiting an in-plane c-axis orientation) was significantly less than that measured parallel to a)…”

Section: Introductionmentioning

confidence: 99%

“…AFM and MFM are a powerful combination, as together they can reveal changes in the twin structure and magnetic axis orientation at the nanoscale in response to applied thermomechanical stresses. 15,16,18,23 MFM is particularly useful and instructive in the case of FSMAs such as Ni-Mn-Ga, as it provides the ability to readily identify twins and the orientation of the easy magnetization axis (c-axis) at the nanoscale, which is not possible in the case of non-ferromagnetic shape memory alloys such as NiTi (nitinol).…”

Section: Introductionmentioning

confidence: 99%

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Localized deformation in Ni-Mn-Ga single crystals

Davis

Efaw

Patten

et al. 2018

Journal of Applied Physics

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The magnetomechanical behavior of ferromagnetic shape memory alloys such as Ni-Mn-Ga, and hence the relationship between structure and nanoscale magnetomechanical properties, is of interest for their potential applications in actuators. Furthermore, due to its crystal structure, the behavior of Ni-Mn-Ga is anisotropic. Accordingly, nanoindentation and magnetic force microscopy were used to probe the nanoscale mechanical and magnetic properties of electropolished single crystalline 10M martensitic Ni-Mn-Ga as a function of the crystallographic c-axis (easy magnetization) direction relative to the indentation surface (i.e., c-axis in-plane versus out-of-plane). Load-displacement curves from 5-10 mN indentations on in-plane regions exhibited pop-in during loading, whereas this phenomenon was absent in out-of-plane regions. Additionally, the reduced elastic modulus measured for the c-axis out-of-plane orientation was $50% greater than for in-plane. Although heating above the transition temperature to the austenitic phase followed by cooling to the room temperature martensitic phase led to partial recovery of the indentation deformation, the magnitude and direction of recovery depended on the original relative orientation of the crystallographic c-axis: positive recovery for the in-plane orientation versus negative recovery (i.e., increased indent depth) for out-of-plane. Moreover, the c-axis orientation for out-of-plane regions switched to in-plane upon thermal cycling, whereas the number of twins in the in-plane regions increased. We hypothesize that dislocation plasticity contributes to the permanent deformation, while pseudoelastic twinning causes pop-in during loading and large recovery during unloading in the c-axis in-plane case. Minimization of indent strain energy accounts for the observed changes in twin orientation and number following thermal cycling.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Localized deformation in Ni-Mn-Ga single crystals

Davis

Efaw

Patten

et al. 2018

Journal of Applied Physics

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“…The shape memory properties of Ni-Mn-Ga make it an ideal candidate for applications including micro-fluid pumps, energy harvesting, and memory devices [7][8][9][10][11]. For these uses, long fatigue life and fracture resistance are required when FSMAs are actuated thousands or even millions of times and failure caused by nucleation and propagation of cracks must be prevented.…”

Section: Introductionmentioning

confidence: 99%

Fatigue life and fracture mechanics of unconstrained Ni–Mn–Ga single crystals in a rotating magnetic field

Lawrence

Lindquist

Ullakko

et al. 2016

Materials Science and Engineering: A

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a b s t r a c tFracture resistance and long fatigue life are required to commercialize Ni-Mn-Ga ferromagnetic shape memory alloys. While Ni-Mn-Ga achieves high fatigue life at low strains, there is little data on the fatigue life of samples that are actuated near the theoretical strain limit. Furthermore, constraints imposed by clamping samples impact their magneto-mechanical and fatigue properties. Here, 10 M Ni-MnGa single crystals were exposed to a rotating magnetic field while holding them with rubber O-rings so they were minimally constrained. Prior to testing, sample surfaces were prepared to various levels of finish. Fatigue life varied with some samples reaching more than 800,000 cyclic loads before fracturing and some samples failing after only 4000 cyclic loads. Long fatigue life and fracture resistance are achieved when avoiding crystal defects and surface imperfections. Short fatigue life was caused by high surface roughness and stress concentration at defects and notches.

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“…In these materials, the magnetic moment is strongly coupled to the crystal lattice, and therefore the rotation of the magnetic moments by an external driving force can lead to a consequent rearrangement of crystal lattice in the form of twin reorientation. As a result, strong coupling between magnetic moments and crystallographic twin orientations can give rise to many interesting effects such as large magnetic-field-induced strains and memory effects in resistivity and magnetization, with potential applications in smart actuators and information storage [4][5][6][7]. Therefore, from both fundamental and technological viewpoints, it is of utmost importance to be able to quantitatively determine and model both magnetic moment rotation and twin reorientation, which can occur simultaneously under the application of magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Directin situmeasurement of coupled magnetostructural evolution in a ferromagnetic shape memory alloy and its theoretical modeling

et al. 2015

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Ferromagnetic shape memory alloys (FSMA) have shown great potential as active components in next generation smart devices due to their exceptionally large magnetic-fieldinduced strains and fast response times. During application of magnetic fields in FSMAs, as is common in several magnetoelastic smart materials, there occurs simultaneous rotation of magnetic moments and reorientation of twin variants, resolving which although critical for design of new materials and devices, has been difficult to achieve quantitatively with current characterization methods. At the same time, theoretical modeling of these phenomena also faced limitations due to uncertainties in values of physical properties such as magnetocrystalline anisotropy energy (MCA), especially for off-stoichiometric FSMA compositions. Here, in situ polarized neutron diffraction is used to measure directly the extents of both magnetic moments rotation and crystallographic twin-reorientation in an FSMA single-crystal during the application of magnetic fields. In addition, high-resolution neutron scattering measurements and first-principles calculations based on fully relativistic density functional theory are used to determine accurately the MCA for the compositionally disordered alloy of Ni 2 Mn 1.14 Ga 0.86 . The results from these state-of-the-art experiments and calculations are self-consistently described within a phenomenological framework, which provided quantitative insights into the energetics of magnetostructural coupling in FSMAs.Based on the current model, the energy for magnetoelastic twin boundaries propagation for the studied alloy is furthermore estimated to be ~150 kJ/m 3 .

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Magnetomechanical Four‐State Memory

Cited by 27 publications

References 39 publications

Localized deformation in Ni-Mn-Ga single crystals

Localized deformation in Ni-Mn-Ga single crystals

Fatigue life and fracture mechanics of unconstrained Ni–Mn–Ga single crystals in a rotating magnetic field

Directin situmeasurement of coupled magnetostructural evolution in a ferromagnetic shape memory alloy and its theoretical modeling

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