Effects of demagnetization on Magnetic-Field-Induced Strain and microstructural evolution in Ni-Mn-Ga Ferromagnetic Shape Memory Alloy by phase-field simulations

Qi, Peng; Huang, Junjie; Chen, Mingxiang

doi:10.1016/j.matdes.2016.06.050

Cited by 14 publications

(7 citation statements)

References 37 publications

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“…The internal field resulted in varying magnetization across the sample, which gave rise to inhomogeneous Maxwell stress. Peng showed a similar effect with phase-field simulations [97]. As the width of a specimen decreased by two orders of magnitude the critical field increased by a factor of two and the field required to saturate the material increased by a factor of four [98].…”

Section: Transmission Electron Microscopysupporting

confidence: 59%

Effects of the Internal Magnetic Field on the Magneto-Mechanical Properties of Magnetic Shape Memory Alloys

Hobza¹

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Shape memory alloys are a class of functional material which recover from large strains without permanent deformation. The strain is accommodated by the displacement of twin boundaries in the martensite phase. The shape memory alloy Ni-Mn-Ga is also ferromagnetic. Ni-Mn-Ga preferentially magnetizes along a certain crystallographic axis. This direction of easy magnetization changes across twin boundaries, such that the directions in neighboring twin domains are nearly perpendicular. The interaction of magnetic moments and interfaces including the crystal surface and twin boundary interfaces has a large role in the magnetization process of the material. The goal of this study is to characterize the relative influence of twin boundaries on the magnetization of the material, and the dependence of the magnetization on the twin domain microstructure. The torque on a single crystal specimen in a homogeneous external magnetic field was characterized with experimental methods. The torque is the negative first derivative of the magnetic energy as a function of angle between the specimen and magnetic field. The torque and magnetic energy strongly depends on the twin domain microstructure. For specimen with two twin boundaries at 3% strain in an external magnetic field of 50 mT, one twin microstructure required 1.7 times more torque to rotate than another twin microstructure. At fields above 100 mT, the torque was asymmetric depending on the direction the direction the sample was rotated. vii Numerical micromagnetic simulations were performed to gain a qualitative understanding of the difference in magnetization and magnetic energy in different twin microstructures. At low fields, the continuity of magnetization across the twin boundary results in one twin microstructure having completely saturated twin domains, while the other microstructures contained 180° magnetic domains. At larger fields, the asymmetry in torque was due to the angle of the twin boundary with the crystal surface. Both the dependence on magnetization and torque asymmetry are due to the internal magnetic field at the twin boundary. The interaction of magnetic moments across the twin boundary drives the internal magnetic field and magnetization. The twin domain microstructure can be manipulated to drive the magnetization process in order to optimize the performance of the material in a device. The role of the internal magnetic field and specimen magnetization is discussed regarding a low power strain sensing measurement technique. viii TABLE OF CONTENTS

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Section: Transmission Electron Microscopysupporting

confidence: 59%

Effects of the Internal Magnetic Field on the Magneto-Mechanical Properties of Magnetic Shape Memory Alloys

Hobza¹

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“…The field of micromagnetics was pioneered by Brown [20] and a comprehensive review was presented by Chantrell et al [21]. Many research groups have used micromagnetics to characterize mesoscale magnetic properties of Ni-Mn-Ga alloys [22][23][24][25][26][27][28][29]. The theory of solving the Landau-Lifshitz dynamic equation was applied with various methods such as phase field modeling [23][24][25][28][29][30].…”

Section: Micromagneticsmentioning

confidence: 99%

“…Many research groups have used micromagnetics to characterize mesoscale magnetic properties of Ni-Mn-Ga alloys [22][23][24][25][26][27][28][29]. The theory of solving the Landau-Lifshitz dynamic equation was applied with various methods such as phase field modeling [23][24][25][28][29][30]. This method has been used to study the twin boundary mobility [23], magnetic domain evolutions [30], demagnetization effects [29], and magneto-mechanical properties [24,25] of Ni-Mn-Ga.…”

Section: Micromagneticsmentioning

confidence: 99%

Sensitivity of twin boundary movement to sample orientation and magnetic field direction in Ni-Mn-Ga

et al. 2020

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When applying a magnetic field parallel or perpendicular to the long edge of a parallelepiped Ni-Mn-Ga stick, twin boundaries move instantaneously or gradullay through the sample. We evaluate the sample shape dependence on twin boundary motion with a micromagnetics computational study of magnetic domain structures and their energies. Due to the sample shape, the demagnetization factor varies with the direction of external magnetic field. When the external magnetic field is applied perpendicular to the long edge of the sample, i.e. in the direction in which the demagnetizing field is highest, the magnetic energy intermittently increases when the strength 2 of the applied magnetic field is low. This energy gain hinders the twin boundary motion and results in a gradual switching, i.e. a gradual magnetization reversal as the applied magnetic field is increased. The formation of 180⁰ magnetic domains offsets this effect partially. In contrast, when the applied magnetic field is parallel to the long edge of the sample, i.e. in the direction in which the demagnetizing field is lowest, the energy decreases with each subsequent magnetization domain reversal and the twin boundary moves instantaneously with ongoing switching. The actuation mode with the field parallel to the long sample edge lends itself for on-off actuators whereas the actuation mode with the field perpendicular to the long sample edge lends itself to gradual positioning devices.

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“…Many research groups have characterized the mechanical properties of these MSM alloys with and without a magnetic field [5][6][7][8]. Other research groups have studied the magnetic domains [9][10][11][12][13][14][15] and twin boundary structure, type, and mobility [15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Magnetic domain-twin boundary interactions in Ni–Mn–Ga

2020

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The stress required for the propagation of twin boundaries in a sample with fine twins increases monotonically with ongoing deformation. In contrast, for samples with a single twin boundary, the stress exhibits a plateau over the entire twinning deformation range. We evaluate the twin boundary and magnetic domain boundary interactions for increasing twin densities. As the twinned regions get finer, these interaction regions result in additional magnetic domains that form magnetoelastic defects with high magnetostress concentrations. These magnetoelastic defects act as obstacles for twinning disconnections and, thus, harden the material. Whereas in a low twin density microstructure, these high-energy concentrations are absent or dilute and their effectiveness is reduced by the synergistic action of many twinning disconnections. Therefore, with increasing twin density, the interaction of twin boundary and magnetic domain boundaries reduces the twin boundary mobility. The defect strength has a distribution such that twinning 2 disconnections overcome soft obstacles first and harder obstacles with ongoing deformation. The width of the distribution of obstacle strength and the density of obstacles increase with increasing twin density and, thus, the hardening coefficient increases with increasing twin density.

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Effects of demagnetization on Magnetic-Field-Induced Strain and microstructural evolution in Ni-Mn-Ga Ferromagnetic Shape Memory Alloy by phase-field simulations

Cited by 14 publications

References 37 publications

Effects of the Internal Magnetic Field on the Magneto-Mechanical Properties of Magnetic Shape Memory Alloys

Effects of the Internal Magnetic Field on the Magneto-Mechanical Properties of Magnetic Shape Memory Alloys

Sensitivity of twin boundary movement to sample orientation and magnetic field direction in Ni-Mn-Ga

Magnetic domain-twin boundary interactions in Ni–Mn–Ga

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