Magnetic Field-induced Strain Research Articles

Enhancement of microstructure-based magnetic, electronic, and lattice contribution in a CoNiAl ferromagnetic shape memory alloy

In this study, a Co-Ni-Al system with nominal compositions Co42​Ni31Al27​ and Co41Ni32Al27​ was synthesized. The structural and microstructure of these confirm the presence of a non-ferromagnetic face-centered cubic (γ) phase interspersed between the grains of a ferromagnetic body-centered cubic (β) phase. Notably, γ phase is increased by 1.5 times in the Co41Ni32Al27 sample due to the 1% substitution of Co by Ni. The microstructural tuning induced a higher thermal hysteresis in the shape memory effect of Co41​Ni32Al27 with an increase in enthalpy during the phase transition (Austenitic↔Martensitic). In addition, the temperature-dependent resistivity, ρ(T) was measured to study the electron-phonon and electron-magnon scattering around the phase transition of the studied samples. The dynamic elastic properties of the studied samples were tracked by the relative change in sound velocity (δv/v) with temperature and elastic recovery was confirmed in both alloys across the 120 K to 300 K range. However, the Co41​Ni32Al27​ exhibits a high amount of lattice contribution to the shape recovery compared to the Co42​Ni31Al27​. Moreover, a larger variation in relative resistivity (Δρ/ρ) for Co41Ni32Al27 compared to Co42​Ni31Al27 during the phase transition indicates a larger shape change due to decreased Co content. Furthermore, the Co41Ni32Al27 sample shows higher temperatures of martensitic start (TMs ≈ 260K) and Austenitic finish (TAf ≈ 290K) along with high Curie temperature (Tc = 330K). Consequently, the temperature-dependent susceptibility (χ′) confirms the higher magnetoelastic recovery in the Co41Ni32Al27 sample, indicating an enhancement of magnetic field-induced strain (MFIS). Stress-induced Q−1 is lower for Co41Ni32Al27 (∼2.9×10−3) compared to Co42Ni31Al27 sample (∼5.0×10−3) signifying the enhanced mechanical strength.

Coupled magneto-mechanical response of laminate composites comprising a layer of Ni-Mn-Ga microparticles

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs), exhibiting a giant magnetic field induced strain (MFIS), high work output and fast response, are highly promising materials for emerging technologies to be used in automotive, aerospace, and robotics industries, among others. Their magnetic-to-mechanical energy conversion ability is characterized by the coupled magneto-mechanical response they show when magnetic field and mechanical stress are simultaneously applied. In the present work we elaborated a series of laminated composites comprising a layered ensemble of single crystalline Ni-Mn-Ga microparticles built-in between Cu foils via small layers of silicone rubber. Such a simple and robust design enabled an in-depth study of the simultaneous influence of the magnetic field and compressive opposing stress on MFIS and the generated force of the particle layer driving out-of-plane magnetomechanical response of the laminate. Self-consistent parameters characterizing a magnetic field- and stress-induced martensitic variant reorientation in the particles were disclosed by the measurements and comprehensive analysis of both the magnetization curves under opposing constant stresses (complemented by tracking residual strains with X-ray µ-CT imaging) and compressive stress-strain dependences under transversal magnetic field. In particular, an accurate value of the magnetic-to-mechanical energy conversion coefficient, equal to Cme = (2.3 ± 0.13) MPa/T2, and the value of maximum magnetostress of about 2.3 MPa generated by microparticles were determined, in a good agreement with bulk Ni-Mn-Ga single crystals (SC). In contrast to bulk SC, particles are technologically and costly more efficient. They have much higher degree of freedom in terms of composites design allowing the development of advanced miniature actuators and sensors.

Characterization of hydrophobic metasurfaces fabricated on Ni-Mn-Ga-based alloys using femtosecond pulsed laser ablation

The generation of hydrophobic surfaces through laser ablation has garnered considerable attention, particularly for its prospective diverse applications across various industries. This study explores the possibility of generating controllable hydrophobic metasurfaces on Ni-Mn-Ga-based magnetic shape memory (MSM) alloys using femtosecond pulse width laser (FPWL). While hydrophobic surfaces have been achieved on different materials through a variety of different techniques, the research marks the first systematic attempt to tailor hydrophobicity on the surface of Ni-Mn-Ga-based alloys. By characterizing surfaces treated with different laser parameters, the distinct morphologies and hydrophobic properties corresponding to each surface were identified. This newfound control over surface properties with specific machining parameters opens possibilities for applications in microfluidic devices. Additionally, the potential of utilizing the magnetic-field-induced strain (MFIS) exhibited by Ni-Mn-Ga single crystals to alter surface hydrophobicity was explored. Metasurfaces mimicking the dimensional changes in elongation induced by MFIS demonstrated higher static contact angles (SCAs) for water droplets compared to the original surfaces. This approach presents a promising avenue for creating multifunctional microdevices with controllable hydrophobicity using Ni-Mn-Ga-based alloys. Our findings not only offer insights into tailoring of hydrophobic/hydrophilic properties on Ni-Mn-Ga-based MSM alloys but also provide a novel methodology for fabricating functional metasurfaces on other metals.

Enhanced metamagnetic shape memory effect in Heusler-type Ni37Co11Mn43Sn9 polycrystalline ferromagnetic shape memory alloy

Polycrystalline Ni-Co-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) show promise as actuator materials, but their practical application involving magnetic field induced strain (MFIS) is often limited by three factors: the requirement for high magnetic fields (> 5 T), martensitic transition temperature away from room temperature, and limited recovery of pre-strain applied to the martensite phase. Current work investigates the martensitic transition and shape memory effect under the application of magnetic field for bulk polycrystalline Ni37Co11Mn43Sn9 alloy. The outcome of the study reveals a metamagnetic transition from the martensitic phase to the austenitic phase at a low field of 2.8 T at 300 K which results 0.25 % spontaneous MFIS. Interestingly, 1.3 % pre-strained specimen registers a 100 % recovery with the application of magnetic field of 4.5 T. Furthermore, the pre-strained specimen exhibited a two-way shape memory effect between a strain value of 1.0 % to 1.55 % during the field loading and unloading sequences. Notably, this study demonstrates, for the first time to the best of our knowledge that the spontaneous MFIS and pre-strain add together. This finding paves the way for achieving a giant MFIS by pre-straining a Ni-Mn-Sn/In class of FSMAs which shows large spontaneous MFIS.

In-situ alloying laser powder bed fusion of Ni-Mn-Ga magnetic shape memory alloy using liquid Ga

Ni-Mn-Ga-based magnetic shape memory alloys can exhibit large magnetic field induced strains (MFIS). Recently, additive manufacturing techniques, especially laser powder bed fusion (L-PBF), have been successfully used to manufacture functional polycrystalline Ni-Mn-Ga with complex geometries, such as ‘bamboo-grained’ lattice structures. However, previous approaches of L-PBF of Ni-Mn-Ga have used pre-alloyed powders, which can limit the compositional freedom of the manufactured devices. This study explores, for the first time, the feasibility of an in-situ L-PBF alloying approach using a powder blend of elemental Ni, Mn, and Ga. Promising results were obtained despite the significant differences between the elemental Ni and Mn powders and the liquid Ga. The microstructure of the as-built sample showed distinct stripe patterns from the 14 M structure confirmed by XRD analysis. Heat-treatment significantly improved chemical homogeneity, dissolved the Ni-rich phase but couldn’t dissolve MnO hindering the shape memory effect.

Analytical 3D model for coupled magneto-mechanical behaviors of ferromagnetic shape memory alloy

Ferromagnetic shape memory alloys (FSMA), a type of smart material, are promising for engineering applications due to their large, high-frequency, and reversible magnetic-field-induced-strain (MFIS). However, the magneto-mechanical behaviors of FSMA are still not well understood due to the intrinsically coupled and cross-scale magneto-mechanical responses, limiting the design and optimization of FSMA-based devices such as sensors and actuators. In this work, a fully-analytical 3D model containing only basic material parameters and incorporating all key mechanisms for the magneto-mechanical performances of FSMA is developed based on a new magneto-mechano-decoupled energy minimization approach. It is shown that the coupled magneto-mechanical responses of FSMA-based sensors (cyclic stress with constant magnetic field) and actuators (cyclic magnetic field with constant stress) predicted by the model are in excellent agreement with existing experimental measurements. Based on these analytical predictions, the optimal ranges for the constant field and demagnetization factor are determined to achieve simultaneous complete strain recovery and considerable magnetization change as required by the FSMA-based sensors. In addition, the dependences of switching and saturating fields of MFIS on the constant stress and demagnetization factor are quantified for the FSMA-based actuators. Finally, a phase diagram is constructed to quantitatively determine the critical magnetic fields and stresses for predicting the strain induction and recovery under various loading conditions. The analytical model provides a simple, reliable, and versatile tool to reveal the comprehensive mechanisms for the coupled magneto-mechanical behaviors of FSMA and to guide the design of FSMA-based sensors and actuators with customized and on-demand performances.

Unexpected modulation revealed by electron diffraction in Ni-Mn-Ga-Co-Cu tetragonal martensite exhibiting giant magnetic field-induced strain

Although the modulation of martensite structure has been considered as a precondition for highly mobile twin boundary and thus a giant magnetic field induced strain, the largest strain to date has been reported in non-modulated tetragonal martensite of Ni-Mn-Ga-Co-Cu. Using high-resolution transmission electron microscopy (HRTEM), we found that nominally non-modulated tetragonal Ni46Mn24Ga22Co4Cu4 single crystal possesses a modulation. The modulation was observed in thin lamellae containing b/c twins prepared by a focused Ga-ion beam and on a sample prepared by a conventional wedge thinning method. The modulation vector q* = (0, 0.2554, 0.4642), was determined by 3D electron diffraction. The simulated HRTEM image of such a structure agrees with the HRTEM micrograph. The presence of modulation in the thin lamellae and not in bulk suggests that Ni-Mn-Ga-Co-Cu martensite is on the edge of the shear instability enabling the high mobility of twin boundaries.

Effects of machining parameters on Ni-Mn-Ga-based alloys for fabrication of multifunctional micro devices using femtosecond pulse width laser

Ni-Mn-Ga-based magnetic shape memory (MSM) alloy single crystals are known for their large magnetic-field-induced strain (MFIS). This quality makes them a promising material for use in micro actuators and devices. However, the manufacturing of single-crystal-based Ni-Mn-Ga micro actuators is challenging due to their high brittleness and other material properties – numerous machining techniques that are successfully used for the deep engraving of conventional engineering materials cannot be directly applied to Ni-Mn-Ga-based alloys. Nevertheless, previous studies have shown that a femtosecond pulse width laser (FPWL) can be successfully utilized for the defect-free micromachining various materials. This work studies the effects of different engraving parameters and introduces a novel scanning-based method for the deep micromachining of Ni-Mn-Ga-based MSM alloys with maximum surface quality. Results show that a 4-layer strategy with a 0.01 mm hatch distance provides excellent machining in terms of surface quality and dimensional accuracy. This study can be utilized within design stages to estimate minimum margin based on required machined depth and avoid defects that occur in the sample preparation stage. Additionally, evolution of structures generated by FPWL machining are characterized. The results highlight how FPWL can be considered a highly capable process for the micromachining and surface structuring of Ni-Mn-Ga-based single crystals for manufacturing multifunctional MSM microdevices.

Magnetostriction and volume magnetostriction of sputtered Tb20Fe24Co56 film

The magnetostriction and volume magnetostriction of sputtered amorphous Tb20Fe24Co56 (TFC) films are investigated. In recent years, knowledge of volume magnetostriction is needed in terms of actuator applications utilizing the volume magnetostriction effect. This TFC film with the composition selected in this study is known to exhibit small Joule magnetostriction in Tb-Fe-Co system, and the volume magnetostriction of Tb-Fe-Co thin film systems may be observed more significantly. A bilayer cantilever structure is used to evaluate the magnetostriction performance, which indicates that the largest magnetostriction coefficient and volume magnetostriction of the TFC films are 54 and 48 ppm at an external magnetic field of 7490 Oe, respectively. The Ar gas pressure during sputter deposition is selected to be in the range of 0.7 to 8 Pa in consideration of the deposition quality of the TFC film. The residual stress shifts to the tensile side as the Ar gas pressure increases while the stress field affects the magnetostriction performance. The value of the Joule magnetostriction of the TFC film is almost as same as the volume magnetostriction, which shows that the volume magnetostriction is the dominant mechanism of the magnetic field-induced strain. The homogeneous distribution of elements in the amorphous TFC films possibly makes the Joule magnetostriction small. Since the magnetization of the TFC film is sensitive to strain, the stress field in the in-plane direction strongly constrains the magnetic moment in the out-of-plane direction, and this constraint affects the magnetostriction and magnetization properties. This strain-sensitive magnetic film opens up new possibilities for microdevices using magnetostrictive TFC films via volume magnetostriction.

Phase Field Simulations of Microstructures in Porous Ferromagnetic Shape Memory Alloy Ni2MnGa

The magnetic domain structures and martensite microstructures of porous Ni2MnGa Heusler alloys with various circle-shaped and ellipse-shaped pores were systematically studied by the phase field method. The magnetization curves and magnetic field-induced strains (MFIS) at the external field were determined. A mesoscopic mechanism was proposed for simulation to reveal the influence of the pores on the microstructures and the MFIS of porous magnetic shape memory alloy. The stress concentration effect and the recovery strain of the porous alloy are studied. The results indicate the MFIS value increases when ellipse-shaped pores elongate along the twin boundary. The effects of porosity and pore size on MFIS for porous Ni-Mn-Ga alloys with randomly distributed pores were also explored. The present study is of guiding significance for understanding the role played by pores on the MFIS and may provide a possible way to adjust the functional properties of ferromagnetic shape memory alloys.

Toughening of Ni-Mn-Based Polycrystalline Ferromagnetic Shape Memory Alloys.

Solid-state refrigeration technology is expected to replace conventional gas compression refrigeration technology because it is environmentally friendly and highly efficient. Among various solid-state magnetocaloric materials, Ni-Mn-based ferromagnetic shape memory alloys (SMAs) have attracted widespread attention due to their multifunctional properties, such as their magnetocaloric effect, elastocaloric effect, barocaloric effect, magnetoresistance, magnetic field-induced strain, etc. Recently, a series of in-depth studies on the thermal effects of Ni-Mn-based magnetic SMAs have been carried out, and numerous research results have been obtained. It has been found that poor toughness and cyclic stability greatly limit the practical application of magnetic SMAs in solid-state refrigeration. In this review, the influences of element doping, microstructure design, and the size effect on the strength and toughness of Ni-Mn-based ferromagnetic SMAs and their underlying mechanisms are systematically summarized. The pros and cons of different methods in enhancing the toughness of Ni-Mn-based SMAs are compared, and the unresolved issues are analyzed. The main research directions of Ni-Mn-based ferromagnetic SMAs are proposed and discussed, which are of scientific and technological significance and could promote the application of Ni-Mn-based ferromagnetic SMAs in various fields.

Phase stability and physical property for off-stoichiometric Ni-Mn-Sb alloys including 4O phase

Large magnetic field-induced strains can only be found in modulated martensite for Ni-Mn-Sb alloys, but the theoretical research on this alloy which is generally concentrated in the austenite and non-modulated martensite (NM) ignores the modulated martensite. Therefore, in this paper, we systematically study the relationship between phase stability, physical property and composition in the full series Ni-Mn-Sb Heusler alloys (Ni24+xMn12-xSb12, Ni24+xMn12Sb12-x, Ni24-xMn12+xSb12, Ni24Mn12+xSb12-x) including four-layered orthorhombic modulated martensite (4O) by the first principles calculations. For phase stability, we determined that the critical components of 4O for Ni24+xMn12-xSb12, Ni24+xMn12Sb12-x and Ni24Mn12+xSb12-x is × = 6, x = 6 and × = 4, respectively. There is no 4O phase within the concentration range considered for Ni24-xMn12+xSb12. Moreover, the martensitic transformation sequences are also determined. As for physical properties, the transformation temperatures from austenite to 4O and NM phases are predicted respectively. Meanwhile, the ternary magnetic moment diagram of austenite, 4O and NM phases is constructed. The maximum value of total magnetic moment is distributed in the Ni-excess Sb-deficient system, while the minimum value of that is distributed in the Mn-excess Sb-deficient system. The origin of the above observations is explained by the competition between the Jahn-Teller effect in the electronic structure and the strength of the covalent bond. The results in this paper are expected to provide information for the composition design and performance optimization of Ni-Mn-Sb alloy.

Enhanced magnetic-field-induced strain of Ni-Mn-In alloy by altering laser scanning strategy during laser powder bed fusion

Dense polycrystalline Ni-Mn-In alloy specimens were fabricated by utilizing two laser scanning strategies of laser powder bed fusion (L-PBF) technology for the first time. The effect of scanning strategies on the microstructure, crystals texture and magnetic-field-induced strain (MFIS) were investigated systematically. The results showed that the uniformly sized grains were formed in samples with unidirectional scanning strategy, while the bidirectional scanning strategy leads to a bimodal distribution of grains. The MFIS value in unidirectional strategy increased over twofold, rising from 403 ppm to 820 ppm. This work opens a new insight into regulating process parameters and customizing the microstructure and overall magnetic properties of Ni-Mn-In alloys in the additive manufacturing field.

Selective Etch for Micromachining Process in Manufacturing Hybrid Microdevices composed of Ni-Mn-Ga and Silicon Layers

The goal of this study is to make selective etch possible for the next generation of MEMS(microelectromechanical systems) devices that are composed Ni-Mn-Ga and silicon layers. Due tothe large magnetic-field-induced strains of Ni-Mn-Ga, sensing and actuating components can be fab-ricated in the Ni-Mn-Ga layers. Other functional components can be manufactured in the silicon layer.Single crystalline Ni-Mn-Ga alloys that are grown by using the Bridgman vertical growth techniquehave so far obtained the largest magnetic field-induced strain (MFIS), a magnetic shape memory(MSM) effect. Similar to silicon wafers, Ni-Mn-Ga wafers are also sliced from crystal-oriented singlecrystalline ingots. To fabricate hybrid MEMS devices such as micromanipulators and robots, lab-on-chip containing micropump manifolds and valves, or vibration energy harvesters, the fabricationprocesses used for MEMS devices will be also used to fabricate components in the Ni-Mn-Ga layer ofthe hybrid MEMS devices. One of the most important processes for MEMS fabrication is the structur-ing of materials by chemical etching. The main goal of this study is to obtain evidence that the etchantetches silicon but not Ni-Mn-Ga and to identify an etchant that etches Ni-Mn-Ga but not silicon. Thepresent paper reports on a novel experiment in dissolving Ni-Mn-Ga alloys. An etchant compositionof 69% HNO3, 98% H2SO4, and CuSO4•5H2O is proposed for dissolving Ni-Mn-Ga alloys and thevariation in the dissolution rate by adjusting the concentrations of HNO3 and ultrapure water (UPW)is demonstrated. This etchant was demonstrated to etch Ni-Mn-Ga but not silicon. The HF+HNO3acidic solution commonly used for etching silicon does not dissolve Ni-Mn-Ga alloys.

Framework of magnetostrain responsive Ni–Mn–Ga microparticles driving magnetic field induced out-of-plane actuation of laminate composite

Ni–Mn–Ga single crystals (SC) exhibiting a giant magnetic field induced strain (MFIS), resulting from twin boundaries rearrangements, are excellent materials for novel actuators although enhanced brittleness and high costs are remaining the issues for applications. In polycrystalline state Ni–Mn–Ga alloys show small MFIS due to grain boundary constraints. By simple size reduction of the mentioned materials it is hardly possible to create quasi-two-dimensional MFIS actuators on the microscale with a pertinent out-of-plane performance. In pursuit of the trend for next generation materials and functions by design, in the present work we have developed a laminate composite as a prototype of microactuator with the out-of-plane stroke being driven by a framework of magnetostrain responsive Ni–Mn–Ga microparticles. The laminate consisted of the layer of crystallographically oriented Ni–Mn–Ga semi-free SC microparticles sandwiched between bonding polymer and Cu foils. Such design provided a particles isolation with a minimum constraint condition from the polymer. MFIS of the individual particles and the whole laminate composite was investigated by X-ray micro-CT 3D imaging. Both particles and laminate exhibited the same recoverable out-of-plane stroke produced by the particles´ MFIS of around 3% under 0.9 T. The developed microactuator design is promising for applications in the areas of micro-robotics, optical image stabilization in cameras, pumps for microfluidics etc.

Transformation strain and volume effect associated with martensitic transformation in polycrystalline Ni49+x+yMn23-xGa28-y Heusler alloys

Combined thermal strain and magnetization measurements were performed in polycrystalline alloys Ni49.31Mn22.76Ga27.93(Ni49), Ni53.00Mn21.04Ga25.96(Ni53) and Ni55.62Mn17.52Ga26.86(Ni55.5) to understand the influence of magnetic field (B) on transformation strain (Δλ) and relative volume change (ω) at martensitic transformation (MT). It is found that during cooling and heating both Ni49 and Ni53 samples undergo a MT while the Ni55.5 sample experiences a coupled magnetostructural transformation (MST). Such a MST can enhance the Δλ and ω whereas thermal hysteresis weakens them, which results in a non-monotonic variation in Δλ: 0.211% (Ni49) → 0.166% (Ni53) → 0.185% (Ni55.5) under B = 0 T. Similar tendency was observed in ω. Besides, the values of Δλ and ω increase with increasing field, partially due to the contribution of magnetic field-induced strain. The maximum value ω = 0.674% was obtained in Ni49 sample under 3 T, indicating that an extra volume space of ∼1% should be needed to avoid the destruction of refrigeration chamber. These findings provide key information for future use of Ni–Mn-Ga alloys in refrigeration engineering field.

Aging behavior of Ni-Mn-Ga/silicone particulate composites exhibiting large recoverable magnetostrain

Single crystalline Ni-Mn-Ga particles/silicone composites are new ferromagnetic shape memory materials, exhibiting a large reversible magnetic field induced strain (MFIS), are greatly demanded for actuators and sensors toward future technologies. In the present work, we studied a long-term aging effect on the mechanical and recoverable MFIS properties of the Ni-Mn-Ga/silicone particulate composites containing different amounts of filler. It was shown that despite a strong decline of the effective stiffness of pure silicone during long aging, the stiffness reduction of composites was much less pronounced and barely affected the characteristics of the large recoverable MFIS.

Enhanced magnetic properties and magnetic field induced strain in polycrystalline NiMnGa alloy by electron irradiation

High saturation magnetization (Ms) and magnetocrystalline anisotropy constant (Ku) are essential to achieve high magnetic field induced strain (MFIS) in NiMnGa alloys. These magnetic properties are closely related to the local electronic structure and intrinsic magnetic moment. In the present study, point defects were induced by electron irradiation to modify lattice distortion leading to the variation of Mn-Mn atoms. The Ms and Ku were enhanced providing higher driving force for variant movement. Then the MFIS of polycrystalline NiMnGa alloys can be increased from 200 ppm to 700 ppm. This research provides a new idea to enhance magnetic properties and magnetic field induced strain.

Multifunctionality in ferromagnetic shape memory alloy-based resistive switching memory for flexible ReRAM application

Multifunctional flexible electronics is the ongoing demand for fabricating wearable data storage and communication devices. The magnetoelectric (ME) heterostructure consisting of piezoelectric (AlN) and ferromagnetic magnetic shape memory alloy [FSMA (Ni–Mn–In)] was fabricated over stainless steel (SS) substrate for resistive random access memory application. The Cu/AlN/FSMA/SS metal–insulator–metal based memory cell displays bipolar resistive switching (RS) behavior. The formation of Cu metallic filament at a particular SET voltage leads the memory cell in a low resistance state (LRS) from its pristine high resistance state (HRS). The LRS and HRS are explained well by Ohmic and space charge limited conduction mechanisms, respectively. The fabricated memory cell displays excellent endurance and data retention capability with a high OFF/ON ratio of ∼1.2 × 103. Furthermore, the multifunctionality of the ME heterostructure-based RAM was investigated by tuning the SET voltage with ambiance temperature and external magnetic field remotely. A significant change in the SET voltage could be ascribed to the temperature and magnetic field-induced strain transferred to the AlN piezoelectric layer from the magnetostrictive FSMA (Ni–Mn–In) bottom electrode. The residual Lorentz force explains the remotely tuned LRS and HRS in the transverse magnetic field for multi-bit data storage applications. Moreover, the RS characteristics remain stable even after 800 bending cycles as well as with bending angle (0°–180°). Hence, the present ME heterostructure integrated with flexible SS substrate can be a better choice for highly flexible, low-cost, and multifunctional futuristic RAM applications.

Unraveling the Phase Stability and Physical Property of Modulated Martensite in Ni2Mn1.5In0.5 Alloys by First-Principles Calculations.

Large magnetic field-induced strains can be achieved in modulated martensite for Ni-Mn-In alloys; however, the metastability of the modulated martensite imposes serious constraints on the ability of these alloys to serve as promising sensor and actuator materials. The phase stability, magnetic properties, and electronic structure of the modulated martensite in the Ni2Mn1.5In0.5 alloy are systematically investigated. Results show that the 6M and 5M martensites are metastable and will eventually transform to the NM martensite with the lowest total energy in the Ni2Mn1.5In0.5 alloy. The physical properties of the incommensurate 7M modulated martensite (7M–IC) and nanotwinned 7M martensite () are also calculated. The austenite (A) and phases are ferromagnetic (FM), whereas the 5M, 6M, and NM martensites are ferrimagnetic (FIM), and the FM coexists with the FIM state in the 7M–IC martensite. The calculated electronic structure demonstrates that the splitting of Jahn–Teller effect and the strong Ni–Mn bonding interaction lead to the enhancement of structural stability.