Magnetic Shape Memory Research Articles

Large elastocaloric effect in as-cast Ni-Mn-Sn-Fe ferromagnetic shape memory alloys

The Ni-Mn-Sn ferromagnetic shape memory alloys exhibit excellent both magnetic field-induced magnetocaloric effect and uniaxial stress-induced elastocaloric effect. However, the intrinsic brittleness and narrow refrigeration temperature regions hinder their practical applications in elastocaloric and magnetocaloric as well other fields. In this work, the as-cast Ni44-xFexMn46Sn10 (x = 1, 2, 3) alloys are prepared directly by cooling solidification. The as-cast alloys improve the mechanical properties and broaden the martensitic transformation temperature region due to the presence of dendrites. The dendrites prevent cracking formation and propagation along the grain boundaries, and the addition of Fe-atoms enriched in the interdendritic region further optimizes the mechanical performance. In addition, the as-cast Ni41Fe3Mn46Sn10 alloy exhibits a large adiabatic temperature variation up to −10.3 K at a moderate stress of 350 MPa. Accordingly, direct cooling solidification of as-cast alloys could be a novel and feasible method for studying elastocaloric cooling technology.

Elastocaloric Effect in Aged Single Crystals of Ni54Fe19Ga27 Ferromagnetic Shape Memory Alloy

In the present study, the effect of γ′-phase dispersed particles on both the L21(B2)-10M/14M-L10 martensitic transformations and the elastocaloric effect in aged Ni54Fe19Ga27 single crystals oriented along the [001]-direction was investigated. It was experimentally shown that aging strongly affects the elastocaloric properties of these crystals. The precipitation of semi-coherent γ′-phase particles up to 500 nm in size in the crystals aged at 773 K for 1 h leads to a 1.4 times increase in the operating temperature range of the elastocaloric effect up to ΔTSE = 270 K as compared with the initial as-grown crystals (ΔTSE = 197 K). The adiabatic cooling values ΔTad are similar for the as-grown crystals ΔTad = 10.9 (±0.5) K and crystals aged at 773 K ΔTad = 11.1 (±0.5) K. The crystals containing incoherent γ′-phase particles sized 5–35 μm (after aging at 1373 K for 0.5 h) possess an operating temperature range of ΔTSE = 255 K with slightly smaller adiabatic cooling ΔTad below 9.7 (±0.5) K. The aged [001]-oriented Ni54Fe19Ga27 single crystals demonstrate high cyclic stability: the number of cycles does not influence the adiabatic cooling values and parameters of loading/unloading curves regardless of the particle size. The ways to improve the elastocaloric cooling parameters and stability of the elastocaloric effect by means of dispersed particles in the NiFeGa ferromagnetic shape memory alloy were discussed.

Magnetic properties and possible martensitic transformation in equiatomic quaternary Heusler alloy CoMnNiSn

Equiatomic quaternary Heusler alloy CoMnNiSn has been synthesized in both bulk and ribbon form to explain the contradictions in the magnetic properties and possible martensitic transformation between different literature. The structure, magnetic properties and electronic structure of CoMnNiSn were investigated both theoretically and experimentally. A cubic Heusler phase can be identified in the XRD patterns. A small amount of secondary phase is observed in bulk CoMnNiSn while it is eliminated in the melt-spun ribbons. The saturation magnetization Ms at 5 K of bulk and ribbon CoMnNiSn are 4.85 μB/f.u. and 4.76 μB/f.u., respectively. This and also the calculation results suggest that ferromagnetic ground state has been established in CoMnNiSn samples. There is no trace of martensitic transformation in CoMnNiSn bulk and ribbon samples. The L21B atomic disorder can be responsible for this, which comes from the random occupation of Co/Ni at A, C sites in the cubic lattice of CoMnNiSn and has a higher stability comparing with the ordered Y-type structure. This suppression effect is further explained by the weakening of the Jahn-Teller effect in the austenite DOS of L21B type CoMnNiSn. All this calls for more attention to the effects of atomic disorder in the design of magnetic shape memory alloys in equiatomic quaternary Heusler alloys.

Nanotwinned (inter)martensite transformation interfaces in Ni50Mn25Ga20Fe5 magnetic shape memory single crystal foil

Using common and high resolution transmission electron microscopy (TEM), we study the magnetic and crystal phase structures as well as their evolution in Ni50Mn25Ga20Fe5 magnetic shape memory material with high Curie point. The particular alloying by Fe and changing thickness of the TEM foil enable us to observe all martensitic phases known in Ni-Mn-Ga Heusler alloy system and their respective transitions simultaneously. Starting from cubic austenite at about 10 nm foil thickness, the structure evolves via peculiar interleaved stripes of austenite and five-layered modulated 10M martensite to pure 10M phase with a low density of stacking faults at 40 nm thickness. With further increasing thickness, the 10M phase transforms gradually to seven-layered modulated 14M martensite with an increased density of stacking faults. Finally, the non-modulated tetragonal NM phase appears within the 14M phase by detwinning of nanotwins forming the modulated phases. High resolution TEM further confirms that nanotwinning and stacking faults are inherent structure features tightly connected with the lattice modulation and intermartensite transformations. Overall, the evolution of average lattice shows the same general trend, an increasing simple shear with (11¯0) shuffling plane, across the whole phase sequence. Additionally, we found large local variation of lattice parameters in all phases, which is is ascribed to strong lattice softening in the vicinity of the martensitic transformation and high density of stacking faults in 14M martensite lattice.

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.

Theoretical formulism analyzing damping nature of the ferromagnetic shape memory alloy

The behavior of acoustic stress waves propagated through Ferromagnetic Shape Memory Alloy (FSMA) is formulated theoretically for analyzing their energy-absorbing capability and is validated with experimental measurements. In the experiment, piezostack actuator transfers the series of asymmetric acoustic pulses through Ni48Mn32Ga20 single crystal to induce twin boundary motion. Thereby suppressing the vibration along the sample and are observed using a PZT sensor. Based on these experimental conditions, one dimensional wave function is theoretically derived to numerically compute the damping behavior of Ni48Mn32Ga20 sample. These analyses can be utilized to design a highly efficient and cost-effective damper using an FSMA sample.

Magnetic-induced dual-function tunable THz polarization conversion metamaterial based on Ni-Mn-Sn shape memory alloy films

Due to the improvement in miniaturization and practicability of polarization conversion devices, the terahertz polarization control technology has been paid more and more attention. Nevertheless, a critical factor in restricting its development is short of dynamic and multifunctional materials. Ferromagnetic shape memory alloys (FSMAs) provide a novelty solution for tunable metamaterials because of their excellent recovery deformation, non-contact control, and fast response. Here, a new magnetic-induced tunable THz metamaterial is proposed, composed of Ni-Mn-Sn FSMAs resonator in strip structure, polyimide dielectric, and metal copper substrate. Numerical results reveal that the polarization converter can realize any in a broad band between 1.04 and 1.96 THz by applying different magnetic fields to adjust the elastic deformation of Ni-Mn-Sn. Notably, the device can also realize line circularly polarized light conversion in the range of 0.87–0.92 THz and 2.07–2.12 THz. Compared to the current state-of-the-art double functional polarization converter, the THz converter proposed in this work offers benefits in many respects, including the 61.3% relative bandwidth and high conversion efficiency. Our study provides an excellent strategy to develop actively tunable and multifunctional THz compact devices.

Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains.

Magnetic force microscopy (MFM) enables mapping local magnetic fields across a sample surface with nanoscale resolution. To perform MFM, an atomic force microscopy (AFM) probe whose tip has been magnetized vertically (i.e., perpendicular to the probe cantilever) is oscillated at a fixed height above the sample surface. The resultant shifts in the oscillation phase or frequency, which are proportional to the magnitude and sign of the vertical magnetic force gradient at each pixel location, are then tracked and mapped. Although the spatial resolution and sensitivity of the technique increases with decreasing lift height above the surface, this seemingly straightforward path to improved MFM images is complicated by considerations such as minimizing topographical artifacts due to shorter range van der Waals forces, increasing the oscillation amplitude to further improve sensitivity, and the presence of surface contaminants (in particular water due to humidity under ambient conditions). In addition, due to the orientation of the probe's magnetic dipole moment, MFM is intrinsically more sensitive to samples with an out-of-plane magnetization vector. Here, high-resolution topographical and magnetic phase images of single and bicomponent nanomagnet artificial spin-ice (ASI) arrays obtained in an inert (argon) atmosphere glovebox with <0.1 ppm O2 and H2O are reported. Optimization of lift height and drive amplitude for high resolution and sensitivity while simultaneously avoiding the introduction of topographical artifacts is discussed, and detection of the stray magnetic fields emanating from either end of the nanoscale bar magnets (~250 nm long and <100 nm wide) aligned in the plane of the ASI sample surface is shown. Likewise, using the example of a Ni-Mn-Ga magnetic shape memory alloy (MSMA), MFM is demonstrated in an inert atmosphere with magnetic phase sensitivity capable of resolving a series of adjacent magnetic domains each ~200 nm wide.

Introducing cobalt nickel aluminum ferromagnetic shape memory alloy for endodontic file manufacturing

Since the introduction of nickel titanium (NiTi) to the field of endodontics, it paved the way for fast and reliable root canal instrumentation. Rotary instruments are solely manufactured from NiTi alloy, due to its favorable mechanical and physical properties such as flexibility and cutting efficiency. The main problem with rotary NiTi instruments is their high fatigue susceptibility, and the unexpected incident of instrument separation inside the root canal, complicating the case even further and might even doom the tooth for extraction it the fractured fragment was unretrievable with the presence of peri-apical pathology. Many attempts were made to enhance the physical and mechanical properties of NiTi alloy through modification to the manufacturing process or with different heat treatment or even adding alloying elements to it. However, there has never been an attempt to replace the whole alloy. Cobalt Nickel Aluminum (Co-Ni-Al) alloy is a ferromagnetic shape memory (FMSM) alloy, possessing favorable mechanical and physical properties making it a good candidate to replace NiTi in the manufacturing of rotary instruments. With its main advantage being the ability to be retrieved with magnetic pulses after being separated.

Investigation of the complex magnetic behavior of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloy at low temperatures

The magnetic properties, martensitic transformation characteristics, the magnetic field-induced transformation characteristics, and super spin-glass behaviour at low temperature of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloys (MSMAs) were investigated under various magnetic field levels over temperature intervals from 400 K to 10 K. We observe a small magnetization difference during the martensitic transition evidenced with a visible thermal hysteresis. To investigate the magnetic field induced phase fraction, the minimum magnetic field required to start and complete the magnetostructural phase transition is computed. Super-spin glass features in magnetic data are observed that interacting magnetic clusters are frozen below a critical temperature. Magnetization is computed as a function of temperature at various constant fields using molecular field theory. The critical exponent, β is deduced for the temperature-induced magnetization, which indicates that the MSMA exhibited ferromagnetic ordering during field-cooling and on heating an antiferromagnetic ordering at low temperatures and in low applied magnetic fields. These observations are consistent within the framework of an Ising or Heisenberg model.

The effect of Tb substitution for Ni on microstructure, martensitic transformation and cyclic stability of elastocaloric effect in Ni–Mn–Sn magnetic shape memory alloys

Cyclic stability of elastocaloric effect is the key factor that restricts the elastocaloric cooling application of Ni–Mn–Sn alloys fabricated by the conventional melting technique. Element doping is an effective way to enhance the performance of materials. In this work, the effect of Tb substitution for Ni on martensitic transformation (MT) temperature, microstructure, mechanical properties and cyclic stability of elastocaloric effect in the Ni43.5–xTbxMn45.5Sn11 (x = 0, 0.6, 1.2 and 1.8) magnetic shape memory alloys has been investigated. MT temperatures increase with increasing x from 0 to 1.2 and then decrease with further increasing x to 1.8. The substitution of Tb for Ni introduces γ phase (Tb-rich second phase in Tb-doping alloys). The volume fraction of γ phase increases with increasing Tb content and thus the mechanical properties and the cyclic stability of elastocaloric effect increase with the increase of Tb content. Among these alloys, Ni42.3Tb1.2Mn45.5Sn11 alloy shows a large adiabatic temperature change of 10.0 K induced by applying the uniaxial stress of 550 MPa. In addition, a constant temperature change of 6.5 K shows no apparent degradation under the compressive stress of 350 MPa during 1000 cycles for this alloy. The excellent elastocaloric properties make this alloy a promising candidate for the room-temperature elastocaloric cooling application. The underlying mechanism of the enhanced cyclability of elastocaloric effect and mechanical properties is also revealed.

Synthesis and characterisation of Fe-substituted Ni50Mn25Fe Ga25- single crystals—Development of the phase transformations with Fe content

Despite promising initial properties, the industrial applicability of magnetic shape memory alloys of the Ni-Mn-Ga family is distinctly limited by the temperature range it can operate in. Here we investigate the effects of minor substitutions of Fe for Ga on the thermodynamic, structural, and magnetic properties of Ni50Mn25FexGa25-x (3.0 < x < 7.5). Single crystals are essential for most intended applications, the studied compositions were prepared in single crystalline form. With increasing iron content, the melting point of the alloy decreases slightly from 1407(2) to 1394(2) K, while the structural B2’→L21 ordering transition increases in temperature from 1066(2) to 1082(4) K. Magnetisation measurements find that both the Curie temperature and the martensitic transformation temperature increase approximately linearly with Fe concentration, with Curie temperature increasing from 398(1) to 427(2) K, and martensitic transformation temperature increasing from 274(1) to 372(1) K when going from x = 3.0–7.5. The martensitic transformations above room temperature were confirmed by temperature-dependent single-crystal X-ray diffraction. These observations are compared with polycrystalline materials of the same series and support results of the previous studies. The shrinking gap between Curie and martensitic transformation temperatures, as well as the reduction in the low temperature saturated moment from 3.52(2) to 2.78(3) µB/f.u. make this substitution less industrially attractive but provide essential structural and property evolution details needed to improve and tune theoretical modelling of this important material family.

Dependence of martensite transformation temperature on magnetic field in Ni2MnGa and Ni2MnGa0.95In0.05 single crystals

The shift of martensite transformation temperatures with magnetic field is an essential parameter for magnetic shape memory effect as well as for magnetocalorics. We compare the dependence of martensite transformation temperature on magnetic field in Ni2MnGa and Ni2MnGa0.95In0.05 single crystals. Choosing the stoichiometric and isoelectronic compound enables to observe the effect of In alloying free from the influence of off-stoichiometry. The martensite start temperature, Ms, decreases several kelvins in low magnetic fields (< 1 T). In high field (> 2 T), Ms increases with the magnetic field and the Ms(H) dependence is about linear with the slope of 0.26 K/T (Ni2MnGa) and 0.36 K/T (Ni2MnGa0.95In0.05). Modest 1.25 at% indium alloying decreases not only transformation temperature Ms by about 100 K but also considerably decreases the latent heat of martensite transformation from 1.99 kJ/kg (Ni2MnGa) to 0.29 kJ/kg (Ni2MnGa0.95In0.05) determined from Clausius-Clapeyron equation. The latent heat of premartensitic transformation also decreases, approximately five times.

The nature of the metamagnetic transition in Heusler alloy Ni44.9Mn43In12.1 studied for magnetic refrigeration application

The nature of the phases, phase transitions, and their magnetic characteristics all play an essential role in the performance of Ni-Mn-In Heusler alloys, both as magnetic shape memory and giant magnetocaloric effect (MCE) materials. The details of the structural and magnetic transformations in Ni 44.9 Mn 43 In 12.1 Heusler alloy are reported in this work, using synchrotron and neutron diffraction and AC-SQUID susceptibility results. Of special interest is the affirmation of an antiferromagnetic (AFM) phase and the exclusion of a spin-glass state as the cause of the observed drop in magnetization upon cooling. This is of critical importance for magnetocaloric applications because of the dominant contribution to MCE of the magnetic entropy change upon phase transformation. • The magnetic and crystallographic nature of Ni 44.9 Mn 43 In 12.1 , were studied using synchrotron and neutron diffraction and AC-SQUID. • Cooling below 304 K results in ferromagnetic to antiferromagnetic transition; critically important for the magnetocaloric effect. • The crystallographic and magnetic transformations from austenite to martensite and from ferromagnetic to antiferromagnetic, coincide. • The hysteresis of the crystallographic transition is narrow, an advantage for MCE and other applications.

Thermo-magnetic loading effects on high-frequency dynamic behaviour of magnetic shape memory alloys

This paper theoretically studies the thermo-magnetic loading effects on the long-term (>100 s, reaching the steady state) high-frequency (>100 Hz) dynamic behaviour of magnetic shape memory alloys actuated by cyclic magnetic fields. The material's dynamic behaviour at different levels of ambient heat-transfer, ambient temperature, applied magnetic field frequency and amplitude are simulated by a dynamic model incorporating both magnetic-field-induced martensite reorientation and temperature-driven martensitic phase transformation. Analytical expressions of the material's long-term steady-state behaviour (i.e., stable strain amplitude and temperature) as a function of ambient thermal conditions and magnetic loading conditions are further derived. It is found from model simulations and analytical calculations that weak ambient heat-transfer, high ambient temperature, and high magnetic field amplitude (to trigger martensite reorientation) lead to large net heat generation from dissipative martensite reorientation and thus increase material's stable temperature, which results in reduced twinning stress and increased stable strain amplitude. It is also found that the material's stable temperature can reach the characteristic phase transformation temperature triggering the martensite-to-austenite transformation. In this case, weaker ambient heat transfer, higher ambient temperature and higher magnetic field frequency result in larger heat generation rate accelerating the martensite-to-austenite transformation. Therefore, less martensite remains in the material and the material's stable strain amplitude becomes smaller.

Design and Control of Magnetic Shape Memory Alloy Actuators.

This paper presents research on the application of magnetic shape memory alloys (MSMAs) in actuator design. MSMAs are a relatively new group of so-called smart materials that are distinguished by repeatable strains up to 6% and dynamics much better than that of thermally activated shape memory alloys (SMAs). The shape change mechanism in MSMAs is based on the rearrangement of martensite cells in the presence of an external magnetic field. In the first part of the article a review of the current state of MSMA actuator design is presented, followed by a description of the design, modelling and control of a newly proposed actuator. The developed actuator works with MSMA samples of 3 × 10 × 32 mm3, guaranteeing an available operating range of up to 1 mm, despite its great deformation range and dynamics. In the paper its dynamics model is proposed and its transfer function is derived. Moreover, the generalised Prandtl-Ishlinskii model of MSMA-actuator hysteresis is proposed. This model is then inverted and used in the control system for hysteresis compensation. A special test stand was designed and built to test the MSMA actuator with compensation. The step responses are recorded, showing that the compensated MSMA actuator exhibits the positioning accuracy as ±2 µm. As a result, the authors decided to apply a control system based on an inverse hysteresis model. The paper concludes with a summary of the research results, with theoretical analysis compared with the registered actuator characteristics.

A micromechanical constitutive model for porous ferromagnetic shape memory alloys considering magneto-thermo-mechanical coupling

In this work, a three-phase constitutive model describing the magneto-thermo-mechanical behaviors of porous Ferromagnetic Shape Memory Alloys (FSMAs) is established through a combination of micromechanical and thermodynamic theories. The kinetic equation is obtained in accordance with the thermodynamic driving force caused by the reduction of Gibb’s free energy of porous FSMAs. The thermodynamic driving force in combination with the corresponding resistance is used to establish the balance equation for calculating the volume fractions of martensitic variants under the action of different given magnetic fields, stresses and temperatures. Good agreement between the theoretical prediction of dense FSMA models and published experimental data is observed. The mechanical behaviors of porous FSMAs under magneto-thermo-mechanical coupling with different porosities and initial conditions are then discussed, which will provide a reliable theoretical basis for the future research of these functional materials as sensors or actuators.

On the power and efficiency of Ni2MnGa magnetic shape memory alloy power harvesters

The martensite variant reorientation in Ni2MnGa magnetic shape memory alloys (MSMAs) causes a change in their bulk magnetization, that can be harvested into useful voltage/power by means of a pick-up coil. The coil may be placed directly surrounding an MSMA element or to the side of the MSMA element wrapped around a magnetic core. This paper reports new power harvesting data generated with a bi-axial magnetic field and a surrounding coil and full strain field data for an MSMA subject to load similar to what is seen during power harvesting, then compares the performance of MSMA-based power harvesters with different designs to determine which give the best output. For this comparison, we provide a framework for evaluating the performance of MSMA-based power harvesters reported in the literature. This framework involves normalizing the results to the design characteristics of the respective harvesters, i.e. number of turns of the pickup coil, cross-sectional area of the pickup coil, frequency of excitation, and sample size, to allow for a direct comparison of power harvesters’ output. Results show that power harvesting with the bi-axial field and a surrounding coil does not generate as much power as previously thought. The strain maps reveal the potential for perpendicular twin boundaries that block each other’s motion limiting variant reorientation and correspondingly the harvester’s power output. The paper concludes that the largest change in magnetic flux density, which is the driver for power harvesting, occurs in the side coil setup with an optimized magnetic circuit and it recommends using this configuration for future MSMA-based power harvester designs for maximum power output.

Modeling and experimental investigation of energy harvesting based on magnetic shape memory alloys

Modeling and experimental investigation of energy harvesting based on magnetic shape memory alloys

Simultaneous improvement of magnetic-field-induced working temperature and mechanical properties in Ni–Mn–In shape memory alloy

Ni–Mn–In magnetic shape memory alloys, which can be stimulated by an external magnetic field, exhibit a fast response and have aroused wide attention in the field of electro-mechanical actuators. However, the low working temperature and the inherent brittleness severely limit their application scenarios. Here, an effective strategy is proposed to improve the magnetic-field-induced working temperature and mechanical properties in Ni–Mn–In shape memory alloys. We predict that the Ni16Mn12In4 alloy with Pt doping can solve the problems simultaneously through a comprehensive first-principles study. The calculations show that Pt occupying Ni sites can increase the martensitic temperature (TM) and Curie temperature (TC) simultaneously. TM and TC of Ni14Mn12In4Pt2 are predicted to be as high as 440 and 476 K, respectively. This is mainly due to the increased phase stability of the martensite and Pt–Mn bonds having stronger ferromagnetic exchange effects than Ni–Mn bonds after Pt doping. Moreover, according to the increase of B/G and v after Pt doping, it can be concluded that the mechanical properties of the alloy have been improved.