Magnetic Shape Memory Research Articles

Quantum Coherence Control at Temperatures up to 1400 K.

Coherent quantum control at high temperatures is important for expanding the quantum world and is useful for applying quantum technologies to realistic environments. Quantum control of spins in diamond has been demonstrated near 1000 K, with the spins polarized and read out at room temperature and controlled at elevated temperatures by rapid heating and cooling. Further increase of the working temperature is challenging due to fast spin relaxation in comparison with the heating and cooling rates. Here we significantly improve the heating and cooling rates by using reduced graphene oxide as the laser absorber and heat drain and hence realize coherent quantum operation at up to 1400 K, which is higher than the Curie temperatures of all known materials. This work facilitates the use of diamond sensors to study a wide range of magnetic effects in the high-temperature regime, such as thermoremanent magnetism and magnetic shape memory effects.

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

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

Multiferroic Microstructure Created from Invariant Line Constraint

AbstractFerroic materials enable a multitude of emerging applications, and optimum functional properties are achieved when ferromagnetic and ferroelectric properties are coupled to a first‐order ferroelastic transition. In bulk materials, this first‐order transition involves an invariant habit plane, connecting coexisting phases: austenite and martensite. Theory predicts that this plane should converge to a line in thin films, but experimental evidence is missing. Here, the martensitic and magnetic microstructure of a freestanding epitaxial magnetic shape memory film is analyzed. It is shown that the martensite microstructure is determined by an invariant line constraint using lattice parameters of both phases as the only input. This line constraint explains most of the observable features, which differ fundamentally from bulk and constrained films. Furthermore, this finite‐size effect creates a remarkable checkerboard magnetic domain pattern through multiferroic coupling. The findings highlight the decisive role of finite‐size effects in multiferroics.

Optimisation of Active Magnetic Elements in Beam-like Structures—Numerical Modelling Studies

This paper explores integrating advanced materials, including magnetic shape memory alloys, magnetorheological fluids, and classical shape memory alloys, within structural elements to achieve exceptional physical properties. When these materials are integrated within structures—whether as wires, actuators, or dampers—they provide the structures with unique static, dynamic, and damping characteristics not commonly found in nature. This study aimed to evaluate the efficacy of these active materials in enhancing the performance of beam-like structures. This investigation was conducted through a comprehensive numerical analysis, focusing on a composite beam. The study examined the impact of different active elements, their position within the structure, and their influence on key dynamic properties. Additionally, a simplified damage scenario was considered, wherein the adverse effects of structural damage were mitigated through the strategic application of these materials. Numerical simulations were carried out using the finite element method, with custom computational codes developed in MATLAB. The findings of these simulations are presented and discussed in this paper.

Neural network-based nonlinear model predictive control with anti-dead-zone function for magnetic shape memory alloy actuator

Neural network-based nonlinear model predictive control with anti-dead-zone function for magnetic shape memory alloy actuator

Martensitic transformations and magnetic properties of Ni50−xMn37Sn13Fex(x = 0.5, 1, 1.5) melt-spun ribbons

AbstractThe present study investigates the influence of iron (Fe) doping on the martensitic transformation and magnetic properties of Ni50−xMn37Sn13Fex(x = 0.5, 1, 1.5) magnetic shape memory alloys in ribbon form. The ribbons were prepared using arc-melting followed by melt-spinning processes and were characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and vibrating sample magnetometry. Our findings demonstrate that the addition of Fe shifts the martensitic transformation to lower temperatures and increases the Curie point of the austenitic phase, $$T_{c}^{\text A}$$ T c A , leading to an enhanced magnetism in the austenitic phase. Moreover, a significant increase in the magnetization jump $$(\Delta M)$$ ( Δ M ) is observed, from $$ 3.3\;{\text{emu\ g}}^{-1} $$ 3.3 emu\ g - 1 for $$x=1$$ x = 1 to $$17 \, {\text{emu\ g}}^{-1} $$ 17 emu\ g - 1 for $$x=1.5$$ x = 1.5 under a $$50 \, \text {Oe}$$ 50 Oe applied magnetic field. The structural transformations are also found to be sensitive to the external applied magnetic field. The isothermal magnetization curves exhibit the exchange bias effect, which confirms the coexistence of antiferromagnetic and ferromagnetic coupling in the samples. Furthermore, the exchange bias effect increases with the Fe content.

Discrimination of vibrational modes in Ni2MnGa thin films

Vibrational properties in magnetic shape memory alloys are intrinsically connected to the topologies formed due to temperature-dependent breakdown of symmetry. In this sense, herein, we apply Raman spectroscopy in the study of Ni2MnGa films prepared by sputtering on glass and gallium arsenide substrates. Different laser wavelengths probe the Raman active vibrational modes. The non-equilibrium heating mechanisms of the electronic lattice induced by excitation laser power within the thermal penetration depth are used to explain the formation of higher order vibrational modes resulting from phonon-assisted intra-band electronic excitations. The discrimination of the Raman active modes is performed based on calculations carried out within the framework of the density functional theory considering the coexistence of austenite and martensite phases as a function of temperature in films with different crystalline textures and residual stresses. More importantly, this work presents a simple way to discriminate the vibrational modes of the austenite and martensite phases in Ni2MnGa thin films that can be easily applied in the nanodevice development process.

NIR-II light-encoded 4D-printed magnetic shape memory composite for real-time reprogrammable soft actuator

For the intelligent 4D-printed actuators, the excellent performance, including quickly reversible spatial-shape transformation and locking, digital and precise shape manipulation in real-time, and remote actuation in special spaces or harsh environments, is significantly desirable but still challenging. Here, using a UV-curable system containing the shape memory polymer (SMP) and NdFeB particles, namely the magSMP composite, we fabricate a real-time reprogrammable soft actuator via high-resolution Digital Light Processing (DLP)-based 4D printing. The printed structure is composed of an array of physical binary magSMP composite elements (m-bits), analogous to digital bits. Owing to the NdFeB's photothermal effect, each m-bit can be independently and reversibly switched between unlocking or locking states (allowing or prohibiting responsive shape-morphing) in response to the on/off state of NIR-II light. Through projecting NIR-II light patterns for encoding a set of binary instructions onto 4D-printed actuators, the real-time light-programmed deformations are induced precisely under an actuation magnetic field due to the NdFeB's huge coercivity. Thus, the synergistic magnetic and light field-manipulated multimodal deformations of actuators, including mimosa shape changing, grasping, and wire guiding, are achieved. This study shines lights on the fabrication of soft structures of arbitrary sizes and provides their future perspectives in soft robot design.

Effects of element specific Co substitution in Ni-Mn-Ga-Fe and accelerated grain growth during heat treatment

The substitution of small amounts of Co and Fe into Ni-Mn-Ga-based ferromagnetic shape memory alloys (FSMAs) is widely recognized for its ability to finely tune their multifunctional properties. This study investigated the effects of the substitution of each of the parent elements, in amounts of Co = 1, 3, and 5 (at.%), on the crystalline structure transformation temperature, microstructure, and magnetic properties of the nominal alloy Ni50Mn25Ga20Fe5. An induction melting technique was used to fabricate a series of 10 alloys with and without Co-substitution. In addition to determining the evolution of its magnetic and structural characteristics, Co-doping has been found to have an unexpected and beneficial effect on the grain microstructure. The findings of the study revealed that the Ni49Co1Mn25Ga20Fe5 alloy exhibited significant grain growth while demonstrating the mixed 10 M + 14 M martensitic crystal structure at ambient temperature. Separating an oriented grain of 1 × 2 mm enabled the experimental demonstration of magnetic field-induced structural rearrangement through twin-domain motion. Varying the levels of Co-substitution and the specific element being substituted allows tuning between the stabilisation of cubic austenite, modulated martensites (10 M or 14 M), or a non-modulated martensite at ambient temperature. Using standard melting facilities to fabricate large grains of polycrystalline ingots with 10 M + 14 M Co-doped Ni-Mn-Ga-Fe actuating elements offers a practical advantage over growing single crystals.

Magneto-mechanical coupling in ferromagnetic shape memory alloys: Mechanical experimental investigation under magnetic field in NiMnGaCu alloy

Ferromagnetic shape memory alloys attracted increasing interest as multicaloric materials for solid state refrigeration. The most effective field coupling is achieved through the combination of the magnetic and mechanical induction of thermoelastic martensitic transformation. In the present work, we present an experimental investigation on NiMnGaCu polycrystalline cast alloy, by means of an experimental setup for compression tests in isothermal conditions under a longitudinal magnetic field. The setup has been ad hoc designed and developed specifically for this purpose. In this way, we can measure the elastocaloric and magnetocaloric effect at the same time. Moreover, the evolution of the entropy changes ΔS and the functional caloric parameters vs the magnetic field is evaluated. The application of magnetic field seems to act like a supplementary mechanical longitudinal stress. These preliminary results are fundamental to achieve a comprehensive understanding and modeling of coupled multicaloric phenomena.

Compliant Lattice Modulations Enable Anomalous Elasticity in Ni-Mn-Ga Martensite.

High mobility of twin boundaries in modulated martensites of Ni-Mn-Ga-based ferromagnetic shape memory alloys holds a promise for unique magnetomechanical applications. This feature has not been fully understood so far, and in particular, it has yet not been unveiled what makes the lattice mechanics of modulated Ni-Mn-Ga specifically different from other martensitic alloys. Here, results of dedicated laser-ultrasonic measurements on hierarchically twinned five-layer modulated (10M) crystals fill this gap. Using a combination of transient grating spectroscopy and laser-based resonant ultrasound spectroscopy, it is confirmed that there is a shear elastic instability in the lattice, being significantly stronger than in any other martensitic material and also than what the first-principles calculations for Ni-Mn-Ga predict. The experimental results reveal that the instability is directly related to the lattice modulations. A lattice-scale mechanism of dynamic faulting of the modulation sequence that explains this behavior is proposed; this mechanism can explain the extraordinary mobility of twin boundaries in 10M.

A novel scale-bridging method for MSMA linking continuum thermodynamics constitutive formulations to lumped system-level models

This work introduces a novel scale-bridging method between a continuum thermodynamics constitutive model and a lumped system-level model for magnetic shape memory alloys (MSMA). With this method, system models for real-time operations are generated based on virtual experiments using the constitutive model. The proposed method addresses the fact that, while constitutive models for MSMA typically only require small sets of parameters as input, their evaluation is still computationally expensive. System models for control engineering, however, require extensive experimental parameterization, while their evaluation is highly time-efficient. The proposed scale-bridging method has the potential to combine a small parameterization effort and a low computational cost of the real-time system model. Additionally, the constitutive model is utilized to investigate whether it can determine the individual behavior of MSMA samples. This is important since the inherent model parameters, while valid for ideal single crystals, deviate for non-ideal MSMA sample behavior. To this end, the MSMA constitutive model, based on a global variational principle originally proposed by Kiefer et al is supplemented by various extensions, including a more robust algorithmic treatment. A parameter identification procedure is introduced to optimize the constitutive model parameters based on an outer hysteresis curve for a particular load case. By conducting virtual experiments with the constitutive model, data sets are generated to parameterize Preisach hysteresis models as numerical approximations of the constitutive models. The resulting hysteresis models are compared with physical experiments using an MSMA test bench for different load cases. It is shown that the proposed scale-bridging method successfully generates hysteresis models derived from constitutive models. While maintaining accuracy comparable to strictly phenomenological models across various load cases (as validated through physical MSMA test bench experiments), these models require significantly less parameterization effort than classical system models. This translates to faster model creation and broader applicability.

Study of factors affecting the magnetic sensing capability of shape memory alloys for non-destructive evaluation of cracks in concrete: Using response surface methodology (RSM) and artificial neural network (ANN) approaches

Currently, the field of structural health monitoring (SHM) is focused on investigating non-destructive evaluation techniques for the identification of damages in concrete structures. Magnetic sensing has particularly gained attention among the innovative non-destructive evaluation techniques. Recently, the embedded magnetic shape memory alloy (MSMA) wire has been introduced for the evaluation of cracks in concrete components through magnetic sensing techniques while providing reinforcement as well. However, the available research in this regard is very scarce. This study has focused on the analyses of parameters affecting the magnetic sensing capability of embedded MSMA wire for crack detection in concrete beams. The response surface methodology (RSM) and artificial neural network (ANN) models have been used to analyse the magnetic sensing parameters for the first time. The models were trained using the experimental data obtained through literature. The models aimed to predict the alteration in magnetic flux created by a concrete beam that has a 1 mm wide embedded MSMA wire after experiencing a fracture or crack. The results showed that the change in magnetic flux was affected by the position of the wire and the position of the crack with respect to the position of the magnet in the concrete beam. RSM optimisation results showed that maximum change in magnetic flux was obtained when the wire was placed at a depth of 17.5 mm from the top surface of the concrete beam, and a crack was present at an axial distance of 8.50 mm from the permanent magnet. The change in magnetic flux was 9.50 % considering the aforementioned parameters. However, the ANN prediction results showed that the optimal wire and crack position were 10 mm and 1.1 mm, respectively. The results suggested that a larger beam requires a larger diameter of MSMA wire or multiple sensors and magnets for crack detection in concrete beams.

Acoustic emission during approaching the critical point on stress-temperature diagram of martensitic transformation in Ni48Fe20Co5Ga27 (at.%) single crystal

Recently, the existence of martensite-austenite critical point, CP, on the stress-strain curves in the single crystalline Ni–Fe(Co)-Ga ferromagnetic shape memory alloys has been discovered by disappearance of hysteresis. It was also argued that the shear modulus at the CP and in the postcritical phase should be zero. In the present work we continue the investigation of the above new features on the “compression stress-temperature” phase diagram of the martensitic transformation (MT) of Ni48Fe20Co5Ga27 (at.%) single crystals in the vicinity of the CP by acoustic emission (AE). It is found that the AE activity (amount of events and their amplitudes) drastically dropped down by approaching the CP and tended to stabilize in a postcritical region. The above decrease is mainly due to the decrease of the number of large avalanches, while the exponents of the probability distribution of amplitudes and energies remained approximately the same, illustrating no change in the mechanism of acoustic emission events. The coordinates of the CP were estimated to be (340 ± 50) MPa and (327 ± 40) K. The elastic modulus was reduced with increasing temperature from 20 GPa down to 2 GPa in the critical region, whereby a huge total deformation of about 13 % was achieved. The stress-induced MT also shifted as a function of temperature and its slope decreased by about a factor of two upon approaching the CP. All features of the critical state determined have an obvious practical interest, as well as present a solid basis for theoretical understanding of critical and postcritical states in solids.

Spin reorientation in premartensite and austenite Ni–Mn–Ga

The premartensite state of Ni–Mn–Ga magnetic shape memory alloy, sometimes called the martensite precursor state, was studied by careful and detailed measurement of the evolution of magnetization curves of magnetically closed samples to evidence local symmetry breaking. During the heating cycle after the martensite transformation, the magnetization loop slowly transforms from a typical sigmoidal shape, corresponding to the magnetization along the easy axis, to a constricted loop indicative of magnetization along a harder magnetic axis. These changes are explained by a switching of the macroscopic magnetic easy axis from [100] to [110]. Above the premartensite transformation temperature, the magnetic easy axis slowly changes back to [100]. After cooling the sample, starting at the Curie temperature, the process reverses.

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.

Powder-blown laser-based directed energy deposition of (14M) Ni-Mn-Ga magnetic shape memory alloy

Ni-Mn-Ga-based magnetic shape memory (MSM) alloys are renowned for their large magnetic-field-induced strains, making them attractive for compact magnetically controlled actuators requiring high response frequencies and large reversible deformations. In this study, Ni-Mn-Ga alloy samples were deposited using powder-blown laser-based directed energy deposition (DED-LB), employing gas-atomised powder pre-alloyed with excess Mn. The samples were deposited following a systematic experimental design, varying the applied laser power and employing two melting strategies: unidirectional and bidirectional. The results demonstrate the feasibility of achieving high relative densities (>97.5 %) in multi-layered Ni-Mn-Ga samples through DED-LB. All as-deposited samples exhibited a consistent 0.7–0.9 at% Mn loss in comparison to the powder feedstock, thus showing that the Mn overdosing requirements for DED-LB differ from those in laser powder bed fusion. Both as-deposited and heat-treated samples exhibited seven-layered modulated (14 M) martensite structures at ambient temperature. In contrast, the heat-treated samples also exhibited fully reversible martensite transformation at around 66 ºC and a Curie temperature at around 94 ºC. Distinct microstructural characteristics were observed based on the melting strategy, with bidirectional melting promoting the formation of large columnar grains with a strong <100> texture approximately along the build direction. This study highlights the potential of DED-LB processes in manufacturing relatively large (mm to cm scale) functional Ni-Mn-Ga actuators and contributes to the ongoing efforts in laser additive manufacturing of functional materials.

High-Throughput Screening of All-d-Metal Heusler Alloys for Magnetocaloric Applications.

Due to their versatile composition and customizable properties, A2BC Heusler alloys have found applications in magnetic refrigeration, magnetic shape memory effects, permanent magnets, and spintronic devices. The discovery of all-d-metal Heusler alloys with improved mechanical properties compared to those containing main group elements presents an opportunity to engineer Heusler alloys for energy-related applications. Using high-throughput density-functional theory calculations, we screened magnetic all-d-metal Heusler compounds and identified 686 (meta)stable compounds. Our detailed analysis revealed that the inverse Heusler structure is preferred when the electronegativity difference between the A and B/C atoms is small, contrary to conventional Heusler alloys. Additionally, our calculations of Pugh ratios and Cauchy pressures demonstrated that ductile and metallic bonding are widespread in all-d-metal Heuslers, supporting their enhanced mechanical behavior. We identified 49 compounds with a double-well energy surface based on Bain path calculations and magnetic ground states, indicating their potential as candidates for magnetocaloric and shape memory applications. Furthermore, by calculating the free energies, we propose that 11 compounds exhibit structural phase transitions and suggest isostructural substitutions to enhance the magnetocaloric effect.

Cu- and Fe-Doped Ni-Mn-Sn Shape Memory Alloys with Enhanced Mechanical and Magnetocaloric Properties.

Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) are multifunctional materials that are promising for solid-state refrigeration applications based on the magnetocaloric effect (MCE) and elastocaloric effect (eCE). However, a combination of excellent multi-caloric properties, suitable operating temperatures, and mechanical properties cannot be well achieved in these materials, posing a challenge for their practical application. In this work, we systematically study the phase transformations and magnetic properties of Ni50-xMn38Sn12Cux (x = 0, 2, 3, 4, 5, and 6) and Ni50-yMn38Sn12Fey (y = 0, 1, 2, 3, 4, and 5) alloys, and the magnetic-structural phase diagrams of these alloy systems are reported. The influences of the fourth-element doping on the phase transitions and magnetic properties of the alloys are elucidated by first-principles calculations. This work demonstrates that the fourth-element doping of Ni-Mn-Sn-based FSMA is effective in developing multicaloric refrigerants for practical solid-state refrigeration.

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.