Metamagnetic Shape Memory Alloys Research Articles

Impact of magnetic, atomic and microstructural ordering on the magnetocaloric performance of powdered NiCoMnSn metamagnetic shape memory ribbons

Co-doped NiMnSn Heusler-type metamagnetic shape memory alloys (MMSMAs) are promising materials for the next-generation solid-state refrigeration systems due to their excellent magnetocaloric performance around the martensitic transformation, which is easily tuneable by slight changes in the alloy composition. An improvement in the thermal efficiency of active magnetic regenerator devices, a key element in magnetocaloric cooling systems, arises by obtaining powdered magnetocaloric alloys that meet technical requirements for their implementation as a feedstock material in the additive manufacturing of 3D-printed heat exchangers. In the present work, powders of Mn-rich NiCoMnSn Heusler-type MMSMAs were obtained from their ribbon form avoiding or minimizing residual stresses, the number of defects and disorder in the crystal lattice and microstructure. Since atomic order and crystallographic structure are crucial in the transformation and magnetic properties of these alloys, a complementary structural analysis of the powders after different heat treatments was performed by powder neutron diffraction. The results show that the cubic austenitic phase of the non-heat-treated melt-spun powder exhibits a highly stressed structure, which leads to an incomplete martensitic transformation and, therefore, to the coexistence of martensitic and austenitic phases at low temperatures. The magnetic structure of the austenite phase was also determined by neutron powder diffraction, obtaining a ferromagnetic coupling between 4a and 4b Wyckoff positions in the samples analysed. It was found that a heat treatment facilitates the martensitic transformation and enables the formation of a pure martensitic phase.The observed changes in the magnetocaloric performance of the powders have been understood in terms of the differently stressed structures and their impact on the martensitic transformation. A fully completed structural transformation leads to a significant increase of the magnetisation change across the martensitic transformation and, consequently, to high values of both a magnetic field induced isothermal entropy change and refrigeration capacity.

Transformation behavior and inverse magnetocaloric effect in Ni45Co5Mn36.7In13.3-xGex melt-spun ribbons

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni45Co5Mn36.7In13.3-xGex (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ0H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ0H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form.

Monitoring structural transformations in metamagnetic shape memory alloys by non-contact GMI technology

Different applications based on metamagnetic shape memory alloy (MSMA) require monitoring the evolution of the martensitic transformation (MT) to optimize the actuation mechanism. To avoid interaction with the active material, a non-contact technique would be ideal. Nevertheless, non-contact detection involves complex methods like diffraction, optical analysis, or electromagnetic technology. The present work demonstrates that the MT can be monitored without interaction with the active material using a low-cost technology based on the Giant Magnetoimpedance (GMI) effect. The GMI sensor is based on a (CoFe)SiB soft magnetic wire submitted to an alternating current and whose second harmonic voltage variation allows to detect changes in the strength of the stray magnetic fields linked to the metamagnetic phase transition. The sensor has been tested using the MT of a NiMnInCo MSMA. A specific application for environmental temperature control using the non-contact GMI sensor is proposed.

Shape memory and elastocaloric properties of melt-spun NiMn-based Heusler alloys

In the present work, towards further development of NiMn-based Heusler-type elastocaloric alloys a series of melt-spun ribbons have been prepared from three multicomponent Ni-Mn-Sn-based metamagnetic shape memory alloys (MetaMSMAs) and two multicomponent Ni-Mn-Ga-based ferromagnetic shape memory alloys (FSMAs). Their thermoelastic martensitic transformation (TMT), crystal structure and thermomechanical properties have been studied in detail. Whereas FSMAs ribbons showed a conventional stress-strain behavior at TMT and conventional elastocaloric effect (eCE), MetaMSMAs ribbons, in turn, exhibited highly pronounced inverse stress-strain and inverse eCE characteristics at TMT. The abnormal thermomechanical behavior of the MetaMSMA ribbons is produced by the presence of significant internal stresses due to appropriate amount of quenched-in defects resulting from the rapid solidification of melt-spun alloys. The results of the present study can serve as a guide for the design of new eCE-efficient materials in the form of ribbon.

Pd2 MnGa Metamagnetic Shape Memory Alloy with Small Energy Loss.

Metamagnetic shape memory alloys (MMSMAs) are attractive functional materials owing to their unique properties such as magnetostrain, magnetoresistance, and the magnetocaloric effect caused by magnetic-field-induced transitions. However, the energy loss during the martensitic transformation, that is, the dissipation energy, Edis , is sometimes large for these alloys, which limits their applications. In this paper, a new Pd2 MnGa Heusler-type MMSMA with an extremely small Edis and hysteresis is reported. The microstructures, crystal structures, magnetic properties, martensitic transformations, and magnetic-field-induced strain of aged Pd2 MnGa alloys are investigated. A martensitic transformation from L21 to 10M structures is seen at 127.4K with a small thermal hysteresis of 1.3K. The reverse martensitic transformation is induced by applying a magnetic field with a small Edis (=0.3Jmol-1 only) and a small magnetic-field hysteresis (=7kOe) at 120K. The low values of Edis and the hysteresis may be attributed to good lattice compatibility in the martensitic transformation. A large magnetic-field-induced strain of 0.26% is recorded, indicating the proposed MMSMA's potential as an actuator. The Pd2 MnGa alloy with low values of Edis and hysteresis may enable new possibilities for high-efficiencyMMSMAs.

Enhanced elastocaloric effect and mechanical properties of Gd-doped Ni-Co-Mn-Ti-Gd metamagnetic shape memory alloys

Improving elastocaloric effect (eCE) and mechanical properties is the key to developing high-performance eCE cooling materials. In this paper, the metamagnetic shape memory alloys Ni35.5Co13.5Mn35Ti15-xGdx (x = 0–0.9) were successfully prepared by arc melting method, and the effects of Gd substitution for Ti on the martensitic transformation (MT) temperature, phase composition, microstructure, eCE and mechanical properties of the alloys were systematically investigated. With the introduction of Gd elements, the transformation temperature shifts to a low temperature, and the mechanical properties of the alloy are also enhanced. The fracture strength increased from 980 MPa (x = 0) to 1142 MPa (x = 0.9). At room temperature (RT), a large adiabatic temperature change of + 13.5 K/− 12.7 K is obtained after loading/unloading, and a constant temperature change of + 5.6 K/− 5.5 K is obtained without apparent degradation under the compressive stress of 400 MPa during 61 cycles for all-d metal Heusler Ni36.5Co13.5Mn35Ti14.9Gd0.1 alloy. The adiabatic temperature change of 13.5 K exceeds the elastocaloric temperature change of most NiMn-based alloys available at present, and the mechanical properties of Ni-Co-Mn-Ti-Gd alloy are at a high level among the NiMn-based alloys. The precipitation of the Gd-rich second phase along the grain boundaries is intrinsically responsible for the improved mechanical properties.

Improvement of mechanical properties and elastocaloric effect in Ag doped Ni-Mn-In magnetic shape memory alloys

Mechanical properties and elastocaloric effect are the most important parameters of Ni-Mn-In shape memory alloys in the refrigeration field. This paper mainly studies the influence of Ag doping and different preparation methods on the mechanical properties and elastocaloric effect of the alloys. The doping of Ag element not only increases the martensitic transformation temperatures and reduces the critical phase transformation stress, but also improves the mechanical properties and elastocaloric effect of the alloys. The adiabatic temperature change (ΔTad) of Ni50Mn34In15.5Ag0.5 prepared by arc melting was − 7 K at 4% strain, and the alloy fractured after 69 cycles with 3% strain. Furthermore, Ni50Mn34In15.5Ag0.5 powders prepared by gas-atomization were used by SPS sintered to obtain 10 µm grains alloys. This preparation method enables the fracture stress and fracture strain to reach 1625.8 MPa and 17.1%, respectively. At the same time it remains stable after 300 cycles with 6.5% strain, indicating the significant improvement of mechanical properties and cyclic stability in Ni-Mn-In metamagnetic shape memory alloy.

Uncovering the origin of physical properties associated with magneto-structural transition of Ni-Mn-In-X alloys by ab initio methods

Ni-Mn-In metamagnetic shape memory alloys exhibit magneto-structural coupling features during martensitic transformation. In the present work, the composition-dependent crystal structure, phase stability, elastic and magnetic properties of the off-stoichiometric Ni2Mn1.5In0.5 alloy doped with the fourth element X (X = Co, Fe, and Cu) are investigated by using the ab initio calculations. Results show that Co prefers to occupy the Ni sublattice, Fe or Cu takes the Mn site. Doping X constituent reduces the stability of the austenite (A) and non-modulated (NM) martensite. For doped Co, martensitic transformation can occur at 0 ≤ x ≤ 0.75, and there exists a magneto-structural coupling characteristic with the Co range in 0 ≤ x ≤ 0.25. For the case of Fe or Cu doping, the martensitic transformation is accompanied by the change of magnetism. The results of elastic properties indicate that the plasticity and toughness increase significantly with Fe or Cu doping and decrease with Co doping. Furthermore, the origin of the physical properties associated with the magneto-structural coupling transition is explained in terms of the electronic density of states.

Complete and reversible magnetostructural transition driven by low magnetic field in multiferroic NiCoMnIn alloys

Magnetic-field-induced first-order magnetostructural transition (MFI-FOMST) brings about an ample variety of intriguing magnetoresponsive effects including magnetocaloric effect, magnetoresistance and magnetostrain. Metamagnetic shape memory alloys (MSMAs) exhibit MFI-FOMST and thus giant magnetoresponsive effects, but the critical field for complete and reversible MFI-FOMST, (μ0∆H)min, is too high (usually >5 T), which has been a longstanding bottleneck for practical applications. Here, we successfully achieved complete and reversible MFI-FOMST under a low field of 1.5 T, which can be generated by permanent magnets, in a prototype MSMA. The significant reduction of (μ0∆H)min is realized by simultaneously enlarging the distance between Curie transition and magnetostructural transition and manipulating the geometric compatibility between the transforming phases. The low (μ0∆H)min provides a great opportunity for attaining low-field-induced large reversible magnetoresponsive effects. For instance, a large reversible magnetocaloric effect is achieved under 1.5 T. Our realization of low-field-induced complete and reversible first-order magnetostructural transition may push a significant step forward towards the practical use of MSMAs. This work is instructive for developing novel magnetic materials with low-field-actuated first-order phase transition for applications as magnetic actuators, magnetoresistors and solid-state refrigerants.

Multicaloric effect in Ni–Mn–Sn metamagnetic shape memory alloys by laser powder bed fusion

Metamagnetic shape memory alloys with giant caloric effects and sophisticated geometries are promising candidates for solid-state refrigeration. Additive manufacturing (AM) overcomes the machining difficulties and may provide the geometric freedom. Whereas the metallurgical defects in AM limits their applications, and the multicaloric effects of AM metamagnetic shape memory alloys have been poorly understood. Here, Ni 45 Mn 44 Sn 11 metamagnetic shape memory alloys are prepared via laser powder bed fusion ( L -PBF). A magnetic entropy change of 10.2 J kg −1 K −1 and adiabatic temperature change of 0.8 K is achieved under the external field change of 5 T and 1.5 T, respectively. An improved relative density of ∼99.5% and high compressive strength of 519 MPa is achieved. These result from the defects mitigation which shows homogeneous grain structure/composition and crack healing during rapid printing and subsequent annealing. Particularly, we have proposed a multicaloric approach of “magnetic-field-assisted elastocaloric cooling” to enhance the temperature change up to 7.4 K, which is 20% higher than the sole elastocaloric effect. These results provide a basis for future studies of the multicaloric effect in metamagnetic shape memory alloys fabricated via AM.

Development and magnetocaloric properties of Ni(Co)-Mn-Sn printing ink

Magnetocaloric (MC) cooling is a vast research field nowadays which needs continuing development of MC materials. Besides, technological approaches of the fabrication and design of MC materials to be applied as the heat exchangers require a reinforcement. Heusler-type metamagnetic shape memory alloys (MetaMSMAs) exhibiting a large MC effect near room temperature, owing to the magnetic field induced first-order transformation, have been shown to be promising candidates for magnetic refrigeration, and the possibility of their fabrication by 3D printing technologies was experimentally demonstrated in the literature. In the present work we have elaborated a route for the room-temperature fabrication of MC ink incorporating the polymer binder and Ni(Co)-Mn-Sn MetaMSMA powder obtained from the preliminary melt-spun ribbon with tuned MC properties. The ink is used to print 2D films which do not require a subsequent heat treatment. The field-induced adiabatic temperature measurements reveal that the screen-printed samples displayed the same inverse MC effect as the ribbon, evidencing that room-temperature ink printing technology of MC intermetallics, elaborated for the first time in the present work, is promising for 2D printing of cooling microdevices for MEMS, flexible electronics etc. • A magnetocaloric powder based on metamagnetic shape memory alloys for additive manufacturing has been successfully obtained. • A magnetocaloric ink was developed using a sustainable approach, avoiding any hazardous product during its preparation. • Magnetocaloric materials printed by screen-printing technique show performance similar to that observed in the bulk ribbon.

Martensitic transformation near room temperature and hysteresis in (Ni–Co)50–Mn–Sn metamagnetic shape memory alloys

The martensitic transformation behaviors, magnetic properties, crystal structures, and entropy change (ΔS) of Ni50−xCoxMn50−ySny alloys were systematically investigated. Samples were prepared by induction melting, followed by solution heat treatment at 1273 K for 1 day and quenching. A magnetic phase diagram with a broad range of compositions was established, from which a series of alloys with varying Co concentrations was selected, such that their martensitic transformation starting temperatures (TMss) were near room temperature. The thermal and magnetic-field hystereses of these samples were systematically investigated, and a clear composition dependence was observed. The dissipation energy (Edis), which governs the transformation hysteresis, was found to be smaller for alloys with x = 5–8 than for those with x = 0–3. This behavior was found to originate from the difference in crystal structures of the martensite phases, i.e., the crystal structures of the martensite phases are 4O and 6M for x = 0–3 and x = 5–8, respectively. Moreover, the geometric compatibility between the parent and martensite phases was found to be the direct cause of the difference in dissipation energy in Ni–Co–Mn–Sn alloys.

Room temperature huge magnetocaloric properties in low hysteresis ordered Cu-doped Ni-Mn-In-Co alloys

The reduction of the thermal hysteresis in first order magnetostructural transition is a determining factor to decrease energy losses and to improve the efficiency of magnetocaloric cooling based systems. In this work, a Cu doped NiMnInCo metamagnetic shape memory alloy (MMSMA) exhibiting a narrow thermal hysteresis (around 5 K) at room temperature has been designed. In this alloy, the induced L21 ordering process affects the phase stability in an unusual way compared to that observed in NiMnInCo and other NiMn based alloys. This ordering produces an increase in the Curie temperature of the austenite but hardly affects the martensitic transformation temperatures. As a consequence, the ordering increases the magnetization of the austenite without changing the transformation temperatures, doubles the sensitivity of the transformation to magnetic fields (the Claussius-Clapeyron slope goes from 2.1 to 3.9 K/T), improves the magnetocaloric effect, the reversibility and finally, enhances the refrigeration capacity. In addition, the magnetic hysteresis losses are among the lowest reported in the literature and the effective cooling capacity coefficient RCeff reaches 86 J/Kg for 2 T (15 % higher than those found in Ni-Mn based alloys) and 314 J/Kg for 6 T fields. Therefore, the ordered alloy possesses an excellent combination of low thermal hysteresis and high RCeff, not achieved previously in metamagnetic shape memory alloys near room temperature.

Cd-doping effects in Ni–Mn–Sn: experiment and ab-initio study

Martensitic transformation (MT), magnetic properties, and magnetocaloric effect (MCE) in Heusler-type Ni47Mn40Sn13−x Cd x (x= 0, 0.75, 1, 1.25 at. %) metamagnetic shape memory alloys (MetaMSMAs) are investigated, both experimentally and theoretically, as a function of doping with Cd. Ab-initio computations reveal that the ferromagnetic (FM) configuration is energetically more favorable in the cubic phase than the antiferromagnetic (AFM) state in undoped and doped alloys as well. Moreover, it is revealed that the alloys in the ground state exhibit a tetragonal structure confirming the existence of MT, in agreement with the experiments. It was indicated, both in theory and practice, that a reduction of the unit cell volume and an increase of the MT temperature as a function of the Cd doping. Indirect estimations of MCE in the vicinity of MT were carried out by using thermomagnetization curves measured under different magnetic fields up to 5 T. The results demonstrated that the doped alloys exhibit enhanced values of the inverse MCE comparable with those of Ni-Mn-based MetaMSMAs. Maximum magnetic entropy change in a field change of 2 T increases from 3.0 for the undoped alloy to 3.4 and 5.0 for the alloys doped with 0.75 and 1 at.% of Cd, respectively. The inverse and conventional MCE were explored by direct measurements of the adiabatic temperature change under the magnetic field change of 1.96 T. The Cd doping increased the maximum of inverse MCE by nearly 78% from 0.9 K to 1.6 K for the undoped and doped alloys, respectively. The results depicted that Cd doping can effectively tailor the structural, magnetic, and MCE properties of the Ni–Mn–Sn MetaMSMAs.

Enhanced Magnetostrain in a A-Textured Ni44.5Co4.9Mn37.5In13.1 Alloy through Superelastic Training

Large magnetostrain can be demonstrated in Ni-Mn-X (X = In, Sn, Sb) meta-magnetic shape memory alloys by resuming the predeformed martensite through magnetic-field-induced reverse martensitic transformation. However, owing to the constraint from the self-accommodated microstructure and randomly distributed crystallographic orientation, spontaneous magnetostrain without predeformation in polycrystalline alloys remains low. Here, by combining microstructure texturing and superelastic training, enhanced spontaneous magnetostrain was achieved in a directionally solidified Ni44.5Co4.9Mn37.5In13.1 alloy with strong <0 0 1>A preferred orientation. After superelastic training through cyclic compressive loading/unloading on the directionally solidified alloy, a large spontaneous magnetostrain of ~0.65% was obtained by applying a magnetic field of 5 T, showing great improvement when compared to that of the untrained situation, i.e., ~0.45%. Such enhanced magnetoresponse is attributed to the internal stress generated through superelastic training, which affects the variant distribution and the resultant output strain in association with the martensitic transformation.

Demonstration of Principle of Low-temperature Thermal Power Generation Using Combination of Magnetic Phase Transformation Alloy and Magnetostrictive Vibrational Power Generator

Ni-Co-Mn-Sn metamagnetic shape memory alloys are known to show drastic change of magnetization upon martensitic transformation. For a selected composition, a steep magnetization change occurs slightly above room temperature. In this paper, we propose a structure which generates change of magnetic force by temperature difference between the room temperature and heat source using the alloy and two permanent magnets. By combining the structure and a magnetostrictive vibrational power generator consisting of Fe-Ga alloy plate, U-shaped frame, coil, and magnet, electrical energy can be taken out from a heat source of about 50°C. As this principle demonstration, the prototype using plate of Ni-Mn-Co-Sn alloy of 10×10×1.5 mm was confirmed that adsorption (heating of the alloy) and desorption (cooling) were repeated in about 200 seconds, and power generation by free vibration was carried out every time. It will be possible to extract energy necessary for radio communication from a low temperature heat source.

Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects

Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response to magnetic fields and uniaxial stress which can be utilized in single caloric or multicaloric cooling concepts for energy-efficient and sustainable refrigeration. However, during cyclic operation these alloys suffer from structural and functional fatigue as a result of their high intrinsic brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure design strategy which simultaneously improves cyclic stability and maintains the excellent magnetocaloric and elastocaloric properties. Our results reveal that precipitation of a strongly Fe-enriched and In-depleted coherent secondary γ-phase at grain boundaries can ensure excellent mechanical stability by hindering intergranular fracture during cyclic loading. In this way, a large elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without structural or functional degradation, which corresponds to an increase of the cyclic stability by more than three orders of magnitude as compared to single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the dual-phase material when the secondary γ-phase is exclusively formed at grain boundaries as the martensitic transformation within the Heusler matrix is barely affected. This way, an adiabatic temperature change of -3 K and an isothermal entropy change of 15 Jkg−1K−1 was obtained in 2 T for dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other single caloric and mutlicaloric materials, therewith paving the way for solid-state caloric cooling applications.

Observation of Atomic‐Order Engineered Martensitic Transformation in Ni45Co5Mn37In13 Metamagnetic Shape Memory Alloys

Engineering the martensite–austenite transformation interval (ΔT i) is important for optimizing the functionalities of metamagnetic shape memory alloys. Although it has been revealed that both doping and thermal annealing can influence ΔT i, the underlying mechanisms remain largely unexplored. Herein, a direct observation of the martensitic transformation process in Ni45Co5Mn37In13 alloys with distinct ΔT is is made. In contrast to the typical burst‐like martensitic transition, it is revealed that the alloy with a large ΔT i exhibits discretely distributed martensitic and austenite phases that evolve slowly with varying temperature. The unusual properties are found to be mainly correlated with atomic disorder rather than lattice distortions. The results indicate the great potential of atomistic engineering in manipulating the martensitic transformation for applications.

Analysis of the strain misfit between matrix and inclusions in a magnetically tunable composite

A magnetically tunable composite has been elaborated by embedding microparticles of a metamagnetic shape memory alloy on a photo curable resin. The strain misfit between the polymeric matrix and the inclusions has been analysed within Eshelby formalism. Results show the non-appearance of active microcracks at the interfaces where strains are induced by the martensitic transformation in the microparticles. Even though the martensitic transformation is well detected, the values of misfit β coefficient indicate that the matrix accommodates all the stresses induced by the inclusions. A stable surface interaction between particles and matrix is also confirmed during thermal cycles. It is also demonstrated that the damping capacity of the composites can be tuned by combining oscillating strain, fillers content and magnetic field. The proposed model could be applied to analyse the mechanical stability in polymer matrix composites in which fillers undergo a first order transition with volume change and associated deformation.

Martensitic transformation, magnetic entropy, and adiabatic temperature changes in bulk and ribbon Ni48Mn39.5Sn12.5\u2212xInx (x\u2009=\u20092, 4, 6) metamagnetic shape memory alloys

Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution.Graphic abstract