Heusler-type metamagnetic shape memory alloys (MMSMAs) exhibit a large functional response associated with a first-order martensitic transformation (MT). The strong magneto-structural coupling combined with the presence of mixed magnetic interactions enables controlling this MT by means of a magnetic field, resulting in different multifunctional properties, among them giant magnetoresistance, metamagnetic shape memory effect (MMSM), or inverse magnetocaloric effect (MCE). Not only the shift rate of MT as a function of the magnetic field but also its eventual suppression are key parameters in order to develop these effects. Here we present our findings concerning a detailed study of the magnetic field-induced MT and its suppression in MnNi(Fe)Sn MMSMAs, by applying strong steady magnetic fields up to 33 T. These measurements will lead to the creation of the T-μ0H phase diagrams of the MT. Moreover, we will also give light to the effect of Fe—content and, as a direct consequence, the magnetic coupling on the suppression of the magnetostructural transformation.

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.

This study explores the reversibility of the martensitic transformation (MT) and magnetocaloric (MC) response of the Ga-doped Ni50Mn35In15 magnetic shape memory alloys (MSMAs) with a Heusler structure. The direct and reverse MT occurs between temperatures TM ≈ 257K and TA ≈ 266K, respectively. The large MC effects resulting from the magnetic-field-induced first-order MT render these materials promising for room-temperature magnetic refrigeration. On account of both a low thermal hysteresis of MT (ΔThyst = 4K) at a magnetic field of 2T and a highly reproducible peak value of the adiabatic temperature change at MT (|∆Tad| ≈ 1.3K for µ0H = 1.9T), Ni50Mn34In15Ga1 MSMA emerges as a benchmark material for studying a cyclic stability of MC effects. During the first magnetic switching cycle, a reduction of ∆Tad at MT by approximately 1.3 is observed, significantly lower than the reported one for other MC materials undergoing similar first-order phase transitions. Subsequent cycles revealed a consistent stability of the magnetic-field-induced ∆Tad even after more than 200 magnetic field switching cycles. These findings suggest a notable degree of reversibility of the MT in the studied MSMA, which was also confirmed in the present work by a Temperature-First Order Reverse Curve distribution analysis.

Ni-Mn-Ga particles/polymer composites are new magnetostrain active materials suitable for actuation and sensing. In the present work, we prepared mechanically anisotropic samples of the "30 vol.% single crystalline Ni-Mn-Ga particles/silicone" composite material and systematically studied their cyclic stress-strain (S-S) evolutions along and perpendicular to the particle chains, while monitoring changes of magnetization curves. Four different compression cycling routes with the strain amplitude of 30% were explored. Magnetic measurements were served as the probes to indirectly detect microstructure changes of composite samples, whereas X-ray micro-CT images, alongside dimensions control of samples, were used for direct microstructural observations. The influences of the compression cycling routes on the parameters of S-S behaviors, such as an output stress, effective stiffness, and stress hysteresis, were revealed. It was found that the composite material after achieving equilibrium showed a rather good compression cycling stability of the mechanical and magnetic properties. It was revealed that composites being strongly deformed either along easy-magnetization axis (along the particle chains) or along hard-magnetization axis (perpendicularly to the particle chains) exhibited a magnetically harder behavior along the particle chains and magnetically easier behavior in the orthogonal direction, respectively. These unusual effects of a strong deformation of composite on its magnetization processes were discussed in terms of the particle rearrangements in the chains.

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) are promising materials for actuator and transducer devices. Their intrinsic brittleness and high fabrication cost in the bulk form are issues to be solved. One of the solutions is a development of composites comprising these materials as a filler component whereby representing an emerging research field in the FSMAs. To address the improvement and stability challenges of the magnetic field-induced martensitic variant reorientation (MVR) characteristics of the particles in the previously elaborated 'Ni-Mn-Ga single-crystalline particles/silicone rubber' composites and to unveil new aspects of their functional behaviors, in the present work, we have investigated MVR characteristics as a function of compression cycling and under huge in-situ opposing contractions. It was found that after cycling with the 30% of compressive strain along the particle chains, the value of switching magnetic field needed to start MVR events was notably reduced, whereas it was almost intact when in-situ measured under the same compression level. In-situ measurements of the 'magnetization versus magnetic field' curves of the composite squeezed by 50% or 70% did not show MVR blocking. Instead, they revealed both a drastic decrease of the MVR switching field and narrowing of the MVR interval caused by the barreling effect. The results can be useful for the development of novel types of actuators and transducers.

The magnetization value and electric resistivity of the single-crystalline sample of Ni50Fe19Co4Ga27 shape memory alloy were measured. The elastic modulus was determined by the Dynamic Mechanical Analysis (DMA). The characteristic temperatures of martensitic transformation (MT) of the alloy were estimated from the temperature dependences of magnetization, electric resistivity and elastic modulus. A significant disparity between MT temperatures resulting from DMA and those estimated from magnetic and resistivity measurements was discovered. It was argued that the discrepancy is caused by the non-uniform mechanical stressing of twinned single crystal by the DMA analyzer. Moreover, the DMA measurements revealed a significant decrease of the elastic modulus of twinned martensite under the applied magnetic field of 1.5 kOe. To explain this effect, the temperature-dependent Young’s modulus of twinned crystal lattice was computed. The computations showed that the experimentally observed field-induced change of the elastic modulus is caused by the stress-assisted detwinning of the crystal lattice by the applied magnetic field.

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

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.

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. %) meta-magnetic 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 meta-stable 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 anti-ferromagnetic 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 vertical bar 26.9GeJ/kgK at mu H-0 = 5 T and an adiabatic temperature change of vertical bar 1.5 vertical bar K at mu H-0 = 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.

A giant four-fold magnetic anisotropy (with an anisotropy field up to 4 kOe) was observed in the twinned NiMnGa epitaxial film. Its appearance is explained in terms of moderate coupling between twin variants having strong uniaxial magnetocrystalline anisotropies directed orthogonally when the intertwin exchange field is comparable with the anisotropy field. This finding paves the way to increase the order of magnetic anisotropy in a many-component system while keeping the value of the anisotropy field by tuning the intercomponent exchange strength and can be extended to exchange-coupled multilayers and arrays of nanoelements.

Polymer-based magnetoelectric (ME) composites, composed of magnetostrictive and piezoelectric phases, in addition to exhibiting an effective coupling between the magnetic and electric orders of the matter, also offer important advantages for the Internet-of-Things, digitalization, and 4.0 revolution environments: light weight, flexibility, wearability, environmental friendliness, printability, and biocompatibility. Nevertheless, their successful implementation on applications such as sensors, actuators, energy harvesters, biomedical devices and spintronics strongly depends on the increase of its ME voltage response. This work explores, both experimentally and theoretically, the magnetostrictive Ni-Mn-Ga's martensite - austenite phase transformation to shift/tailor/design the ME resonance peak exhibited by Ni-Mn-Ga/P(VDFTrFE) piezoelectric composites. In the austenite phase, the determined peak value of the ME coefficient of 18.1 V cm-1 Oe-1 was much higher than the value of 6.05 V cm-1 Oe-1 obtained for the martensite phase, whereas the estimated theoretically value of magnetoelastic constant in the austenite is much smaller. The ways to further increase the magnetically induced ME response are also outlined.

Iron-based alloys with compositions close to Fe75Al25 (at.%) attract much attention due to their unique properties useful, e.g., for high-temperature or high damping engineering applications. Their mechanical, electron transport and magnetic properties strongly depend on the structural characteristics. In this paper we carried out a comparative study of the physical properties of the as spun ribbons Fe70Al30 and Fe70Al20Cr10 (at.%) alloys. The ribbons were produced using the melt spinning technique and were characterized by SEM, X-ray diffraction, differential scanning calorimetric, resistivity measurement and vibrating sample magnetometer. The addition of Cr to Fe70Al30 has a significant influence on atomic ordering, increases the electrical resistivity and a strong influence on the magnetic behavior.

We anticipate and demonstrate experimentally the mechanical-to-electrical energy conversion through the variation of magnetization resulting from a periodical stress-induced martensitic transformation in the single crystalline Co-Ni-Ga ferromagnetic shape memory alloy. Dynamic loading in a stress-induced austenite-martensite two-phase state was performed with the peak-to-peak strain amplitude from 0.002 to 0.024 in a frequency range of 25 - 150 Hz. A reproducible superelastic behavior occurred at all frequencies. Alongside this remarkable result, we found that the electrical power output depends quadratically on the peak-to-peak strain. This study suggests a new route for the development of broad-band vibration energy harvesting devices.

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.

The influence of the W-doping on the martensitic transformation, magnetic properties and exchange bias (EB) effect in the Ni47Mn40Sn13-xWx(x= 0, 0.5, 1, 1.25 at.%) magnetic shape memory alloys has been investigated. It is found that the W-doping causes a simultaneous reduction of both the ferromagnetic (FM) exchange coupling and enhancement of the magnetic anisotropy, leading to a decrease of the magnetic moment of the low-temperature phase and to a higher attainable EB. The magnetic memory measurements reveal the presence of a glassy magnetic ground state, which can significantly impact the reduction of magnetization and enhancement of EB in the studied bulk alloys. It is argued that the glassy magnetic ground state originates from the partial magnetic disorder resulting from the correlation between the antiferromagnetic and FM states. The results demonstrate that the doping by W instead of Sn is an efficient tool to tailor the EB effect in the Ni-Mn-Sn-based Heusler alloys, whereby they are promising for spintronic applications.

A B S T R A C TSolid-state refrigeration is a promising alternative to the less-efficient conventional gas compressionexpansion cooling, magnetocaloric (MC) cooling being the most elaborated method nowadays for solid-state refrigeration. The development of intermetallic compounds exhibiting first-order magnetostructural transformations as a source of giant MC effect is at the core of this research field. For high-efficient heat exchanger in refrigeration applications, the MC material should show a large surface area for heat transfer and geometric freedom for a low pressure drop of the liquid coolant. To satisfy these conditions the machining of MC materials is hardly possible, due to the inherent brittleness of intermetallics. In this context, additive manufacturing (AM) arises as the most suitable option to ensure the geometric freedom for adapting designs of solid state cooling devices. Elaboration of AM methods for the fabrication of MC materials such as the Heusler type NiMnSnbased metamagnetic shape memory alloys (MetaMSMAs) is a complex challenge related to the efficient transfer of the functional characteristics of the master alloy into its powder form and then in the AM product. In the present work this problem was solved by introducing an intermediate production of melt-spun ribbons with tuned transformation, magnetic and MC characteristics. The ribbons served for the preparation of the MC powder which readily exhibited previously tuned characteristics. The MC powder and the selected polymer binder were used to prepare a room temperature printable ink. It was found that the screen-printed samples displayed the same inverse MC effect as the ribbon, evidencing that printing technology of MC intermetallics, elaborated for the first time in the present work, is promising for 2D printing of cooling microdevices for flexible electronics as well as for 3D printed MC coolers.

Heusler-type Ni-Mn-based ferromagnetic and metamagnetic shape memory alloys (FSMAs and MetaMSMAs) are the special multifunctional materials, particularly, suitable for the magnetic actuation owing their strong magnetoelastic coupling: anisotropic in FSMAs and isotropic in MetaMSMAs. The magnetostrictive properties of these two groups of materials are overviewed in the present article. It is shown experimentally and theoretically that the anisotropic magnetostriction plays the key role in the occurrence of the giant magnetostrain effect in the martensitic state of FSMAs, whereas MetaMSMAs exhibit a large magnetostrain due to the magnetic field induced martensitic transformation accompanied by a noticeable volume change.

In this work, CoFe(2)O(4 )magnetic nanoparticles (MNPs) were synthesized by an eco-friendly co-precipitation method. The effect of Triethylene glycol (TEG) coating on the structural, magnetic and magnetothermal prop-erties of MNPs was investigated. The formation of crystalline MNPs with a cubic spinel structure and the single phase state was confirmed by the X-ray diffraction (XRD) and infrared spectra (FT-IR) techniques. The spherical morphology and aggregation of the MNPs, as a sign of the presence of interparticle interactions, were revealed by the field emission scanning electron microscopy imaging. A remarkable result has been found by the SQUID and Mo spacing diaeresis ssbauer spectroscopy measurements revealing that the polymer coating increases the saturation magnetiza-tion through the control of the metal-oxygen-metal bonds and reduction of the spin disorder at the nanoparticle surface. Furthermore, the Henkel plots indicated a dominant role of the dipole-dipole over exchange magnetic interactions in the samples which affected the heating efficiency of the ferrofluids measured under different AC magnetic fields (2.2, 2.7, and 3.3 mT) with a frequency of 92 kHz showing a linear dependence of the thermal efficiency with the AC field amplitude. It was shown that TEG coating increases the heating efficiency of the CoFe(2)O(4 )MNPs, which was attributed to an increase in saturation magnetization and a decrease in the strength of the magnetic interactions between the coated nanoparticles.

In view of the exponential rate of advancement in robotics technology, a composite material, which is promising for high-speed and large-strain actuation and sensing applications, has been developed in this study. Single-crystalline Ni49.9Mn28.5Ga21.6 (SC Ni-Mn-Ga) ferromagnetic shape memory alloy particles were fabricated from the polycrystalline Ni-Mn-Ga alloy by a well-controlled mechanical crushing. X-ray diffractions revealed a mixture of 5M- and 7M-martensitic phases in the SC Ni-Mn-Ga particles. A composite consisting of the silicone rubber and 20 vol.% of the crystallographically and spatially oriented SC Ni-Mn-Ga particles was fabricated by curing under a magnetic field and the chain-oriented structure was confirmed by a micro-computed tomography. This composite, which exhibited a magnetic field induced rubber-like behavior with a magnetostrain as high as 4.0% despite reduced filling factor, was attributed to the co-existence of the 5M- and 7M-martensitic phases.

A series of samarium doped cobalt ferrites with the nominal compositions of CoSmxFe2-xO4 (where x = 0, 0.02, 0.04, and 0.06 at.%) was synthesized using sol-gel auto-combustion method. The crystal structure, morphology and magnetic properties of the nanoparticles have been investigated. The XRD data analyzed by the MAUD program confirmed the successful substitution of Fe3+ by Sm3+ cations in the unit cell of the cobalt ferrite lattice. The formation of nanosized spinel ferrites was confirmed by FESEM and FTIR analysis. The values of saturation magnetization (M-S) decreased from 76 emu/g to 63 emu/g by increasing the Sm content from x = 0 to x = 0.06 at room temperature, whereas at 10 K, the decreasing tendency of MS was much weaker. The reduction of temperature from 300 to 10 K caused a remarkable growth of both the saturation magnetization and coercive field (H-C). The coercivity of the sample with x = 0.06 at 10 K is strongly higher than the one at the room temperature. The influence of samarium ions and temperature-dependent magnetic response of CoFe2O4 nanoparticles was studied and their effect was discussed in terms of the geometrical proportions and magnetic anisotropy evolutions. The Sm doped cobalt ferrite is a suitable candidate for moderate permanent magnets and high density information storage, especially when in use at low temperatures.