Rapidly solidified Fe-Pd-Ga ferromagnetic shape memory ribbons, containing 1 and 3 at. % Ga, were obtained, and annealed at 950 degrees C for 15 and 30 min. Gallium substitution destabilizes the cubic lattice but preserves ferromagnetic order; thereby, it modifies phase stability and magnetic sensitivity. The combined effects of composition and heat treatment on microstructure, martensitic transformation temperatures, transformation heat, kinetics, and magnetic-field-induced transformation shift are presented. Magnetic sensitivity is evaluated using thermomagnetic and magneto-elastic measurements, being further validated through Clausius-Clapeyron analysis. Short-time heat treatment enhances structural relaxation and significantly increases the transformation heat, whereas prolonged annealing promotes grain growth and precipitate formation without suppressing thermoelastic behavior. Increasing Ga content results in a pronounced linear increase of the martensitic transformation temperature with magnetic field, from approximately 0.6 K T-1 for 1 at. % Ga to about 1.45 K T-1 for 3 at. % Ga. The good agreement between thermomagnetic measurements and Clausius-Clapeyron analysis confirms that the transformation shift is primarily governed by intrinsic thermodynamic parameters. The smaller magneto-elastic response indicates that microstructure limits strain expression. Therefore, functional control requires tuning the balance between intrinsic thermodynamic driving forces and microstructure-dependent magneto-elastic effects through composition and heat treatment. This enables the design of thermally adaptive and magnetically programmable materials, where 3 at. % Ga composition is suitable for active magnetic control and that of 1 at. % Ga is optimized for enhanced thermal stability and precision sensing.

Melt-spun Fe70−xPd30Gax ribbons (x = 1 and 3 at.% Ga) were heat-treated at 1223 K for 1 h and 2 h and characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, magnetometry, and magnetoelastic measurements. Increasing Ga content decreases thermodynamic equilibrium temperature from 292.0 K (1 at.% Ga) to 283.5 K (3 at.% Ga) in as-prepared ribbons. Extended heat treatment then shifts it to 288.0 K and 264.5 K, respectively, and promotes Fe-rich precipitation. Fine precipitates at 1 h preserve a large transformable matrix fraction and introduce microstructural heterogeneity that governs variant mobility and domain-wall pinning; prolonged annealing triggers coalescence, depleting the matrix and reducing both the transformation heat and the magnetoelastic response. Kissinger analysis yields apparent activation energies of 338 kJmol−1 (1 at.% Ga) and 228 kJmol−1 (3 at.% Ga), confirming that higher Ga content lowers the transformation energy barrier. The magnetostrictive response depends on annealing: 1 h-annealed samples exhibit field-induced variant reorientation and saturation magnetostriction of ~60 ppm at 200 K, whereas 2 h-annealed samples approach volume-conserving behavior. Coercivity scales with precipitate density, with Ga3-2h showing anomalously soft magnetic behavior following coalescence. Thermally induced precipitation thus emerges as a route to simultaneously control microstructure, transformation kinetics, magnetoelastic response, and magnetic behavior in ferromagnetic shape memory alloys.

Rapidly solidified Fe-Pd-based ferromagnetic shape memory alloy ribbons, modified with Mn or Ga additions, were produced and subjected to post-solidification heat treatments of varying duration to investigate the interplay between composition, surface characteristics, and functional properties. Surface morphology and wettability were evaluated alongside corrosion behavior, magnetic response, martensitic transformation, and in vitro cell adhesion. Corrosion performance was assessed through immersion and electrochemical techniques, providing insight into degradation kinetics. The results reveal a complex coupling between surface properties, corrosion resistance, and cell adhesion responses. Binary Fe-Pd ribbons exhibit moderately rough, homogeneous surfaces with stable Wenzel-type wetting, but limited electrochemical stability due to the reactivity of iron. Mncontaining ribbons display heterogeneous surface features and locally poor wettability after short heat treatments, leading to reduced corrosion resistance and degradation of magnetic and martensitic properties; nevertheless, they support favorable fibroblast adhesion. Prolonged annealing improves surface uniformity and wettability, while maintaining moderate corrosion resistance and good cell adhesion. Ga-containing ribbons show highly nonuniform topography combined with good hydrophilicity and the highest corrosion resistance, attributed to the formation of stable Ga-O protective products. Although corrosion effects are mitigated, partial suppression of magnetic and martensitic responses is observed. The findings highlight the potential of Fe-Pdbased ferromagnetic shape memory alloy ribbons as degradable biomedical substrates.

Magnetic ceramic nanostructures of the type xDy2O3-(1-x)alpha-Fe2O3 (x=0.1 and 0.5) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The 0-h Mӧssbauer spectrum was analyzed with a sextet characteristic to hematite. A second sextet for x=0.5 and a second and third sextet for x=0.1, with lower values of the hyperfine magnetic field, were assigned to dysprosium-doped hematite. An additional quadrupole-split doublet, whose relative abundance increased with the ball milling time and molar concentration, was assigned to superparamagnetic dysprosium iron perovskite (dysprosium orthoferrite) phase. The X-ray diffraction (XRD) patterns for the molar concentration x=0.5 showed the presence of DyFeO3 peaks after 12 h of milling. The hysteresis loops recorded at 5 K and an applied magnetic field of 5 T exhibited coercive fields that increased with ball milling time, while the hysteresis loops at 300 K were consistent with a strong paramagnetic component. The zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe and 5-300 K showed the effect of milling time on the Morin transition of hematite. The optical diffuse reflectance spectra showed that the samples were semiconductors with a band gap of ~2.1 eV.

The Ni49+xMn32-2xGa19+x (x = 0; 2) Heusler ferromagnetic shape memory alloys were prepared using spark plasma sintering using raw flake-type powders obtained by soft grinding melt-spun ribbons. Samples were characterized using x-ray diffraction, electron microscopy, thermal analysis, and bending tests. Although the properties of ribbons and corresponding powders show similar properties' tendencies, they are opposite in the bulk sintered alloys when compared with precursor powders. Namely, Ni49Mn32Ga19 bulk shows a higher enthalpy (5.8 J g-1), an increased martensitic transformation (MT) temperature (by 9 K), and a reduced hysteresis span (5 K). Conversely, for the Ni51Mn28Ga21 sintered sample, a lower enthalpy (2 J g-1), a significant decrease (by 40 K) in the MT starting temperature, and a broadening of the hysteresis range (26 K) were observed. This difference is analyzed versus specific features of the microstructure. Moreover, the activation energy and the pre-exponential factor of the MT, extracted through kinetic analysis within two non-isothermal models, Kissinger and Friedman, complement and sustain these findings. Fractography details of the sintered samples are discussed in relation to the stress-strain curves from the bending tests. The Ni49Mn32Ga19 bulk sample exhibits a higher bending strength (260 MPa) and a lower strain (0.55%) than the Ni51Mn28Ga21 sample (177 MPa and 0.61%). The observed dependence of functional characteristics on preparation enables the possibility of property control required for various applications and suggests that the proposed route is promising in this regard for further investigations.

The xGa2O3*(1-x)Fe2O3 (x=0.5) was prepared by mechanochemical activation using high energy ball milling for times of 0, 2, 4, 8, and 12 hours. The magnetic properties were studied by hysteresis loop measurements with an applied magnetic field of 5 T at temperatures of 5 and 300 K. Zero-field-cooling-field-cooling results were obtained in a magnetic field of 200 Oe in the temperature range 5-300 K. The magnetization and average coercive field were investigated as functions of ball milling time and temperature. They were related to changes in the average grain size, induced stresses and defects, variations in exchange coupling and magnetic ordering. ZFC did not exhibit a sharp edge, so we do not witness superparamagnetism with a well-defined blocking temperature. The Morin transition of hematite occurred over broad temperature ranges and was monitored as a function of ball milling time. The Dzyaloshinskii-Moriya antisymmetric exchange interaction explained the gradual increase in the magnetization with ball milling time.

When a severe plastic deformation (SPD) process is performed at high temperatures, it becomes more versatile. Designed originally for the bulk nanoconstruction of hard-to-deform alloys, high-speed high-pressure torsion (HSHPT) is an SPD method used in this research for assembling multiple layers of shape memory nanocomposites. Three hard-to-deform magnetic alloys in the cast state were used. Soft magnetic shape memory alloys, NiFeGa and FePdMn, and a potentially hard magnetic alloy, CoZr, were assembled in various composites. Both grain refinement and strong layer bonding were achieved in ZrCo/FePdMn and ZrCo/NiFeGa composites in seconds. The very short SPD time is specific to HSHPT because of the intense friction that occurs under high pressures, which generates huge amounts of heat. After SPD, the temperature rises in bulk material like a pulse, being dissipated mostly through heat conduction. The SPD parameters were carefully controlled with an advanced automation system using a programmable logic controller. Nevertheless, the major drawbacks of high-pressure torsion were overcome, and large SPD discs were obtained. Various investigation techniques (optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy) show well-defined interfaces as well as a fine and ultrafine structure.

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mossbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mossbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mossbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mossbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5-300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV-Vis-NIR region of the spectrum was found to increase with BMT.

Mixed-oxide nanostructures of the type xSm2O3-(1-x)alpha-Fe2O3 (x=0.1 and 0.5) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The 0-h Mӧssbauer spectrum was analyzed with a sextet characteristic to hematite. A second sextet with a lower value of the hyperfine magnetic field was assigned to samarium-doped hematite. An additional quadrupole-split doublet, whose abundance showed a general trend to increase with the ball milling time, was attributed to superparamagnetic samarium iron perovskite (samarium orthoferrite) phase. The X-ray diffraction (XRD) patterns for the equimolar composition were dominated by the diffraction peaks of SmFeO3 after 12 h of milling. The hysteresis loops recorded at 5 K and an applied magnetic field of 5 T exhibited higher values of the magnetization than the similar ones measured at 300 K, but did not saturate at this field strength. The coercive field values showed a decrease with decreasing the particle size after prolonged milling. The zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe and 5-300 K were consistent with an increase in magnetization with ball milling time. The Tauc plots derived from the optical diffuse reflectance spectra showed that the samples were semiconductors with a band gap of ~2.1 eV.

In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.

Shape memory alloys, especially ferromagnetic shape memory alloys, are interesting new materials for the manufacturing of stents. Iron–palladium alloys in particular can be used to manufacture self-expanding temporary stents due to their optimum rate of degradation, which is between that of magnesium and pure iron, two metals commonly used in temporary stent research. In order to avoid blood clotting upon the introduction of the stent, they are often coated with anticoagulants. In this study, sulfated pectin, a heparin mimetic, was synthesized in different ways and used as coating on multiple iron–palladium alloys. The static and dynamic prothrombin time (PT) and activated partial thromboplastin time (APTT) of the prepared materials were compared to samples uncoated or coated with polyethylene glycol. While no large differences were observed in the prothrombin time measurements, the activated partial thromboplastin time increased significantly with all alloys coated with sulfated pectin. Aside from that, sulfated pectin synthesized by different methods also caused slight changes in the activated partial thromboplastin time. These findings show that iron–palladium alloys can be coated with anticoagulants to improve their utility as material for temporary stents. Sulfated pectin was characterized by nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy, and the coated alloys by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).

We present a simple two-dimensional model for a phase transition, then study its predictions, in particular the memory properties. The direct transformation is modeled by randomly placing small squares, "nuclei", on an initially empty surface. Then, the nuclei expand ("grow") up to finite final sizes which are randomly chosen in a given range, while keeping their square shape. An important issue is the "interaction" which forces some squares to remain at smaller sizes if the surrounding squares get in the way of their growth. Interestingly, this naturally leads to quasiequal total area covered by the squares of each size after a complete direct transformation. Next, it is shown that the system "remembers" incomplete ("arrested") reverse transformations taking place in reversed order of the squares sizes. The memory is "encrypted" in the distribution of the squares sizes after a next direct transformation and manifests as a significant imbalance between the areas covered by the "big" and "small" (relative to the arrest size) squares. We are able to also reproduce the so-called "hammer effect" and the memorizing of multiple arrest points. Our model is particularly relevant for the thermal memory effect in shape memory alloys, and we actually borrowed many features from existing thermodynamic models addressing this effect. However, here we eliminate the explicit thermodynamics and end up with a statistical geometry model, presumably easier to reproduce.

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

Yttrium iron garnet nanoparticles were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h, with and without graphene nanoparticles. The samples were subsequently characterized by Mo center dot ssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflec-tance spectroscopy. Examination of the quadrupole doublet's abundance as function of ball milling time indi-cated that graphene slowed down the precipitation of the yttrium iron perovskite (yttrium orthoferrite) phase. The increased linewidth of the doublet showed that the carbon from graphene preferentially entered the lattice of the yttrium orthoferrite. The saturation magnetization decreased with decreasing particle size for prolonged milling due to the occurrence of the antiferromagnetic hematite phase. The enhanced absorption in the infrared region could be associated with the incorporation of carbon from graphene in the lattice of the yttrium ortho-ferrite. The results are interesting for sensing and microwave applications.

The influence of processing on the martensitic transformation and related magnetic properties of the Ni55Fe18Nd2Ga25 ferromagnetic shape memory alloy, as bulk and ribbons prepared by the melt spinning method and subjected to different thermal treatments, is investigated. Structural, calorimetric, and magnetic characterizations are performed. Thermal treatment at 1173 K induces a decrease in both the Curie and the martensitic transformation temperatures, while a treatment at 673 K produces the structural ordering of the ribbons, hence an increase in TC. A maximum value of the magnetic entropy variation of −5.41 J/kgK was recorded at 310 K for the as quenched ribbons. The evaluation of the magnetoresistive effect shows a remarkable value of −13.5% at 275 K on the bulk sample, which is much higher than in the ribbons.

Magnetic ceramic nanoparticles system xNd(2)O(3)-(1-x)alpha-Fe2O3 (x = 0.1, 0.3 and 0.5) was synthesized by mechanochemical activation starting from hematite and neodymium oxide precursors and characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. Rietveld refinement of XRD data evidenced the formation of neodymium orthoferrite NdFeO3 as an end-product with a particle size of about 22 nm, determined using the Scherrer method for x = 0.5. The Mossbauer spectra were typically analyzed considering 2 sextets, corresponding to hematite and neodymium orthoferrite and a doublet, representing superparamagnetic particles (SPM). The recoilless fractions were determined using our dual absorber method and were found consistent with a decrease in particle size as consequence of the ball milling process performed.

Durable biocompatible metal vascular implants are still one of the significant challenges of contemporary medicine. This work presents the preparation of ferromagnetic biomaterials with shape memory in metal strips based on FePd (30 at% Pd) that is either not doped or doped with Ga and Mn, coated with poly(benzofuran-co-arylacetic acid) or polyglutamic acid. The coating of the metal strips with polymers was achieved after the metal surface had been previously treated with open-air cold plasma. The final functionalization was performed to induce anti-thrombogenic/thrombolytic properties in the resulting materials. SEM-EDX microscopy and X-ray photoelectron microscopy (XPS) determined the morphology and composition of the metal strips covered with polymers. In vitro tests of standardized thromboplastin time (PTT) and prothrombin time (PT) were performed to evaluate the thrombogenicity of these biofunctionalized materials for future possible monitoring of the implant in patients.

The paper presents the research results in the field of TiNiCu shape memory alloys processed by powder metallurgy techniques. The powders mixtures used to synthesize Ti50Ni30Cu20 alloys were obtained by blended constitutive elemental powders or by mechanical alloying of powder mixtures for 10 and 20 hours, respectively. Finally, a subsequent annealing process was carried out, followed by a rapid cooling in ice water. All experiments were performed under 99.9% argon atmosphere. At room temperature, the obtained materials contained monoclinic and orthorhombic martensite type. The structural and thermal investigation of these materials were discussed in view of the potential development of actuators.

The influence of the rapid solidification technique and heat treatment on the martensitic transformation, magnetic properties, thermo- and magnetic induced strain and electrical resistivity is investigated for the Cu doped NiMnGa Heusler-based ferromagnetic shape memory ribbons. The martensitic transformation temperatures are unexpectedly low (below 90 K-which can be attributed to the disordered texture as well as to the uncertainty in the elements substituted by the Cu), preceded by a premartensitic transformation (starting at around 190 K). A thermal treatment slightly increases the transformation as well as the Curie temperatures. Additionally, the thermal treatment promotes a higher magnetization value of the austenite phase and a lower one in the martensite. The shift of the martensitic transformation temperatures induced by the applied magnetic field, quantified from thermo-magnetic and thermo-magnetic induced strain measurements, is measured to have a positive value of about 1 K/T, and is then used to calculate the transformation entropy of the ribbons. The magnetostriction measurements suggest a rotational mechanism in low fields for the thermal treated samples and a saturation tendency at higher magnetic fields, except for the temperatures close to the phase transition temperatures (saturation is not reached at 5 T), where a linear volume magnetostriction cannot be ruled out. Resistivity and magnetoresistance properties have also been measured for all the samples.

The influence of the partial substitution of Fe by Si and thermal treatments on the structural, magnetic and magnetostrictive properties of the Fe67.5Pd30.5Si2 rapidly solidified ribbons has been investigated. A remarkable decrease in the martensite transformation temperature, with ~ 65 K lower than that of the Fe–Pd archetype alloy, is observed in the as-prepared ribbons. The thermal treatments shift the martensite transformation temperatures upward, with approximately 13 K for the higher thermal treatment. Also, these induce an improvement in the crystallinity in these ribbons with high texture and an increase in the crystallite size as a result of reducing the internal defects and stress. The thermodynamic considerations discussed in the frame of the Clapeyron–Clausius relation by using the calorimetric and thermomagnetic measurements (up to 7 T) reveal a weak influence of the magnetic fields on the martensitic transformation temperatures (~ 0.5 K/T). The magnetostriction decrease with temperature under small magnetic fields was discussed, beside an unusual behaviour in the technically saturated domain. This behaviour is based on the coexistence of the ordinary and forced magnetostrictions, the last one increasing faster with the temperature decreasing.