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Large recoverable strain of more than several percent arising from superelasticity in shape memory alloys is important for actuators, sensors, and solid-state refrigeration. Here, we report a Ni50.0Mn31.4Sn9.6Fe9.0 magnetic microwire showing a giant tensile recoverable strain of about 20.0% along the ⟨001⟩ direction of austenite at 263 K. The recoverable strain represents the largest value reported heretofore in Ni-Mn-based shape memory alloys and is also larger than that of the Ni-Ti wire available for practical applications at present. This giant tensile superelasticity is associated with the stress-induced two-step transformation, and the transformation sequence could be L21 (austenite) → 6M (six-layered modulated martensite) → NM (non-modulated martensite), as suggested by the temperature-dependent in-situ synchrotron high-energy X-ray diffraction experiments and the transformation strain calculation based on the crystallographic theory of martensitic transformation. In addition, this Ni50.0Mn31.4Sn9.6Fe9.0 microwire shows a transformation entropy change ΔStr of 22.9 J kg−1 K−1 and has the advantages of easy fabrication and low cost, promising for miniature sensor, actuator, and solid-state refrigeration applications. [ABSTRACT FROM AUTHOR]

Fe-Mn-Ga magnetic shape memory alloys can undergo martensitic transformation (MT) from a paramagnetic cubic phase to a ferromagnetic tetragonal phase. The MT is accompanied by a large volume change; yet, these alloys have never been explored for technological applications as negative thermal expansion (NTE) materials. Here, by careful chemical modification, tunable NTE characteristics including wide operating temperature windows (ΔT) and large negative linear coefficients of thermal expansion (αl) have been achieved in Fe44−xMn28Ga28+x (x = 1, 2, and 2.5) alloys. Typically, a giant NTE ΔT of 81 K and αl = −50.2 × 10−6 K−1 were realized in the Fe43Mn28Ga29 alloy upon cooling from 290 K. The relationships between the NTE features, the MT, and the substitution of Ga for Fe were discussed. Furthermore, the Fe-Mn-Ga alloys possess excellent mechanical properties, high electrical conductivity and high thermal conductivity. With these advantages, the Fe-Mn-Ga magnetic shape memory alloys show promising prospects for use as advanced NTE materials. [ABSTRACT FROM AUTHOR]

High-performance magnetocaloric materials should have a large reversible magnetocaloric effect and good heat exchange capability. Here, we developed a Ni48.1Co2.9Mn35.0In14.0 metamagnetic shape memory microwire with a large and reversible inverse magnetocaloric effect. As compared to the bulk counterpart, the microwire shows a better combination of magnetostructural transformation parameters (magnetization difference across transformation ΔM, transformation entropy change ΔStr, thermal hysteresis ΔThys, and transformation interval ΔTint) and thus greatly reduced critical field required for complete and reversible magnetic-field-induced transformation. A strong and reversible metamagnetic transition occurred in the microwire, which facilitates the achievement of large reversible magnetoresponsive effects. Consequently, a large and reversible magnetic-field-induced entropy change ΔSm of 12.8 J kg-11K-1 under 5 T was achieved in the microwire, which is the highest value reported heretofore in Ni-Mn-based magnetic shape memory wires. Furthermore, since microwires have a high surface/volume ratio, they exhibit very good heat exchange capability. The present Ni48.1Co2.9Mn35.0In14.0 microwire shows great potential for magnetic refrigeration. This study may stimulate further development of high-performance magnetocaloric wires for high-efficiency and environmentally friendly solid-state cooling. [ABSTRACT FROM AUTHOR]

Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (~8K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications. [ABSTRACT FROM AUTHOR]

Understanding the role of fine coherent precipitates in the micromechanical behavior of precipitate-strengthened shape memory alloys (SMAs), which still remains a mystery heretofore, is of crucial importance to the design of advanced SMAs with optimal functional and mechanical properties. Here, we investigate the lattice strain evolution of, and the stress partition between the nanoscale Ni4Ti3 precipitates and the matrix in a precipitate-strengthened Ni-Ti SMA during different deformation stages by in-situ synchrotron high-energy X-ray diffraction technique. We found that, during R-phase reorientation and stress-induced martensitic transformation, which both involve the shear deformation process, the lattice strain of the nanoscale precipitates drastically increases by a magnitude of 0.5%, which corresponds to an abrupt increase of ~520 MPa in internal stress. This indicates that stress repartition occurs and most of the stress is transferred to the precipitates during the shear deformation of the matrix. It is further revealed that the nanoscale precipitates which only have a low volume fraction bear a considerable amount of applied stress during all deformation stages investigated, implying that the nanoscale precipitates play an important role in the deformation behavior of the precipitate-strengthened Ni-Ti SMAs. [ABSTRACT FROM AUTHOR]

Superelastic behavior is traditionally related to the martensitic transition with a collective transformation scenario in some shape memory alloys. A kind of quasi-linear superelasticity accompanied by a finite avalanche or confined martensitic transformation was recently found in some alloy systems with strain glass state. Here, an in situ neutron diffraction technique was used to study the deformation behavior in an Ni43Fe18Ga27Co12 alloy with strain glass state in order to reveal the new intrinsic physical nature of the quasi-linear superelasticity. A significant modulus softening prior to the stress-induced martensitic transformation was observed during compression in the studied alloy, which is similar to the characteristics exhibited in the tweed precursor phenomena prior to temperature-induced martensitic transformation. Moreover, the diffraction peak broadening was further shown during the elastic stage of deformation for both single-crystal and polycrystalline samples, which mainly stems from the short-range fluctuation in the strain field inside each grain based on Williamson-Hall analysis. The authors believe that there exists a spatial heterogeneity in the modulus of the confined martensitic transformation alloy. [ABSTRACT FROM AUTHOR]

NiMn-based Heusler-type multiferroic alloys have attracted intensive attention due to their fascinating multifunctional properties such as magnetic shape memory, magnetocaloric effect, and magnetoresistance. The recently elucidated superparamagnetism and superspin glass behaviors in these alloys could greatly impact their multifunctional properties. This article provides an overview on the recent research progress on superparamagnetism and superspin glass behaviors in NiMnbased multifunctional alloys. The corroboration of these magnetic behaviors in the low-temperature phase is demonstrated and the possible origin of the magnetic clusters responsible for these magnetic behaviors is discussed. The open scientific issues in this research area are highlighted. [ABSTRACT FROM AUTHOR]

We report a giant effective magnetic refrigeration capacity in a Ni40Co10Mn40Sn10 multifunctional alloy. With a large magnetization difference between austenite and martensite, this alloy shows a strong magnetic field dependence of transformation temperatures. Complete magnetic-fieldinduced structural transformation and a considerable magnetic entropy change are observed in a broad operating temperature window of 33K near room temperature. Consequently, an effective magnetic refrigeration capacity of 251 J/kg for 5 T is achieved, which is the largest value for Ni-Mn-based Heusler alloys and comparable to that of the high-performance Gd-Si-Ge and La-Fe-Si magnetocaloric materials. Incorporating the advantages of low cost and non-toxicity, this alloy shows very promising prospects for room-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) have received great attention during the past decade due to their giant magnetic shape memory effect and fast dynamic response. The crystal structure and crystallographic features of two Ni-Mn-Ga alloys were precisely determined in this study. Neutron diffraction measurements show that Ni48Mn30Ga22 has a Heusler austenitic structure at room temperature; its crystal structure changes into a seven-layered martensitic structure when cooled to 243K. Ni53Mn25Ga22 has an I4/mmm martensitic structure at room temperature. Electron backscattered diffraction (EBSD) analyses reveal that there are only two martensitic variants with a misorientation of ~82° around <110> axis in each initial austenite grain in Ni53Mn25Ga22. The investigation on crystal structure and crystallographic features will shed light on the development of high-performance FSMAs with optimal properties. [ABSTRACT FROM AUTHOR]

A recent study by high-resolution neutron powder diffraction provided accurate crystallographic information for the newly developed ferromagnetic shape memory alloy 53 at.%Ni–25 at.%Mn–22 at.%Ga. This made it possible to study by high-resolution electron backscatter diffraction the local microstructures and the twinning relationships between martensitic variants. The twin interfaces were also investigated and they are found to be coherent on the {112} planes. [ABSTRACT FROM AUTHOR]

A ferromagnetic shape memory alloy of Ni48Mn30Ga22 prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni48Mn30Ga22 has a cubic L21 Heusler structure at room temperature, the same as that in the stoichiometric Ni2MnGa. When cooled to 243 K, the Ni48Mn30Ga22 alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni–Mn–Ga alloys with higher martensitic transformation temperatures. [ABSTRACT FROM AUTHOR]

The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ∼8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ∼0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training. [ABSTRACT FROM AUTHOR]

The composition dependent phase transformation and magnetic properties of the Ni50-xCoxMn39Sn11 (0≤x≤10) alloys were systematically investigated. Based on the obtained results, the phase diagram of this alloy system was established. Considering the combination of large magnetization difference across phase transformation ΔM and small transformation entropy change ΔS, the optimal composition range of 5≤x≤8 for magnetic-field-induced phase transformation (MFIPT) and consequently magnetic shape memory effect was figured out. Furthermore, the decrease in martensitic transformation temperatures by magnetic fields and almost fully reversible MFIPT from martensite to austenite were confirmed in the alloys within this composition range. [ABSTRACT FROM AUTHOR]

The magnetic state of the low-temperature martensite in a Ni43.5Co6.5Mn39Sn11 magnetic shape memory alloy (MSMA) is disclosed. At temperatures (T) above a critical temperature Tf, the magnetization versus field [M(H)] curves display a sigmoid shape, show no magnetic hysteresis, and can be well fitted according to the Langevin model, confirming that the martensite shows superparamagnetic behavior at T>Tf. On the other hand, the observation of a memory effect during the stop-and-wait protocol and the analysis of dynamic magnetic properties probed by ac susceptibility measurements unequivocally corroborate the superspin glass behavior of interacting magnetic clusters at Tf. The present study provides significant insights into the magnetism of martensite in MSMAs. [ABSTRACT FROM AUTHOR]

The temperature dependence of microwave properties—relaxation frequency and Henry factor—of undoped and p-type doped ten InAs/GaAs quantum-dot layer lasers is reported in the 20–80 °C range. It is shown that the linewidth enhancement factor of the p-type doped devices is temperature insensitive while that of the undoped lasers shows a strong dependence for temperatures above 40 °C. [ABSTRACT FROM AUTHOR]

The authors report a study of the linear electro-optic coefficient in waveguides containing InGaAs/GaAs quantum dots with a band gap at 1.3 μm. The Pockels effect is investigated in the 1.55 μm telecommunication window. The measured linear electro-optic coefficient for InGaAs/GaAs is ∼3.4×10-11 m/V, much higher than that of the bulk or quantum well material. An ∼35% enhancement of the phase variation is achieved compared to that obtained in bulk GaAs waveguides. Finally, a spectral bandwidth of ∼100 nm is demonstrated in the 1.5–1.6 μm window. [ABSTRACT FROM AUTHOR]

Dynamic measurements of the Henry factor αH of InAs/GaAs Fabry-Pérot lasers are compared for 3-, 5- and 10-QD layers. While αH dramatically increases with the bias current for 3- and 5-QD stacks, it only amounts to <4 for the 10-layer stack at high currents, a value similar to that of QW-lasers. [ABSTRACT FROM AUTHOR]

The authors report the growth of 6-, 9-, and 12-layer InAs/InP quantum-dash-in-a-well (DWELL) laser structures using gas source molecular beam epitaxy. Broad area laser performance has been investigated as a function of number of layers. The highest modal gain at 48 cm-1 is achieved for an optimized nine-DWELL layer structure. The effect of layer stacking and p-type doping on the characteristic temperature is also reported. Nine-DWELL layer single mode ridge waveguide lasers showed high slope efficiency (0.2 W/A per facet) and output power (Pout=20 mW), close to those of conventional quantum well devices. [ABSTRACT FROM AUTHOR]

The crystal structures, magnetic structures, and phase transformation of the off-stoichiometric Ni53Mn25Ga22 were studied by neutron powder diffraction at different temperatures. It is shown that Ni53Mn25Ga22 has a tetragonal I4/mmm structure from 20 K to 403 K. An abrupt jump in unit-cell volume around room temperature, corresponding to an endothermic peak in the differential scanning calorimetry curve, was observed. This indicates a pretransformation in the martensitic phase of Ni53Mn25Ga22, which is completely different from the phase transformation in the stoichiometric Ni2MnGa. The sequence of structural transformation in Ni53Mn25Ga22 is closely related to its intrinsic temperature-dependent magnetic structure. [ABSTRACT FROM AUTHOR]

The potential of an InGaAs/GaAs quantum-dot-based phase modulator for broadband (>100 nm) applications at 1.55 µm is demonstrated. A ∼35% enhancement of the phase variation (Vπ ∼ 3.5 V for 4 mm-long devices) is achieved compared to that obtained with bulk GaAs waveguides. [ABSTRACT FROM AUTHOR]

A ferromagnetic shape-memory alloy Ni48Mn25Ga22Co5 was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110)[112-1] and (001)[100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni48Mn25Ga22Co5 is controlled mainly by intergranular mode [ABSTRACT FROM AUTHOR]