Chengbao Jiang

Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal ferromagnets

The magnetostructural coupling between the structural and the magnetic transition has a crucial role in magnetoresponsive effects in a martensitic-transition system. A combination of various magnetoresponsive effects based on this coupling may facilitate the multifunctional applications of a host material. Here we demonstrate the feasibility of obtaining a stable magnetostructural coupling over a broad temperature window from 350 to 70 K, in combination with tunable magnetoresponsive effects, in MnNiGe:Fe alloys. The alloy exhibits a magnetic-field-induced martensitic transition from paramagnetic austenite to ferromagnetic martensite. The results indicate that stable magnetostructural coupling is accessible in hexagonal phase-transition systems to attain the magnetoresponsive effects with broad tunability.

Effect of Ni excess on phase transformation temperatures of NiMnGa alloys

A systematic substitution of Ni for Mn, Ga, or both Mn and Ga in the non-stoichiometric NiMnGa alloys is performed. The relationship among the composition, structure and martensitic transformation temperatures was studied in detail for the Ni excessive NiMnGa alloys. The martensitic transformation temperatures almost linearly increase with increasing Ni content in all the three series from lower than 0 °C up to 300 °C. The increases in rate of the martensitic transformation temperatures are different for the three cases. It is large for Ga substituted by Ni, slow for Mn and intermediate for both Mn and Ga. The size factor and electronic concentrations are thought to influence the martensitic transformation temperature in the NiMnGa alloys. The determined relationship will be significant for designing a suitable NiMnGa alloy with a required martensitic transformation temperature for application at a specific temperature.

A high-temperature shape-memory alloy Ni54Mn25Ga21

A high-temperature shape-memory alloy, Ni54Mn25Ga21, was developed with a shape-memory effect of 6.1% and a martensitic transformation temperature higher than 250 °C for single crystals. The measured compressive strength and strain were 845 MPa and 20.5%, respectively, with a compressive axis along the growth direction of the rods at room temperature. One thousand thermal cycles were performed on the Ni54Mn25Ga21 without obvious changes of the martensitic structure, transformation behavior, and shape-memory effect, indicating an excellent thermal stability for the present alloy.

Thermal stability of the Ni54Mn25Ga21 Heusler alloy with high temperature transformation

Abstract Ni 54 Mn 25 Ga 21 is studied with martensitic transformation temperature higher than 250 °C. 1000 thermal cycles are performed without obvious differences of its microstructure and martensitic transformation behavior. The single-phase and the well self-accommodated martensitic twins are thought to be attributed to its high stability of the martensitic transformation.

Giant magnetostrictive actuators for active vibration control

Giant magnetostrictive actuators are designed and fabricated with home-made TbDyFe magnetostrictive rods. The corresponding static and dynamic characteristics are tested. The total output displacement can be obtained up to 100 µm and the output force up to 1500 N. The dynamic responses of input and output are accordant and have a small hysteresis. Experiments on active vibration control are implemented in single-degree-of-freedom (DOF) and six-DOF platforms in a flexible space structure. The excellent damping effect, up to 30 dB, proves the good performance of the actuators, the feasibility of the control algorithms, and the reasonable design of the six-DOF platform.

Half-metallic properties for the Mn2FeZ (Z=Al, Ga, Si, Ge, Sb) Heusler alloys: A first-principles study

The electronic structure and magnetism of the Mn2FeZ (Z=Al, Ga, Si, Ge, Sb) Heusler alloys have been studied by density functional calculations. Two half-metallic ferromagnets, namely, Mn2FeAl and Mn2FeSb, are predicted. It is found that a small expansion of the crystal lattice can restore the half-metallicity in Mn2FeSi. The calculated total magnetic moments Mtot are 1μB/f.u. for Mn2FeAl and Mn2FeGa, 2μB/f.u. for Mn2FeSi and Mn2FeGe, and 3μB/f.u. for Mn2FeSb, which agree with the Slater–Pauling curve quite well. The moments of Mn (A) and Mn (B) are large and antiparallel to each other, which is indicative of ferrimagnetism in Mn2FeZ alloys. Fe shows only a small moment and its moment is parallel to that of Mn (B). By investigating the effect of lattice distortion on the half-metallicity and magnetic moments of Mn2FeZ, it is found that the half-metallic properties of Mn2FeSb are insensitive to the lattice distortion and a 100% spin polarization can be obtained within the wide range of 5.4–6.05 A. This is ...

Superhigh strains by variant reorientation in the nonmodulated ferromagnetic NiMnGa alloys

Superhigh strains of 15% for the Ni53Mn25Ga22 and 13.5% for the Ni54Mn23Ga23 with the nonmodulated martensite structure were achieved by variant reorientation. A strong magnetic anisotropy exists in the prefabricated single variant with the easy axis along the contraction [001] direction of the high-temperature cubic phase. A higher austenitic transformation temperature was found in the single variant comparing with the original multivariant sample. The same order of magnitude for the saturation magnetization Ms, magnetic anisotropy constant ku, and the twin reorientation stress σtw, namely, 57.6 A m2/kg, 1.4×105 J/m3, and approximately 20 MPa, respectively, as those in 5M martensite indicate that it is reasonable to expect a much higher magnetic field-induced-strain in the nonmodulated NiMnGa alloys.

Martensitic transformation and magnetization of Ni-Fe-Ga ferromagnetic shape memory alloys

Abstract It is shown that the martensite start temperature of Ni 2+ x Fe 1− x Ga ferromagnetic shape memory alloys increases with increasing Ni content. The thermal strain due to the reversible martensitic transformation is 0.1%. The Curie temperatures and the saturation magnetization of the alloys increase with increasing Fe content.

Co-occurrence of magnetic and structural transitions in the Heusler alloy Ni53Mn25Ga22

A co-occurrence of magnetic and structural transitions was observed in a nonstoichiometric Ni53Mn25Ga22 alloy which undergoes a reverse martensitic transformation from ferromagnetic martensite to paramagnetic austenite at a magnetic transition temperature (134 °C) higher than the Curie temperature of the stoichiometric Ni2MnGa alloy (103 °C). The effect of the magnetic field on the phase transition temperature was found to be two orders of magnitude greater in the present alloy than in Ni2MnGa due to the absence of the ferromagnetic state in austenite. This may open the possibility of utilizing NiMnGa alloys at a low magnetic field.

Self-Driven Photodetector and Ambipolar Transistor in Atomically Thin GaTe-MoS2 p–n vdW Heterostructure

Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS2 p-n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron-hole pairs are readily separated by large built-in potential formed at the GaTe-MoS2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface.