Eryong Liu

A coupling of martensitic and metamagnetic transitions with collective magneto-volume and table-like magnetocaloric effects

A coupling of the first-order paramagnetic-to-induced-ferromagnetic martensitic and the second-order antiferromagnetic-to-ferromagnetic metamagnetic transitions was found in MnNi0.8Fe0.2Ge alloy. Based on the coupling, a magneto-volume effect driven by the martensitic transition and a table-like magnetocaloric effect generated by the successive magnetic phase transitions arise collectively. By using the magneto-volume effect, the internal stress in the volume-expansion martensitic transition was determined at 350 MPa. The magnetocaloric effect, with a wide working temperature range of 26 K around room temperature, shows a small hysteresis loss (5 J kg−1) and a large net refrigerant capacity (157 J kg−1).

Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi

In this paper, we investigate the half-metallicity of Heusler alloys Fe2Co1-x CrxSi by first principles calculations and anisotropy magnetoresistance measurements. It is found that, with the increase of Cr content x, the Fermi level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of conduction band, and a large half-metallic band gap of 0.75 eV is obtained for x=0.75. We then successfully synthesized a series of Heusler Fe2Co1-x CrxSi polycrystalline ribbon samples. The results of X-ray diffraction indicate that the Fe2Co1-x CrxSi series of samples are pure phase with a high degree of order and the saturation magnetic moment follows half-metallic Slater-Pauling rule. Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic magnetoresistance of Fe2Co1-x CrxSi (x=0.25, 0.5, and 0.75) shows a negative value suggesting they are stable half-metallic ferromagnets

Corrosion inhibition of functional graphene reinforced polyurethane nanocomposite coatings with regular textures

In order to further enhance its anti-corrosion properties as a surface coating for protecting various materials from corrosion, polyurethane (PU) needs to be modified by adjusting the chemical composition and interface structure. In this work, a series of functionalized graphene (FG) reinforced PU nanocomposite coatings with regular texture were fabricated using a replication method. The structural and morphological properties of the as-prepared PU composite coatings were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectrometer, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. Results showed that FG was dispersed homogeneously in the PU matrix after chemical modification. Moreover, the morphology of the obtained coatings showed a circular cone with a diameter of 8 μm spaced 8, 6 and 4 μm apart, respectively. Most importantly, the presence of surface texture and well-dispersed FG effectively enhanced the anti-corrosion properties of the textured FG/PU composite coating. It is attributed to the hydrophobicity and barrier effect of the obtained coatings, which not only reduce the contact and interaction between water and the surfaces, but also increase the tortuosity of the corrosive medium diffusion pathway.

Structural and magnetic properties of MnCo1−xFexSi alloys

Abstract The crystal structures, martensitic structural transitions and magnetic properties of MnCo1−xFexSi (0≤x≤0.50) alloys were studied by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and magnetic measurements. In high-temperature paramagnetic state, the alloys undergo a martensitic structural transitions from the Ni2In-type hexagonal parent phase to the TiNiSi-type orthorhombic martensite. Both the martensitic transition temperature (TM) and Curie temperatures of martensite ( T C M ) decrease with increasing Fe content. The introduced Fe atoms establish ferromagnetic (FM) coupling within Fe-6Mn atom configurations and destroy the double spiral antiferromagnetic (AFM) coupling in MnCoSi compound, resulting in a magnetic change in the martensite phase from a spiral AFM state to an FM state. For the alloys with x=0.10, 0.15 and 0.20, a metamagnetic transition was observed in between the two magnetic states. A magnetostructural phase diagram of MnCo1−xFexSi (0≤x≤0.50) alloys was proposed.

New spin injection scheme based on spin gapless semiconductors: A first-principles study

Spin injection efficiency based on a conventional and/or half-metallic ferromagnet/semiconductor is greatly limited by the Schmidt obstacle due to conductivity mismatch; here we proposed that by replacing the metallic injectors with spin gapless semiconductors can significantly reduce the conductive mismatch to enhance spin injection efficiency. By performing first-principles calculations based on superlattice structure, we have studied a representative system of Mn2CoAl/semiconductor spin injector scheme. The results showed that a high spin polarization was maintained at the interface in systems of Mn2CoAl/Fe2VAl constructed with (100) interface and Mn2CoAl/GaAs with (110) interface, and the latter is expected to possess long spin diffusion length. Inherited from the spin gapless feature of Mn2CoAl, a pronounced dip was observed around the Fermi level in the majority spin density of states in both systems, suggesting fast transport of the low-density carriers.

Effect of Ag2Mo2O7 Incorporation on the Tribological Characteristics of Adaptive Ni-Based Composite at Elevated Temperatures

A high-temperature self-lubricating Ni-based composite was prepared with the addition of Ag2Mo2O7 by a powder metallurgy technique. X-ray diffraction (XRD) analysis showed that Ag2Mo2O7 decomposed to Ag and MoO3 during the sintering process. The tribological properties of Ni-based composites were evaluated, and the effects of Ag2Mo2O7 incorporation on the friction and wear characteristics of composites were analyzed. The results showed that the tribological properties of Ni-based composite deteriorated with increasing temperature, and the addition of Ag2Mo2O7 decreased the coefficient of friction and wear rate of Ni-based composite at medium and high temperatures. The coefficient of friction and wear rate of composite containing 20 wt% Ag2Mo2O7 were lowered to 0.33 and 1.51 × 10−5 mm3 N−1 m−1, respectively. The wear mechanism was characterized by plastic deformation and delamination. In addition, the improvement of tribological properties of the Ni-based composite at high temperatures is attributed to synergistic lubricating effect of silver molybdate (reproduce in the rubbing process at high temperatures) and iron oxide (transfer from disk material to the pin).

Prediction of topological insulating behavior in inverse Heusler compounds from first principles

The topological band structures of the X2YZ Heusler compounds with the Hg2CuTi structure are investigated by using first-principles calculations within density functional theory. Our results clearly show that a large number of the Hg2CuTi type Heusler compounds naturally exhibit distinct band-inversion feature, which is mainly controlled by the Y-Z zinc blende sublattice. Similar to the half-Heusler family, the topological band order in Hg2CuTi type Heusler compounds is sensitive to the variation of lattice constant, and most of them possess a negative formation energy, which makes them more suitable in material growth and could easily achieve the topological insulating behavior by alloying or proper strain.We present extensive first-principles calculations on the inverse full-Heusler compounds having the chemical formula X

Windows open for highly tunable magnetostructural phase transitions

_2

Transition from Anomalous Hall Effect to Topological Hall Effect in Hexagonal Non-Collinear Magnet Mn 3 Ga

YZ where (X = Sc, Ti, V, Cr or Mn), (Z = Al, Si or As) and the Y ranges from Ti to Zn. Several of these alloys are identified to be half-metallic magnets. We show that the appearance of half-metallicity is associated in all cases to a Slater-Pauling behavior of the total spin-magnetic moment. There are three different variants of this rule for the inverse Heusler alloys depending on the chemical type of the constituent transition-metal atoms. Simple arguments regarding the hybridization of the d-orbitals of neighboring atoms can explain these rules. We expect our results to trigger further experimental interest on this type of half-metallic Heusler compounds.

Topological insulators with unexpectedly HgTe-like band inversion in hexagonal wurtzite-type binary compounds

An attempt was made to tailor the magnetostructural transitions over a wide temperature range under the principle of isostructural alloying. A series of wide Curie-temperature windows (CTWs) with a maximal width of 377 K between 69 and 446 K were established in the Mn1−yCoyNiGe1−xSix system. Throughout the CTWs, the magnetic-field-induced metamagnetic behavior and giant magnetocaloric effects are obtained. The (Mn,Co)Ni(Ge,Si) system shows great potential as multifunctional phase-transition materials that work in a wide range covering liquid-nitrogen and above water-boiling temperatures. Moreover, general understanding of isostructural alloying and CTWs constructed in (Mn,Co)Ni(Ge,Si) as well as (Mn,Fe)Ni(Ge,Si) is provided.