Z.H. Liu

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated. The onset desorption temperature of the LiAlH4 + 2 mol% CoFe2O4 sample is 65 °C, which is 90 °C lower that of the as-received LiAlH4, with approximately 7.2 wt% hydrogen released at 250 °C. The isothermal desorption results show that for the 2 mol% CoFe2O4 doped sample dehydrogenated at 120 °C, 6.8 wt% of hydrogen can be released within 160 min, which is 6.1 wt% higher than that of the as-received LiAlH4 under the same conditions. Through the differential scanning calorimetry (DSC) and the Kissinger desorption kinetics analyses, the apparent activation energy, Ea, of the 2 mol% CoFe2O4 doped sample is calculated as 52.4 kJ mol−1 H2 and 86.5 kJ mol−1 H2 for the first two decomposition processes. This is 42.4 kJ mol−1 H2 and 86.1 kJ mol−1 H2 lower compared with the pristine LiAlH4, respectively, indicating considerably improved dehydrogenation kinetics by doping the CoFe2O4 catalyst in the LiAlH4 matrix. From the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses, a series of finely dispersed Fe and Co species with a range of valence states, produced from the reactions between LiAlH4 and CoFe2O4, play a synergistic role in remarkably improving LiAlH4 dehydrogenation properties. The rehydrogenation properties of the LiAlH4 + 2 mol% CoFe2O4 sample have also been investigated at 140 °C under 6.5 MPa pressure held for 2.5 h.

Micromagnetic simulation of high-power spin-torque oscillator in half-metallic Heusler alloy spin valve nanopillar

We investigated the spin-torque oscillator in a half-metallic Heusler alloy Co2MnSi (CMS) spin-valve nanopillar using micromagnetic simulations. Although it is known that the out-of-plane precession (OPP) usually has a larger power output than the in-plane precession (IPP), only IPP mode was experimentally observed in CMS. Our simulations revealed the fundamental and second harmonic radio frequency (rf) oscillations of the IPP mode, consistent with the experimental measurements in CMS-based pillars. Our simulations predicted that the OPP mode can be obtained under the condition of an initially antiparallel state, a small external magnetic field, and a sufficiently large current density.

Simulation of multilevel cell spin transfer switching in a full-Heusler alloy spin-valve nanopillar

A multilevel cell spin transfer switching process in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar was investigated using micromagnetic simulations. An intermediate state of two-step spin transfer magnetization switching was reported due to the four-fold magnetocrystalline anisotropy; however, we discovered the intermediate state has two possible directions of −90° and +90°, which could not be detected in the experiments due to the same resistance of the −90° state and the +90° state. The domain structures were analyzed to determine the mechanism of domain wall motion and magnetization switching under a large current. Based on two intermediate states, we reported a multilevel bit spin transfer multi-step magnetization switching by changing the magnetic anisotropy in a full-Heusler alloy nanopillar.

Towards fully compensated ferrimagnetic spin gapless semiconductors for spintronic applications

Extensive first-principles calculations suggest that inverse Heusler compounds , , , and are the candidates to achieve fully compensated ferrimagnetic spin gapless semiconductors. It is shown that only the holes can be 100% spin polarized in , while both the excited electrons and the holes around the Fermi level 100% spin polarized in the others. A simple rule for searching potential fully compensated ferrimagnetic spin gapless semiconductors in Heusler compounds is proposed. Due to the spin gapless semiconducting and the fully compensated ferrimagnetic properties, these compounds offer distinct advantage towards the development of the practical spintronic devices.

Modelling current-induced magnetization switching in Heusler alloy Co2FeAl-based spin-valve nanopillar

We investigated the current-induced magnetization switching in a Heusler alloy Co2FeAl-based spin-valve nanopillar by using micromagnetic simulations. We demonstrated that the elimination of the intermediate state is originally resulted from the decease of effective magnetic anisotropy constant. The magnetization switching can be achieved at a small current density of 1.0 × 104 A/cm2 by increasing the demagnetization factors of x and y axes. Based on our simulation, we found magnetic anisotropy and demagnetization energies have different contributions to the magnetization switching.

Observation of weak antilocalization effect in high-quality ScNiBi single crystal

In this paper, we have successfully grown the high-quality ScNiBi single crystals by a Bi flux method and investigated their electronic-transport properties. It was found that the ScNiBi single crystal is a gapless semiconductor with positive linear magnetoresistance (MR). Moreover, the field-dependent MR in the low-field region has demonstrated obvious weak antilocalization (WAL) effect below 50 K. The extremely large prefactor α and angle-dependent magnetoconductance ΔGxx suggest that the WAL effect originates from the contribution of a strong bulk spin-orbital coupling.

A thermodynamic potential for Ni45Co5Mn36.7In13.3 single crystal

A thermodynamic potential as a function of the ferromagnetic, antiferromagnetic, and martensite order parameters is developed using existing experimental data. It successfully reproduces the single domain properties of Ni45Co5Mn36.7In13.3 bulk crystal, including the Curie temperature, the transition temperature from ferromagnetic austenite phase to antiferromagnetic martensite phase as well as its response to an externally applied magnetic field, the saturated magnetization, the martensite strain, the entropy change, and the magnetic permeability. It can be applied to explore the stress-strain and magnetic field-strain behaviors and implemented in phase field simulations to study the ferromagnetic, antiferromagnetic, and martensite domain stability and evolution.

Cycling Stability Performance of La0.75Mg0.25Ni3.5Si0.10 Hydrogen Storage Alloy in Discharge–Charge System

La0.75Mg0.25Ni3.5Si0.10 hydrogen storage alloy was prepared by vacuum induction melting furnace and subsequently heated treatment at 940°C for 8 h and cooled to room temperature in the oven. The electrochemical properties of La0.75Mg0.25Ni3.5Si0.10 compound were measured by LAND CT2001A battery test system. The morphologies of the samples were characterized by scanning electron microscopy (SEM). The surface state of samples was analyzed by X-ray photoelectron spectroscopy (XPS). It was found that the charge–discharge rate plays the key impact on the cycling stability of the alloy. During the cycle test, the prepared La0.75Mg0.25Ni3.5Si0.10 compound presented an excellent capacity retention at the charge–discharge of 1 C while the capacity of sample declined rapidly at 0.2 C. The excellent cycling stability performance of La0.75Mg0.25Ni3.5Si0.10 electrode at 1 C could be attributed to the less powder and less oxidation of surface effective active elements. The pulverization inevitably leads to the separation of the part of the cracking alloy and the electrode, resulting in reduction of the effective active substance and increasing attenuation of the capacity per cycle. In addition, on the analysis of the different cut-off potential effects on the electrode, it was found that the La0.75Mg0.25Ni3.5Si0.10 electrode shows good comprehensive electrochemical properties at 1 C cut-off 0.6–0.7 V. During charging, heavy overcharge will not be conducive to cycling stability performance during the charging test.