Zongyao Li

Reproducible magnetostrain behavior induced by structure transformation for Ni46Co4Mn39Sn11 Heusler alloy

This paper presents the strain behavior associated with martensitic transformation for polycrystalline Ni46Co4Mn39Sn11. The unique reproducible magnetostrain in this alloy has been realized within a magnetic field change of 3 T, and its maximum value achieves about 0.012% at 225 K, which is almost ten times higher than that in Ni-Mn-Sn ternary alloy. Such a reproducible phenomenon could be attributed to the occurrence of the reversible transformation between multi-variant martensite and austenite under an applied isothermal magnetic field.

Tunnel junctions with a ferroelectric-ferromagnetic composite barrier

A theoretical model for a tunnel junction with a ferroelectric-ferromagnetic (insulator) composite barrier separating two metallic electrodes is proposed. By using free electron direct quantum tunneling method and transfer matrix formalism, taking into account screening of polarization charges in metallic electrodes and dielectric response in ferromagnetic barrier, we investigate the spin filtering (SF) effect, tunneling magnetoresistance (TMR), and electroresistance (TER) effects in the junction. It is shown that the large SF effect, hence TMR and TER effects, can be achieved. Eight resistive states in the junction can also be realized by the reversal of electric polarization in the ferroelectric layer and magnetization either in the ferromagnetic layer or in the electrodes.A theoretical model for a tunnel junction with a ferroelectric-ferromagnetic (insulator) composite barrier separating two metallic electrodes is proposed. By using free electron direct quantum tunneling method and transfer matrix formalism, taking into account screening of polarization charges in metallic electrodes and dielectric response in ferromagnetic barrier, we investigate the spin filtering (SF) effect, tunneling magnetoresistance (TMR), and electroresistance (TER) effects in the junction. It is shown that the large SF effect, hence TMR and TER effects, can be achieved. Eight resistive states in the junction can also be realized by the reversal of electric polarization in the ferroelectric layer and magnetization either in the ferromagnetic layer or in the electrodes.

Current localization and enhanced percolative low-field magnetoresistance in disordered half metals

By modeling the magnetotransport in disordered half metals onto a random resistor network, we have performed numerical simulations on the low-field magnetoresistance (LFMR) and the current distribution in the network. It is found that there is a close relationship between the magnitude of LFMR and the current morphology. LFMR increases with the increase of current localization. In the limit of strong disorder, a quasi-one-dimensional transport channel forms and LFMR reaches its maximum. Compared with the previous two-component (metal/insulator) percolative scenario for colossal magnetoresistance in phase-separated manganites, such a current percolation transition gives further understanding of the magnetotransport in disordered half metals.

Magnetostrain and magnetocaloric effect by field-induced reverse martensitic transformation for Pd-doped Ni45Co5Mn37In13 Heusler alloy

In the present work, polycrystalline Ni45Co5−xPdxMn37In13 (x = 0, 0.5, 1, and 3) Heusler alloys were prepared. The influences of Pd substitution for Co on crystal structure, martensitic transformation (MT), and magnetic properties have been carefully investigated for these quinary alloys. The structure measurement indicates that every sample possesses L10 martensitic structure at room temperature. With increasing of Pd content, it is found that the MT region shifts towards higher temperature, but the Curie transition region of austenitic state moves to lower temperature. Owing to the fact that the MT gradually approaches Curie point, the magnetization of austenitic phase is significantly decreased, while the one of martensitic phase almost remains unchanged. In addition, the functional properties associated with the field-induced reverse MT have been also studied in Ni45Co5−xPdxMn37In13 (x = 0, 0.5, and 1) alloys. In comparison to quaternary parent alloy, both of enhanced magnetostrain (0.3%) and isotherm...

The converse piezoelectric effect on electron tunnelling across a junction with a ferroelectric-ferromagnetic composite barrier

A theoretical investigation of the converse piezoelectric effect on electron tunnelling across a tunnel junction with a ferroelectric?ferromagnetic composite barrier is proposed. Transfer matrix calculations show that the spin filtering and tunnelling magnetoresistance may be enhanced or reduced due to the presence of converse piezoelectricity in the ferroelectric barrier, depending on the orientation of the electrical polarization in the barrier relative to the applied field. In addition, the tunnelling electroresistance is found to be significantly changed, not only in magnitude but also in sign. The investigation offers a new route towards controllable spin transport.

Electrically controlled Kerr effect in magnetophotonic crystals based on nematic liquid crystals

An electrically controllable Kerr effect in magnetophotonic crystals consisting of magnetic materials and nematic liquid crystals is presented by considering the properties of nematic liquid crystals. Numerical results show that the Kerr effect is changed remarkably by adjusting the permittivity of liquid crystal, and the maximum value of the Kerr rotation angle is enhanced with the increase in the permittivity of liquid crystal. Such properties demonstrate the possibility of tunable magneto-optical devices based on nematic liquid crystals.

Growth of low-threading-dislocation-density GaN on graphene by hydride vapor phase epitaxy

Recently, gallium nitride (GaN) films grown on graphene have been widely studied. Here, we have grown low-threading-dislocation-density GaN films on graphene by hydride vapor phase epitaxy (HVPE). The full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) of the GaN films were 276 and 350 arcsec at the 0002 and reflections, respectively. This shows that the threading dislocation densities are on the order of magnitude of 108 cm−2, which is consistent with the results of cathodoluminescence (CL).

Converse piezoelectric effect on the electron tunneling across a multiferroic junction

Converse piezoelectric effect on the electron tunneling across a tunnel junction with a multiferroic barrier is investigated theoretically. It is found that the spin filtering, tunnel magnetoresistance (TMR), and tunnel electroresistance (TER) are enhanced (reduced) due to the presence of the strain in the barrier when the electrical polarization is oriented antiparallel (parallel) to the applied field. The TMR and TER can even increase with the increasing applied voltage when the converse piezoelectric effect is very strong in the barrier, which is totally different from the voltage dependence in the junction with the barrier without piezoelectric effect.

Polarization-independent directional anisotropic optical effect in magnetophotonic crystal

Polarization-independent directional anisotropic optical effect, a feature that has not been appreciated in the literature so far, in one dimensional magnetophotonic crystals consisting of ferromagnetic materials and anisotropic dielectric layers with misaligned in-plain anisotropy is investigated. We have known that such a configuration exhibits asymmetric spectrum at the certain frequency region [A. Figotin and I. Vitebskiy, Phys. Rev. B 67, 165210 (2003)]. In this paper, the existence of the directional anisotropic optical effect is examined according to 4×4 Muller matrix method based on the asymmetric properties of the system. Our results show that this effect can be realized in such magnetophotonic crystals without the existence of magnetization and polarization simultaneously. Furthermore, the order of magnitude of this unique electromagnetic effect can be up to 10−3.

Evolution of threading dislocations in GaN epitaxial laterally overgrown on GaN templates using self-organized graphene as a nano-mask

Growth of high-quality GaN within a limited thickness is still a challenge, which is important both in improving device performance and in reducing the cost. In this work, a self-organized graphene is investigated as a nano-mask for two-step GaN epitaxial lateral overgrowth (2S-ELOG) in hydride vapor phase epitaxy. Efficient improvement of crystal quality was revealed by x-ray diffraction. The microstructural properties, especially the evolution of threading dislocations (TDs), were investigated by scanning electron microscopy and transmission electron microscopy. Stacking faults blocked the propagation of TDs, and fewer new TDs were subsequently generated by the coalescence of different orientational domains and lateral-overgrown GaN. This evolution mechanism of TDs was different from that of traditional ELOG technology or one-step ELOG (1S-ELOG) technology using a two-dimensional (2D) material as a mask.