L. Y. Wang

Integrated digital inverters based on two-dimensional anisotropic ReS2 field-effect transistors

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS2) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼107) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.

Study of uniaxial magnetism and enhanced magnetostriction in magnetic-annealed polycrystalline CoFe2O4

Magnetic and magnetostrictive properties of magnetic-annealed polycrystalline CoFe2O4 were investigated. The magnetic hysteresis loops showed obvious uniaxiality with an induced easy direction parallel to the annealing field. Magnetic force microscopy study revealed that the domains were fixed by magnetic annealing. The uniaxial behavior was also observed in the magnetostrictive measurement, which showed a significantly enhanced magnetostriction of − 273 PPM when the external field was applied perpendicular to the annealing field direction. A physical mechanism for the effect of magnetic annealing on polycrystalline CoFe2O4 is developed, in which the induced uniaxiality is ascribed to the realignment of easy axes in polycrystals. The uniaxial behavior of magnetism and enhanced magnetostriction could be well explained by this model.

Investigation of the intermediate phase and magnetocaloric properties in high-pressure annealing Ni–Mn–Co–Sn alloy

The Ni–Mn–Co–Sn alloy is prepared by high-pressure annealing method. Besides the enhanced martensitic transformation temperature and the Curie temperature of austenite, an intermediate phase above the martensitic transformation is observed in this alloy. As a result, two successive magnetic entropy changes with the same sign are obtained around room-temperature, corresponding to the martensitic transformation and intermediate phase transition, respectively. The origin of the intermediate phase for high-pressure annealing Ni–Mn–Co–Sn alloy is discussed.

Large converse magnetoelectric effect in Metglas FeCoBSi and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite

Converse magnetoelectric (CME) effect is investigated in a FeCoBSi/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite by using induction method within different frequencies. A large CME coefficient of 3.05 G/V is observed at the resonance frequency of 76.5 kHz under a low bias magnetic field of 50 Oe. The CME coefficient of the heterostructure is almost constant and exhibits a relatively high value in a wide frequency span of 1–64 kHz. The origin of large CME effect and the advantages of Metglas acting as ferromagnetic layer are discussed in the present paper.

Electric field control of magnetic properties in CoPt/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature

We demonstrate an obvious electric-field control of magnetic properties in CoPt/PMN-PT heterostructure at room temperature. Not only the remanent magnetization but also the coercivity exhibits an obvious response with the electric field. Without the aid of magnetic bias field, the remanent magnetization of the CoPt film shows an analogous on-off behavior with the electric field switching on and off alternatively. The magnetization reversal can be electrically controlled in this heterostructure due to the variation of coercivity caused by electric field.

Electric field control of magnetism without magnetic bias field in the Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite

This paper reports on the electric field control of magnetism without magnetic bias field in a Ni/Pb(Mg1/3Nb2/3)O3-PbTiO3/Ni composite prepared by electrochemical deposition. The converse magnetoelectric effect, which was measured by an induction method, shows a peak value of 0.45 G/V at the resonance frequency of 102 kHz. Without magnetic bias field, the magnetization of the Ni layers can be controlled by an applied dc electric field in a reversible and reproducible way and shows an analogous on-off behavior with the electric field switching on and off alternatively.

Giant magnetocaloric and magnetoresistance effects in ferrimagnetic Mn1.9Co0.1Sb alloy

Magnetic and transitional behaviors are investigated in Mn1.9Co0.1Sb intermetallic compound. Mn2Sb is a simple ferrimagnet with Neel temperature around 550 K. The Co-introduction results in the appearance of antiferromagnetic state, and therefore, the first-order magnetic transition occurs between antiferromagnetic and ferrimagnetic state, which can be induced by temperature/magnetic field, in Mn1.9Co0.1Sb alloy. Accordingly, a magnetic entropy change as high as 5 J kg−1 K−1 and a large magnetoresistance of 46% under the field change of 10 and 50 kOe are achieved, respectively.

The electric field manipulation of magnetization in La1−xSrxCoO3/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures

La1−xSrxCoO3 (x = 0.18, 0.33, and 0.5) films were grown epitaxially on piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrates by pulsed laser deposition. The magnetization of these films varies with the external electric field, showing the magnetoelectric effect. With different doping content of Sr2+ ions, the change of magnetization for these films show different behaviors with increasing temperature, which can be attributed to the competition between electric-field-induced changes of spin state and double exchange interaction. This work presents an alternative mechanism to investigate the electric field control of magnetism in magnetoelectric heterostructure by tuning the spin state.

Atomic Layer Deposited Oxide-Based Nanocomposite Structures with Embedded CoPtx Nanocrystals for Resistive Random Access Memory Applications

Al2O3- or HfO2-based nanocomposite structures with embedded CoPtx nanocrystals (NCs) on TiN-coated Si substrates have been prepared by combination of thermal atomic layer deposition (ALD) and plasma-enhanced ALD for resistive random access memory (RRAM) applications. The impact of CoPtx NCs and their average size/density on the resistive switching properties has been explored. Compared to the control sample without CoPtx NCs, ALD-derived Pt/oxide/100 cycle-CoPtx NCs/TiN/SiO2/Si exhibits a typical bipolar, reliable, and reproducible resistive switching behavior, such as sharp distribution of RRAM parameters, smaller set/reset voltages, stable resistance ratio (≥102) of OFF/ON states, better switching endurance up to 104 cycles, and longer data retention over 105 s. The possible resistive switching mechanism based on nanocomposite structures of oxide/CoPtx NCs has been proposed. The dominant conduction mechanisms in low- and high-resistance states of oxide-based device units with embedded CoPtx NCs are Ohmic behavior and space-charge-limited current, respectively. The insertion of CoPtx NCs can effectively improve the formation of conducting filaments due to the CoPtx NC-enhanced electric field intensity. Besides excellent resistive switching performances, the nanocomposite structures also simultaneously present ferromagnetic property. This work provides a flexible pathway by combining PEALD and TALD compatible with state-of-the-art Si-based technology for multifunctional electronic devices applications containing RRAM.

Manipulation of magnetic field on dielectric constant and electric polarization in Cr2WO6

The magnetic, dielectric, and magnetoelectric properties are investigated in the polycrystalline Cr2WO6. Under zero magnetic fields, no dielectric anomaly and electric polarization are observed in this compound. After magnetoelectric annealing, the magnetic-field-induced dielectric and pyroelectric current peaks simultaneously present around its Neel temperature and increase with increasing magnetic field, showing large magneto-dielectric and linear magnetoelectric effects in Cr2WO6. The origin of magnetoelectric effect in this compound is discussed.