Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

http://absimage.aps.org/image/MAR11/MWS_MAR11-2010-000594.pdf

Robust isothermal electric control of exchange bias at room temperature

Tunable electronic and magnetic properties of graphene/carbon-nitride van der Waals heterostructures

By employing first-principles calculations within the framework of density functional theory, we investigated the structural, electronic, and magnetic properties of graphene and various two-dimensional carbon-nitride (2DNC) nanosheets. The different 2DCN gives rise to diverse electronic properties such as metals ( C 3 N 2), semimetals ( C 4 N and C 9 N 4), half-metals ( C 4 N 3), ferromagnetic-metals ( C 9 N 7), semiconductors ( C 2 N, C 3 N, C 3 N 4, C 6 N 6, and C 6 N 8), spin-glass semiconductors ( C 10 N 9 and C 14 N 12), and insulators ( C 2 N 2). Furthermore, the effects of adsorption and substitution of hydrogen atoms as well as N-vacancy defects on the electronic and magnetic properties are systematically studied. The introduction of point defects, including N vacancies, interstitial H impurity into graphene and different 2DCN crystals, results in very different band structures. Defect engineering leads to the discovery of potentially exotic properties that make 2DCN interesting for future investigations and emerging technological applications with precisely tailored properties. These properties can be useful for applications in various fields such as catalysis, energy storage, nanoelectronic devices, spintronics, optoelectronics, and nanosensors.

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Two-dimensional carbon nitride (2DCN) nanosheets: Tuning of novel electronic and magnetic properties by hydrogenation, atom substitution and defect engineering

Integration of graphene-based two-dimensional materials is essential for nanoelectronics applications. Using density-functional theory, we systematically investigate the electronic properties of vertically stacked graphene-graphitic carbon nitrides (GE/GCN). We also studied the covalently lateral stitched graphene-graphitic carbon nitrides (GE-GCN heterojunctions). The effects of perpendicular electric field on the electronic properties of six different heterostructures, i.e., (i) one layer of GE on top of a layer of ${\mathrm{C}}_{n}{\mathrm{N}}_{m}$ with $(n,m)=(3,1)$, (3,4), and (4,3) and (ii) three heterostructures ${\mathrm{C}}_{n}{\mathrm{N}}_{m}/{\mathrm{C}}_{{n}^{\ensuremath{'}}}{\mathrm{N}}_{{m}^{\ensuremath{'}}}$, where $(n,m)\ensuremath{\ne}({n}^{\ensuremath{'}},{m}^{\ensuremath{'}})$ are elucidated. The most important calculated features are (i) the systems $\mathrm{GE}/{\mathrm{C}}_{3}{\mathrm{N}}_{4}, {\mathrm{C}}_{3}\mathrm{N}/{\mathrm{C}}_{3}{\mathrm{N}}_{4}, \mathrm{GE}\ensuremath{-}{\mathrm{C}}_{3}\mathrm{N}, \mathrm{GE}\ensuremath{-}{\mathrm{C}}_{4}{\mathrm{N}}_{3}$, and ${\mathrm{C}}_{3}\mathrm{N}\ensuremath{-}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$ exhibit semiconducting characteristics having small band gaps of ${\mathrm{\ensuremath{\Delta}}}_{0}=20$, 250, 100, 100, 80 meV, respectively while (ii) the systems $\mathrm{GE}/{\mathrm{C}}_{4}{\mathrm{N}}_{3}, {\mathrm{C}}_{3}\mathrm{N}/{\mathrm{C}}_{4}{\mathrm{N}}_{3}$, and ${\mathrm{C}}_{3}\mathrm{N}\ensuremath{-}{\mathrm{C}}_{4}{\mathrm{N}}_{3}$ show ferromagnetic-metallic properties. In particular, we found that, in semiconducting heterostructures, the band gap increases nontrivially with increasing the absolute value of the applied perpendicular electric field. This work is useful for designing heterojunctions and heterostructures made of graphene and other two-dimensional materials such as those proposed in recent experiments [X. Liu and M. C. Hersam Sci. Adv. 5, 6444 (2019)].

Tuning the electronic properties of graphene–graphitic carbon nitride heterostructures and heterojunctions by using an electric field

Metal free half-metallicity has been the subject of intense research in the field of spintronics devices. Using density functional theoretical calculations, atomically thin graphitic heptazine carbon nitride (gh-C3N4) based systems are studied for possible spintronics application. Ferromagnetism is observed in all of the C-doped gh-C3N4 systems due to hole injection. However, a high energy phase of C-doped gh-C3N4 (CN2@gh-C3N4) shows strong half-metallicity with a Curie temperature as high as ∼400 K. The calculated Curie temperature is noticeably higher than the metal-free based half-metallic systems studied to date. Thereby, such a ferromagnetic half-metallic system with a high Curie temperature can be promising for high temperature spintronics applications.

Metal-free half-metallicity in a high energy phase C-doped gh-C3N4 system: a high Curie temperature planar system

Aqueous-phase oxygen evolution reaction (OER) is the bottleneck of water splitting. The formation of the O-O bond involves the generation of paramagnetic oxygen molecules from the diamagnetic hydroxides. The spin configurations might play an important role in aqueous-phase molecular electrocatalysis. However, spintronic electrocatalysis is almost an uncultivated land for the exploration of the oxygen molecular catalysis process. Herein, we present a novel magnetic FeIII site spin-splitting strategy, wherein the electronic structure and spin states of the FeIII sites are effectively induced and optimized by the Jahn-Teller effect of Cu2+. The theoretical calculations and operando attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR) reveal the facilitation for the O-O bond formation, which accelerates the production of O2 from OH- and improves the OER activity. The Cu1-Ni6Fe2-LDH catalyst exhibits a low overpotential of 210 mV at 10 mA cm-2 and a low Tafel slope (33.7 mV dec-1), better than those of the initial Cu0-Ni6Fe2-LDHs (278 mV, 101.6 mV dec-1). With the Cu2+ regulation, we have realized the transformation of NiFe-LDHs from ferrimagnets to ferromagnets and showcase that the OER performance of Cu-NiFe-LDHs significantly increases compared with that of NiFe-LDHs under the effect of a magnetic field for the first time. The magnetic-field-assisted Cu1-Ni6Fe2-LDHs provide an ultralow overpotential of 180 mV at 10 mA cm-2, which is currently one of the best OER performances. The combination of the magnetic field and spin configuration provides new principles for the development of high-performance catalysts and understandings of the catalytic mechanism from the spintronic level.

Regulating the Spin State of FeIII Enhances the Magnetic Effect of the Molecular Catalysis Mechanism.

The design and synthesis of novel energetic compounds with integrated properties of high density, high energy, good thermal stability and sensitivities is particularly challenging due to the inherent contradiction between energy and safety for energetic compounds. In this study, a novel structure of 4-amino-7,8-dinitropyrazolo-[5,1-d] [1,2,3,5]-tetrazine 2-oxide (BITE-101) is designed and synthesized in three steps. With the help of the complementary advantages of different explosophoric groups and diverse weak interactions, BITE-101 is superior to the benchmark explosive HMX in all respects, including higher density of 1.957 g·cm-3, highest decomposition temperature of 295 °C (onset) among CHON-based high explosives to date and superior detonation velocity and pressure (D: 9314 m·s-1, P: 39.3 GPa), impact and friction sensitivities (IS: 18 J, FS: 128 N), thereby showing great potential for practical application as replacement for HMX, the most powerful military explosive in current use. 

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Tri-explosophoric groups driven fused energetic heterocycles featuring superior energetic and safety performances outperforms HMX

Because of the observation of half-metallicity in graphitic carbon nitride C4N3 (g-C4N3), extensive research has recently been focused on this compound. Using density-functional calculations, herein diverse electronic properties of g-C4N3 were engineered by applying biaxial compressive strain. The calculated results demonstrate that g-C4N3 preserves ferromagnetic half-metallicity when the strain is lower than −2%, accompanied by a decrease of the half-metallic gap. When the compressive strain ranges from −5 to −3%, the compound turns into nonmagnetic metal. By increasing the strain on the end, it becomes a nonmagnetic semiconductor. Further investigations show that all nonmagnetic semiconductors possess a direct band gap with a value of around 1.6 eV. This fact indicates that g-C4N3 can be applied in spintronic or photovoltaic fields under a strain environment.

https://iopscience.iop.org/article/10.1088/0022-3727/49/29/295301/pdf

Jie Li

Papers

Regulating the Spin State of FeIII Enhances the Magnetic Effect of the Molecular Catalysis Mechanism.

Tri-explosophoric groups driven fused energetic heterocycles featuring superior energetic and safety performances outperforms HMX

The diverse electronic properties of C4N3 monolayer under biaxial compressive strain: a theoretical study