J. R. Sun

A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3.

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO(3) and SrTiO(3), provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm(2) V(-1) s(-1) (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO(3) and a spinel γ-Al(2)O(3) epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite two-dimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices.

Giant reversible magnetocaloric effect in metamagnetic HoCuSi compound

The magnetic properties and magnetocaloric effect (MCE) of antiferromagnetic HoCuSi compound have been studied. It is found that HoCuSi undergoes a field-induced first order metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) states below the Neel temperature (TN). A giant MCE without hysteresis loss is observed in HoCuSi around TN. The maximal magnetic entropy change (−ΔSM) and refrigerant capacity are 33.1 J/kgK and 385 J/kg, respectively, for a field change of 0–5 T. The excellent magnetocaloric properties can result from the field-induced AFM-FM transition below TN and the increase in magnetization change caused by the change in lattice volume at TN.

Large reversible magnetocaloric effect caused by two successive magnetic transitions in ErGa compound

Intermetallic compound ErGa exhibits two successive magnetic transitions: spin-reorientation transition at TSR=15 K and ferromagnetic-paramagnetic transition at TC=30 K. Both transitions contribute greatly to the magnetic entropy change (ΔSM), each yielding a significant peak on their ΔSM-T curve and thus a considerable value of refrigerant capacity (RC) without hysteresis loss. For a magnetic field change of 5 T, the maximal values of −ΔSM are 21.3 J/kg K at TC and 16.5 J/kg K at TSR, with an RC value of 494 J/kg. Large reversible magnetocaloric effect and RC indicate the potentiality of ErGa as a candidate magnetic refrigerant at low temperatures.

Large reversible magnetocaloric effects in ErFeSi compound under low magnetic field change around liquid hydrogen temperature

Magnetic properties and magnetocaloric effects (MCEs) of ternary intermetallic ErFeSi compound have been investigated in detail. It is found that ErFeSi exhibits a second-order magnetic transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 22 K, which is quite close to the liquid hydrogen temperature (20.3 K). A thermomagnetic irreversibility between zero-field-cooling and field-cooling curves is observed below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. For a magnetic field change of 5 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 23.1 J/kg K and 5.7 K, respectively. Particularly, the values of −ΔSM and refrigerant capacity reach as high as 14.2 J/kg K and 130 J/kg under a magnetic field change of 2 T, respectively. The large MCE without hysteresis loss for relatively low magnetic field change suggests that ErFeSi compound could be a promising material for magnetic refrigeration...

Large magnetic refrigerant capacity in Gd71Fe3Al26 and Gd65Fe20Al15 amorphous alloys

Magnetic entropy change and refrigerant capacity of Gd-based amorphous Gd71Fe3Al26 and Gd65Fe20Al15 alloys are investigated. The refrigerant capacities reach 750 and 726 J kg−1 for Gd71Fe3Al26 and Gd65Fe20Al15, respectively, which are much larger than those of all magnetocaloric materials ever reported. The peak values of magnetic entropy change under a field change of 0–5 T are 7.4 J kg−1 K−1 at 117.5 K and 5.8 J kg−1 K−1 at 182.5 K for Gd71Fe3Al26 and Gd65Fe20Al15, respectively. A very large refrigerant capacity and a considerable magnetic entropy change jointly make them attractive candidates for magnetic refrigerant.

Good rectifying characteristic in p-n junctions composed of La0.67Ca0.33MnO3-δ/Nb-0.7 wt%-doped SrTiO3

Simple p–n junctions have been fabricated using a simple heteroepitaxial structure of La0.67Ca0.33MnO3−δ/Nb-doped SrTiO3. In such junctions, the La0.67Ca0.33MnO3−δ exhibits semiconductor behavior due to oxygen deficiency, whereas the Nb–0.7 wt %-doped SrTiO3 shows a metal behavior. These junctions demonstrate good rectifying characteristic in a wide temperature range from 5 to 350 K. An intriguing observation is that the rectifying behavior is nearly independent of temperature.

Magnetic properties and magnetocaloric effects in R3Ni2 (R = Ho and Er) compounds

Magnetic and magnetocaloric properties of R3Ni2 (R = Ho and Er) compounds have been investigated. Both Ho3Ni2 and Er3Ni2 compounds undergo two successive phase transitions: spin reorientation transition and second-order ferromagnetic-paramagnetic transition. The maximal values of magnetic entropy change are achieved to be 21.7 J kg−1 K−1 for Ho3Ni2 and 19.5 J kg−1 K−1 for Er3Ni2 for a field change of 0-5 T. A large refrigerant capacity (RC) of 496 J kg−1 in the composite material is also obtained. Large reversible magnetocaloric effect and RC indicate the potentiality of R3Ni2 (R = Ho and Er) compounds as candidates for low-temperature magnetic refrigerant.

Particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2 first‐order systems

Here, we report particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2. Hysteresis loss was getting smaller with reducing the particle size. The reduced ratio can be as high as ∼61% as the sample is ground from bulk into small particles (20‐50 μm). Such reduction can be ascribed to the notably increased surface area of sample and the partially removed internal strain and grain boundaries, other than nucleation factors and electronic band structure. Meanwhile, entropy change |ΔS| slightly decreases, but the effective refrigeration capacity shows an increase due to the notable reduction of hysteresis loss. Our investigations also reveal particle size limitation. When the size is below 10 μm (average ∼ 4 μm), the sample may lose its stability and the |ΔS| notably reduces.

Skin-inspired highly stretchable and conformable matrix networks for multifunctional sensing

Mechanosensation electronics (or Electronic skin, e-skin) consists of mechanically flexible and stretchable sensor networks that can detect and quantify various stimuli to mimic the human somatosensory system, with the sensations of touch, heat/cold, and pain in skin through various sensory receptors and neural pathways. Here we present a skin-inspired highly stretchable and conformable matrix network (SCMN) that successfully expands the e-skin sensing functionality including but not limited to temperature, in-plane strain, humidity, light, magnetic field, pressure, and proximity. The actualized specific expandable sensor units integrated on a structured polyimide network, potentially in three-dimensional (3D) integration scheme, can also fulfill simultaneous multi-stimulus sensing and achieve an adjustable sensing range and large-area expandability. We further construct a personalized intelligent prosthesis and demonstrate its use in real-time spatial pressure mapping and temperature estimation. Looking forward, this SCMN has broader applications in humanoid robotics, new prosthetics, human–machine interfaces, and health-monitoring technologies.Electronic skins have been developed to emulate human sensory systems, but simultaneous detection of multiple stimuli remains a big challenge due to coupling of electronic signals. Here, Hua et al. overcome this problem in a stretchable and conformable matrix network integrated with seven different modes.

Oxygen vacancies induced switchable and nonswitchable photovoltaic effects in Ag/Bi0.9La0.1FeO3 /La0.7Sr0.3MnO3 sandwiched capacitors

The short circuit photocurrent (I-sc) was found to be strongly dependent on the oxygen vacancies (V-Os) distribution in Ag/Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 heterostructures. In order to manipulate the V-Os accumulated at either the Ag/Bi0.9La0.1FeO3 or the Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 interface by pulse voltages, switchable or nonswitchable photocurrent can be observed without or with changing the polarization direction. The sign of photocurrent could be independent of the direction of polarization when the variation of diffusion current and the modulation of the Schottky barrier at the Ag/Bi0.9La0.1FeO3 interface induced by oxygen vacancies are large enough to offset those induced by polarization. Our work provides deep insights into the nature of photovoltaic effects in ferroelectric films, and will facilitate the advanced design of switchable devices combining spintronic, electronic, and optical functionalities