To run into different usage scenarios, tremendous kinds of bending sensors based on resistive, capacitive, piezoelectric responses, or optical theories have been prepared, which encompass a broad scope of novel materials, such as carbon nanotubes, metallic nanowires, carbonized silk fabrics, and fiber-optics, etc. [7][8][9][10] Despite those impressive performances, the development of novel flexible materials that possess multimodal sensing capabilities for the simultaneous detection of bending curvature and position information remains challenging, which is very critical in novel adhesion-free flexible sensing systems. [11,12] Flexible magnetic films have great potential for wireless multimodal flexible sensor due to the curvature and azimuth angle dependent magnetic anisotropy. [13][14][15][16] Former studies have introduced the sensing functions like correcting localization of the plastic deformation on the sample surface. [17,18] To realize the bending sensing function, ferromagnetic resonance has been reported as an effective sensing technology due to the strong correlation between mechanical bending and magnetic anisotropy. [19] In addition, the microwave absorption performance endows it with great potential in wireless sensing. [20] For instance, Figure 1a shows the 1D sensing relationship between bending curvature radius R and ferromagnetic resonance field (H r ) for flexible high-quality epitaxial Flexible materials and devices that can simultaneously reflect multimodal information are highly desired for novel flexible electronics and intelligent flexible sensing systems. In this regard, flexible magnetic films have great potential for wireless multimodal flexible sensor due to the curvature and azimuth angle-dependent ferromagnetic resonance. However, a key challenge now is to build the precise relationship among the mechanical bending, azimuth angle, and the ferromagnetic resonance of the film, which involves multi-physics and coupled process. In this work, the physical problem is solved by combining material engineering and machine learning. Material domain engineering is applied to form localized multi-peak ferromagnetic resonance features for increasing sensitivity. Besides, convolutional neural network algorithm is utilized to help recognize the bending and azimuth angle modulated ferromagnetic resonance in flexible film systems. It is found that the bending information for the flexible film with engineered domain structure can be mapped to the ferromagnetic profile with accuracy over 99%, while the accuracy sharply decreases to less than 50% in the control group of high-quality film. This study provides a versatile platform for developing machine learning-based novel sensing materials.
The micrometer-sized nickelate–titanate heterojunctions with LaNiO3 (LNO) electrode have been fabricated to investigate the dominant current transport mechanisms under positive and negative bias. The LNO/SmNiO3 (SNO)/Nb:SrTiO3 (NSTO) heterojunction exhibits a highly rectifying feature with a very low leakage in a broad temperature region (from 200 to 425 K), which is attributed to the formation of a Schottky-like barrier at the SNO/NSTO interface. In addition, it is found that the trap defects (i.e., oxygen vacancies) play an essential role in determining the current density ( J) –voltage ( V) characteristics irrespective of the voltage polarity. The leakage current at low electric fields (<0.25 MV/cm) is dominated by temperature-enhanced trap assisted tunneling process, which is caused by the interface oxygen vacancy induced states. Further analysis suggests that, at high fields (>1.2 MV/cm), the leakage is ascribed to the bulk-limited field enhanced thermal ionization of trapped carriers in the SNO film (i.e., Poole–Frenkel emission). Specially, the oxygen vacancy redistribution near the SNO/NSTO heterointerface driven by a high temperature (425 K) or high electrical field (>3.8 MV/cm) stress is emphasized to account for the transition from the Schottky contact limited to bulk-limited conduction mechanism (i.e., space charge limited conduction). This work will benefit the further analysis of the resistive switching phenomena in nickelate-based devices, showing a potential for nonvolatile memory applications.
Magnetoresistance based information devices have attracted much attention due to the ability to utilize spins as information carriers. To promote the magnetoresistance-based devices, ultrahigh magnetoresistance ratios are highly desirable for magnetic sensing, memory, and artificial intelligent devices, etc. However, today the magnetoresistance devices are facing the challenge of limited magnetoresistance ratio, low work temperature, or high magnetic field, which calls for proper theories and mechanisms. To address it, we first introduce the flexible bending-controlled magnetoresistance device based on the La0.67Ba0.33MnO3 film. Due to the anisotropic resistance of the La0.67Ba0.33MnO3 film and the nonlinear amplification effect of the Zener diode, the device has exhibited strong magnetoresistive performance (∼8725% at 1 T, 300 K). Combining the assist from mechanical bending and diode, high magnetic field sensitivity with large magnetoresistance ratio (∼1.7 × 104% at 1 T, 300 K) and low work current (∼0.15 mA) is simultaneously achieved at room temperature, which is over 104 times larger than that of the planar La0.67Ba0.33MnO3 film. Based on the above results, we propose one but not the only possible application as tunable multistage switch. Our findings may pave a strategy to develop flexible diode-enhanced magnetoresistance device with ultrahigh magnetoresistance ratios and bending tunable performances.
In this work, the resistive switching and electrical-control of magnetization in Pt/CoFe2O4/Nb:SrTiO3 heterostructures have been investigated. The films exhibit a classic bipolar resistive switching effect with a maximum switch ratio of about 5 × 103 and good anti-fatigue performance. Associated with resistive switching, the saturated magnetization of the thin film at high resistance state is found to be larger than that at low resistance state. Meanwhile, polarized neutron reflectivity of the thin film under different resistance states was in situ measured. The results reveal that the interfacial migration of oxygen vacancies driven by an applied electric field plays an important role in the modulation of resistive and magnetism of CoFe2O4 resistive switching devices.
Focused helium ion bombardment provides an effective means to modify the properties of ferroelectric materials. This work systematically investigates the effect of helium ion bombardment on the structural, ferroelectric, and dielectric properties of relaxor BaHf0.17Ti0.83O3 thin films at different bombardment doses in the range of 1 × 1012 to 7 × 1015 ions/cm2. The films show more defects and slightly expanded out-of-plane lattice parameters with an increase in dose. Despite helium ion bombardment introducing more defects and structural disorder in the system, the bombardment-induced dipole polarization leads to enhanced ferroelectricity. Our findings highlight energetic helium ion bombardment as an effective way to enhance the ferroelectricity of relaxor materials.
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