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Here, we report the growth of (Sr, Ca) Nd2Fe2O7 single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 103 Hz in a 1 T magnetic field, can be obtained in a SrNd2Fe2O7 crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and 57Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd2Fe2O7 can be attributed to polaronic hopping between two neighboring Fe3+ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd2Fe2O7 is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd2Fe2O7 crystals at room temperature can be used in magneto-dielectric controlled devices. [ABSTRACT FROM AUTHOR]

We attempt to modify the magnetoelectric properties of antiferromagnetic Bi2Fe4O9 nanograins by substituting multivalent Mn ions at Fe sites. The doped Bi2Fe4O9 nanograins are synthesized by a hydrothermal method with a different Mn content x (x is the mole ratio of Mn to Mn plus Fe; x = 0.00, 0.02, 0.04, 0.06, and 0.10). Among them, the x = 0.04 sample shows the anomalous decrease of lattice parameters a and b, the lowest antiferromagnetic transition temperature, and the largest saturated magnetization. Besides, the magneto-dielectric effect (Δɛ/ɛ ∼ −4.9%) and the magneto-striction constant (λ ∼ −1.1 × 10−4) of the x = 0.04 sample are also the largest compared with others (220 K and 0.6 T). Combined with Raman scattering and x-ray photoelectron measurement, it is considered that the substitution site of Mn ions varies with an increase of doping amount x, which also leads to the change of valence state of Mn ions and the lattice structure, and further affects the strength of magnetic interaction and spin-lattice coupling. [ABSTRACT FROM AUTHOR]

SnO2:Cu memristor devices were fabricated to investigate the influence of Frenkel defects on endurance behavior. We controlled the oxygen pressure during pulsed laser deposition to obtain different Frenkel defect conditions. For SnO2:Cu devices with homogeneous Frenkel defects, high-resistance state (HRS) fatigue was observed with increasing switching cycles due to the reduction of interfacial barriers caused by unrecoverable fragments of conductive filaments. In bilayer SnO2:Cu devices with Frenkel defect concentration gradients, the vertical Fick force resulting from the concentration gradient can drive mobile oxygen ions to restrain the formation of unrecoverable fragments. Thus, HRS fatigue was improved by restraining the reduction of interfacial barriers. When the gradient becomes large, the bilayer devices demonstrate HRS rise and stuck switching in several switching cycles. In this case, the Fick force may dominate the diffusion of mobile oxygen ions, leading to the overfilling of oxygen vacancies at the interface and an increase in interfacial barriers. [ABSTRACT FROM AUTHOR]

The structural, electric, and magnetic properties were investigated in multisusceptible BaAlxFe12−xO19 (x = 0, 1, 2, and 3) ceramics. It is found that the magnetic domain structure changes abruptly with the increase in the Al3+ concentration, which is responsible for the abnormal coercivity enhancement and the distinct initial magnetization behavior. Smaller Al3+ doping increases the off-center displacement of Fe3+ ions at the trigonal bipyramid by introducing compressive strain, which thus enhances the stability of the ferroelectric phase and improves the ferroelectric Curie temperature of BaFe12O19. Moreover, more stable Al3+ ions can increase the resistance of BaFe12O19. The present results highlight the possible application of Al3+ doped BaFe12O19 ceramics as a multisusceptible single-phase material on multifunctional electronic devices. [ABSTRACT FROM AUTHOR]

III-N semiconductor resonant tunneling diodes (RTDs) have attracted great research interest because of their potential high speed performance. Thin film III-N RTDs are challenging due to high dislocation densities resulted from large lattice and thermal expansion coefficient mismatches to substrates. Here the authors present the growth and fabrication of AlN/GaN double barrier nanowire RTDs. The AlN/GaN double barrier nanowire RTDs show clear negative differential resistance with an onset voltage between 3.5 V and 4.5 V at both room and cryogenic temperatures. The bipolar tunneling and temperature dependent device performance suggest that the electron transport of these devices is based on resonant tunneling. [ABSTRACT FROM AUTHOR]