We report the low-temperature anomalous magnetic behavior of ferrimagnetic spinels cobalt orthotitanate (Co2TiO4), which exhibits magnetic compensation behavior across 31.74 K, and cobalt orthostannate (Co2SnO4) exhibiting two sequential magnetic transitions, namely (i) ferrimagnetic to paramagnetic transition with Néel temperature TN ∼ 41 K and reentrant spin-glass behavior with glass transition temperature TSG ∼ 39 K. The Arrott plot (H/M versus M2) criterion has been used to extricate the order of sequential magnetic transitions occurring below TN. Negative slopes of the Arrott plots below 32 K, metamagnetic-like character of the M-H isotherms, anomalies in the specific-heat (CP T−1 versus T) below 15 K, and a zero-crossover of isothermal magnetic-entropy-change (ΔS) signify the presence of pseudo first-order discontinuous magnetic phase transition in the low-temperature regime 5 K ≤ T ≤ 32 K. The dc- and ac-susceptibilities of both Co2TiO4 and Co2SnO4 are interpreted in terms of frozen-spin-clusters, which are responsible for very large magnitudes of the coercivity HC ∼ 20 kOe and bipolar-exchange bias HEB ∼ −20 kOe observed below 10 K.
Thin-film transistors (TFTs) with high electrical performances (mobility > 10 cm/V s, V < 1 V, SS < 1 V/decade, on/off ratio ≈ 10) obtained from the silicon- and oxide-based single-crystalline semiconductor materials require high processing temperature and hence are not suitable for flexible electronics. Amorphous oxide-based transparent electronic devices are attractive to meet emerging technological demands where crystalline oxide-/silicon-based architectures cannot provide a solution. Here, we tackle this problem by using a novel amorphous oxide semiconducting material-namely, indium tungsten oxide (IWO)-as the active channel in flexible TFTs (FTFTs). Post-annealing temperature as low as 270 °C for amorphous IWO thin films deposited by radio frequency sputtering at room temperature could result in smooth morphology ( R ≈ 0.42 nm), good adhesion, and high carrier density ( n ≈ 7.19 × 10 cm). Excellent TFT characteristics of flexible devices could be achieved with linear field effect mobility μ ≈ 25.86 cm/V s, subthreshold swing SS ≈ 0.30 V/decade, threshold voltage V ≈ -1.5 V, and on/off ratio I/ I ≈ 5.6 × 10 at 3 V and stable operation during bending of the FTFT. Additionally, IWO TFTs were implemented as synapses, the building block for neuromorphic computing. Paired-pulse facilitation up to 138% was observed and showed an exponential decay resembling chemical synapses. Utilizing this characteristic, a high-pass dynamic temporal filter was devised providing increased gain from 1.55 to 21 when frequency was raised from 22 to 62 Hz. The high performance and stability of flexible TFTs obtained with IWO films demonstrate their promise for low-voltage electronic applications.
Aluminum doped zinc oxide thin films have been prepared by sputtering under argon gas pressure of 0.15 Pa at different radio frequency (RF) power densities to optimize the conditions for application in both bottom emitting and transparent OLEDs.
A co-sputtering of dual InGaZnO and ZnO targets, abbreviated by ZnO co-sputtered IGZO, is used to fabricate a high performance indium gallium zinc oxide (IGZO) thin film transistor in this work. The ZnO co-sputtered IGZO thin film exhibits smooth (Rrms ~ 0.29 nm), featureless, and amorphous structure with high carrier density (n ~ 4.29 × 10 17 cm -3 ). The performance and stability of ZnO co-sputtered IGZO TFT has been investigated and compared with the counterparts fabricated by a single ZnO and a-IGZO target respectively. Highest linear field effect mobility of 16.1 cm 2 /Vs with an Ion/Ioff ratio of 1.04 × 10 7 , saturation drain current of 3.8 μA at 5V, and the lowest threshold voltage of 2.0 V with sub-threshold swing of 0.21V/dec have been obtained for the ZnO co-sputtered IGZO TFT. Furthermore, the ZnO co-sputtered IGZO TFT exhibited only a threshold voltage shift (∆Vth) of 2.75 V under negative biased illuminated stress conditions for 2500s, whereas the IGZO and ZnO based TFTs suffered from a huge threshold voltage shift (∆Vth > 6 V) under the same conditions. The obtained performance and stability of TFTs with ZnO co-sputtered IGZO film is very promising for low voltage displays applications.
We report an experimental investigation of the electronic structure and magnetic properties of bulk and nanosized MnCo 2 O 4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is (Co 2þ 1ÀyA Zn 2þ yA ) A [Mn 3þ Co 3þ ] B O 4+δ , whereas B-site dilution results in (Co 2þ ) A [Mn 3þ 1ÀxB Zn 2þ xB Co 3þ ] B O 4Àδ . The strength of exchange interaction J ij between the magnetic ions in a bulk spinel lattice decreases by 15% for A-site dilution relative to the undiluted compound; however, B-site dilution results in an enhancement in J ij by 17%. The frequency and temperature dependence of dynamic-susceptibility [χ ac (f , T)] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature T F 125:7 K (for x B ¼ 0:2) and 154.3 K (y A ¼ 0:1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent zν ¼ 6:17 and microscopic spin relaxation time τ o ¼ 4:4 Â 10 À15 s for x B ¼ 0:2 (for y A ¼ 0:1, zν ¼ 5:2 and τ o ¼ 5:4 Â 10 À13 s). The amplitude and peak position in χ ac (T) decreases with an increase in the DC bias field, which indicates that the spin-glass phase can survive in the presence of low fields forming a critical line with an exponent 2/3. This behavior is similar to the de Almeida-Thouless (AT-line) analysis in the T-H phase diagram which supports the existence of spin-glass like behavior below T F in these Zn diluted spinels.
The structural and dielectric properties of NiO substituted NaNbO3 ceramics are reported. The orthorhombic (Pmna) crystal structure of NaNbO3 transforms to a lower symmetry monoclinic phase (Pbma) after the dilute dispersion of NiO. X-ray photoelectron spectroscopy reveals pentavalent “Nb,” monovalent “Na,” and divalent “Ni” states along with the signatures of non-local screening effects. The antiferroelectric to paraelectric transition (TAFE) accompanied by a structural change from the orthorhombic to the tetragonal phase shifts by 55 °C toward the low-temperature side, whereas the morphotropic phase boundary (TO-M) moves toward a higher temperature by 28 °C for nominal substitutions (x≤0.10). The generalized Lyddane-Sachs-Teller expression (ε0−S′ε∞)=(ωlωt)2 and thermodynamic free energy models are employed to explain the anomalous behaviour of the temperature dependence of relative dielectric permittivity (εr(T)) across TAFE and TO-M. The frequency dependence of ac-conductivity σac(ω) follows the Jonscher power law (σac = σ(0) + Aωs), suggesting the dominance of the phonon-assisted hopping mechanism, whereas the frequency independent term (σ(0)) was explained by Funke's Jump-Relaxation Model.
Dual active channel IZO/IGZO thin film transistors as such and with ZnO interlayer are fabricated and characterized to investigate the impact of ultra-thin ZnO insertion on their performance and bias stability.
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