Kexin Jin

Positive colossal magnetoresistance effect in ZnO∕La0.7Sr0.3MnO3 heterostructure

In this letter, an oxide heterostructure has been fabricated by successively growing La0.7Sr0.3MnO3 and ZnO layers on a LaAlO3 (100) substrate using pulsed laser deposition. The ZnO∕La0.7Sr0.3MnO3 heterostructure exhibits good rectifying behavior and a positive colossal magnetoresistance (MR) effect over a temperature range of 77–280K. The maximum MR values are determined to be about 53.9% at H=0.5T and 36.4% at H=0.3T. A possible explanation is given in terms of the effect of magnetic fields on the depletion layer and the capture carriers effect at the interface.

Photoresponsive character of double-doped La2∕3(Ca1∕3Sr2∕3)1∕3MnO3 film

The transient resistance change induced by modulated laser pulse has been observed in the double-doped perovskite La2∕3(Ca1∕3Sr2∕3)1∕3MnO3 thin film prepared by rf magnetron sputtering method. The time response character of photoinduced voltage signal is independent of the bias current, but its photoinduced relative change in resistance is nonlinearly dependent on the bias current. All the phenomena in the perovskite film is explained by the double exchange model and the small polaron theory. This is very important in the practical application of a colossal magnetoresistance photoelectric switch.

Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface

We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems.

Photoinduced effect in charge-ordering La0.5Ca0.5MnO3 film

Charge-ordered La0.5Ca0.5MnO3 film has been deposited on (100)-LaAlO3 substrate using rf magnetron sputtering method. X-ray diffraction analysis shows that the bulk has orthorhombic structure and the film has the better epitaxial character. The charge-ordering transition temperature is about 280 K by fitting the resistance-temperature curve using the variable-range hopping model. The decrease in the resistance of the film irradiated by the laser is caused by the delocalization effect of the correlated electron system. The photoinduced relaxation exhibits different processes when the laser is on and off, which can be attributed to thermal fluctuation.

Ultraviolet photovoltage characteristics in ZnO/La0.7Sr0.3MnO3 heterostructure

Ultraviolet photovoltage characteristics have been observed in a ZnO/La0.7Sr0.3MnO3 heterostructure, which exhibits reproducible rectifying characteristics. The peak photovoltage is about 0.704 V and the rise time is about 10 ns for the photovoltaic pulse at T = 78 K when the heterostructure is irradiated by a 248 nm laser pulse of 25 ns duration. The peak photovoltages and the full widths at half-maximum decrease with increasing temperature. These might be attributed to the change in the fractions of the ferromagnetic insulating phases in the depletion layer.

Degenerate seaweed to tilted dendrite transition and their growth dynamics in directional solidification of non-axially oriented crystals: a phase-field study.

We report the results of a phase-field study of degenerate seaweed to tilted dendrite transition and their growth dynamics during directional solidification of a binary alloy. Morphological selection maps in the planes of (G, Vp) and (ε4, Vp) show that lower pulling velocity, weaker anisotropic strength and higher thermal gradient can enhance the formation of the degenerate seaweed. The tip undercooling shows oscillations in seaweed growth, but it keeps at a constant value in dendritic growth. The M-S instability on the tips and the surface tension anisotropy of the solid-liquid interface are responsible for the formation of the degenerate seaweed. It is evidenced that the place where the interfacial instability occurs determines the morphological transition. The transient transition from degenerate seaweed to tilted dendrite shows that dendrites are dynamically preferred over seaweed. For the tilted dendritic arrays with a large tilted angle, primary spacing is investigated by comparing predicted results with the classical scaling power law, and the growth direction is found to be less sensitive to the pulling velocity and the primary spacing. Furthermore, the effect of the initial interface wavelength on the morphological transition is investigated to perform the history dependence of morphological selection.

Potential enhancement in magnetoelectric effect at Mn-rich Co2MnSi/BaTiO3 (001) interface

Magnetoelectric (ME) effect at Co2MnSi/BaTiO3 (001) interfaces is demonstrated by using the first-principle calculations. Within paraelectric state, the calculated phase diagram reveals that the modified MnMn/TiO2 (MM/TO) interface could be stabilized under Mn-rich and Co-rich condition. Compared with previous Fe/BaTiO3 (Duan C. G. et al., Phys. Rev. Lett., 97 (2006) 047201) and Fe3O4/BaTiO3 (Niranjan M. K. et al., Phys. Rev. B, 78 (2008) 104405) interfaces, more net change in interface magnetization can be achieved at MM/TO interface when electric polarization reverses. The results suggest a sizable interface ME effect may be attained at Mn-rich Co2MnSi/BaTiO3 (001) interface, hence potential application in the area of electrically controlled magnetism.

Switching behavior of oxygen-deficient La0.6Ca0.4MnO3−δ thin films

Photoinduced switching of resistance by several orders of magnitude is observed in oxygen-deficient La0.6Ca0.4MnO3−δ thin films deposited on Si substrates. The magnitude of the transient photoconductivity could attain 95.9% at room temperature under 532nm cw laser illumination at laser intensity of 142mW∕cm2. The switching has a fast photoresponse effect on a nanosecond time scale when irradiated by a 532nm laser pulse of 7ns duration. The photocurrent and photoresponse times depend on the laser intensity and the applied electric field. These results can be important for practical applications in the manganite-based optical devices.

Prediction of giant magnetoelectric effect in LaMnO3/BaTiO3/SrMnO3 superlattice: The role of n-type SrMnO3/LaMnO3 interface

We study the magnetoelectric coupling for the [001]-oriented (LaMnO3)2/(BaTiO3)5/(SrMnO3)2 superlattice, by means of the density functional theory. An interesting transition between ferromagnetic ordering and antiferromagnetic ordering is demonstrated by switching ferroelectric polarization in short-period superlattice structure. The predicted ferroelectrically induced magnetic reconstruction is less sensitive to the choice of Coulomb-correction U within GGA + U scheme. A possible explanation is given in terms of the favorable effect of n-type SrMnO3/LaMnO3 interface. Our results suggest that a sizable magnetoelectric effect may be achieved in the short-period LaMnO3/BaTiO3/SrMnO3 superlattice, hence promising application in electrically controlled magnetic data storage.

Photoinduced phase transition and relaxation in bare SrTiO3 single crystals

The photoinduced insulator-metal phase transition and relaxation characteristics have been investigated in bare SrTiO3 single crystals. The photoinduced relaxation time constant after the irradiation shows an increase with increasing temperatures. The SrTiO3 single crystal has a cutoff wavelength and an absorption edge of spectrum at about 385 nm, which agrees well with the band gap. The photocurrent responsivity is 1.36 × 10−5 A/W at 300 nm wavelength. The relative change in resistance is more than above six orders at room temperature, possessing potential applications in ultraviolet sensitive and detecting devices.