C.L. Chen

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.

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.

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.

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.

Ultraviolet photovoltaic effect in BiFeO3/Nb-SrTiO3 heterostructure

We report on ultraviolet photovoltaic effects in a BiFeO3/Nb-doped SrTiO3 heterostructure prepared by a pulsed laser deposition method. The heterostructure exhibits rectifying behaviors in the temperature range from 80 K to 300 K. The photovoltage of heterostructure is about 0.33 V at T = 80 K when it is illuminated by a KrF excimer laser with a wavelength of 248 nm. The peak photovoltages decrease with increasing the temperature because of the accumulation of photogenerated carriers. Moreover, the peak photovoltages of heterostructure almost linearly increase with an increase of the power density of laser at T = 300 K. The results reveal some properties that may be useful for possible applications in multiferroic photoelectric devices.

Photoinduced resistivity change of electron-doped La0.8Te0.2MnO3 film

In this paper, electron-doped La0.8Te0.2MnO3 film has been prepared on SrTiO3 (100) substrate by pulsed laser deposition method, and the photoinduced resistivity change and colossal magnetoresistance effect have been investigated. The results show that the film has a high metal-insulator transition temperature TMI of ∼283 K and the maximum magnetoresistance ratio is ∼24% at 0.7 T. Under laser irradiation, TMI varies from 283 to 243 K and resistivity increases below TMI, while it decreases above TMI. The maximum photoinduced resistivity change in resistivity (LR%) is 134.8%. The photoinduced relaxation character of the film indicates that the relaxation of photoinduced character relates to the excitation of small polarons.

Voltage-modulated negative and positive magnetoresistance in La0.7Sr0.3MnO3/Si heterostructure

Magnetotransport properties have been investigated in a La0.7Sr0.3MnO3/Si heterostructure, which exhibits good rectifying behaviour and voltage-modulated negative and positive magnetoresistance effects. The application of magnetic fields induces an increase in the current at a low bias voltage and a decrease at a high bias. This is caused by the effect of the voltage on the ferromagnetic state in the La0.7Sr0.3MnO3 film at the interface by the field-direction-dependent lattice distortion at a high bias voltage.

Favorable magnetoelectric phenomenon in Co2MnSi/PbTiO3 (001) ultrathin bilayer: A density functional theory study

Using density functional theory, magnetoelectric (ME) effect for [001]-oriented Co2MnSi/PbTiO3 ultrathin bilayer is demonstrated by changing interface configuration. Within paraelectric state, the interfacial stability is argued by phase diagram. With the reversal of electric polarization, the favorable change in local magnetization can be achieved for modified MnMn/TiO2 and CoCo/PbO interfaces. Electronic hybridization and spin-dependent charge screening are expected to be mainly responsible for the ME phenomena we address. The obtained results suggest that Co2MnSi/PbTiO3 (001) bilayer could be utilized in the area of electrically controlled magnetism, especially the bilayer with MnMn/TiO2 interface.

Phase-field modeling of growth pattern selections in three-dimensional channels

In this paper, the anisotropic crystal growth in three-dimensional channels was studied using a thin-interface phase-field model. Different growth modes and dynamics behaviours, including planar front, stationary symmetrical single finger, oscillatory symmetrical single finger and multiple-finger structure, have been observed as the undercooling is increased. Lower boundary of undercooling for symmetrical single finger results from the tip-widening while the upper boundary results from the tip-splitting instability. Results show that the existence range of the symmetrical single finger depends on crystalline anisotropy, channel size and dimensionality. Moreover, an oscillatory instability, involving tip velocity and tip radius oscillations, was evidenced when the undercooling is close to but below the upper boundary. We found that the oscillatory symmetrical single finger strongly depends on the channel size and the crystalline anisotropy. Mechanism of the oscillatory mode has been discussed in details.

Temperature dependent transport and photoresponse properties of a Mn-doped ZnO/p-Si heterojunction

A Mn-doped ZnO (ZMO) thin film was deposited on a p-Si (100) substrate by magnetron sputtering technology. The structure and morphology of the film were tested by x-ray diffraction and atomic force microscopy. The temperature dependent transport and photoresponse properties of the ZMO/Si heterojunction were also investigated. Results show that the ZMO film was successfully deposited in the polycrystalline structure with a smooth and crack-free surface. The current–voltage (I–V) curves show that the heterojunction exhibits excellent rectifying behavior. As temperature is decreased, the ideality factor of the heterojunction becomes remarkably large, implying a significant change of transport mechanism with differing temperatures. Photocurrent can emerge by illumination. Under reverse bias, the photocurrent increases drastically with the increase of reverse bias and then becomes saturated beyond a certain voltage. In addition, the critical voltage increases with the increase of temperature.