Shengwei Yang

Non-volatile 180° magnetization reversal by an electric field in multiferroic heterostructures.

The deterministic rotation of magnetization by electric fields is a challenging issue for future low-power spintronics. In a Co/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 multiferroic heterostructure, piezostrain-mediated, macroscopically maneuverable, and non-volatile magnetization reversal without an applied magnetic field is demonstrated. This, combined with the presented phase-field simulations, is of practical relevance for designing prototype devices.

Coexistence of four resistance states and exchange bias in La0.6Sr0.4MnO3/BiFeO3/La0.6Sr0.4MnO3 multiferroic tunnel junction

The ferroelectric and tunnel electro- and magnetoresistance properties in La0.6Sr0.4MnO3/BiFeO3/La0.6Sr0.4MnO3 multiferroic tunnel junctions sandwiched with the antiferromagnetic-ferroelectric BiFeO3 as a tunnel barrier were reported. Besides the four non-volatile resistance states and the interfacial magnetoelectric coupling effect with the tunnel magnetoresistance manipulated by ferroelectric polarizations, one of the most important results is that the exchange bias effect on the tunnel magnetoresistance is observed in this junction due to the magnetic interaction between antiferromagnetic BiFeO3 and ferromagnetic La0.6Sr0.4MnO3 layers. These finds may be helpful for designing exchange bias based multiferroic tunnel junction in next generation random access memory devices.

Multi-state resistive switching memory with secure information storage in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure

The ferroelectric polarization dependent bipolar and conductive filament related unipolar resistive switching behaviors are investigated systematically in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure. The results show that after conductive filaments are formed, the ferroelectric state previously polarized will keep almost unchanged. By combining the two resistive switching mechanisms together under appropriate programming conditions, a tri-state-like resistive switching behavior is realized, finding effective routes in designing high-density storage. According to these distinctive characteristics, a prototype memory device with secure information storage is properly designed as an example of promising applications

Coaction and distinguishment of converse piezoelectric and field effects in La0.7Ca0.3MnO3/SrTiO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructures

The volatile and nonvolatile electroresistances related to the converse piezoelectric induced strain and ferroelectric field effects are improved in La0.7Ca0.3MnO3/SrTiO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructures by inserting a SrTiO3 buffer layer. Due to the coaction of the strain and field effects, the tri-resistance states are observed, and the relative contributions of the two effects on the resistance changes can be quantitatively distinguished by a programmable control of the polarization electric fields in “ON” and “OFF” modes, respectively. Our results indicate that the well-designed heterostructure exhibits potential for application in multifunctional devices.

Effects of Interface Layers and Domain Walls on the Ferroelectric-Resistive Switching Behavior of Au/BiFeO3/La0.6Sr0.4MnO3 Heterostructures

The electric field effects on the electric and magnetic properties in multiferroic heterostructures are important for not only understanding the mechanisms of certain novel physical phenomena occurring at heterointerfaces but also offering a route for promising spintronic applications. Using the Au/BiFeO3/La0.6Sr0.4MnO3 (Au/BFO/LSMO) multiferroic heterostructure as a model system, we investigated the ferroelectric-resistive switching (RS) behaviors of the heterostructure. Via the manipulation of the BFO ferroelectric polarizations, the nonvolatile tristate of RS is observed, which is closely related to the Au/BFO and BFO/LSMO interface layers and the highly conducting BFO domain walls (DWs). More interestingly, according to the magnetic field dependence of the RS behavior, the negative magnetoresistance effect of the third resistance state, corresponding to the abnormal current peak in current-pulse voltage hysteresis near the electric coercive field, is also observed at room temperature, which mainly arises from the possible oxygen vacancy accumulation and Fe ion valence variation in the DWs.

Tunable dielectric and ferroelectric properties in heteroepitaxial PbZr0.52Ti0.48O3/La0.625Ca0.375MnO3 thin films

In this work, the PbZr0.52Ti0.48O3/La0.625Ca0.375MnO3 (PZT/LCMO) thin films show a large magnetodielectric effect up to 52% at 3 MHz in a field of 0.8 T near the ferromagnetic Curie temperature Tc of LCMO. According to the equivalent RC-circuit fitting, the large magnetodielectric effect is found to be closely related to the interface behaviors between PZT and LCMO, which exhibits impressive magnetodielectric and magnetoresistance effects. Meanwhile, the extrinsic change of the ferroelectric coercive field Ec and remnant polarization Pr can be explained by the variations of voltage drop and space-charge related polarization. These findings improve our comprehension of magnetoelectric coupling in multiferroic heterostructure, and may provide potential application for multifunctional devices in spintronics.

Effects of magnetic electrode on the ferroelectric properties in heteroepitaxial BiFeO3/La0.625Ca0.375MnO3 thin films

The ferroelectric properties of the BiFeO3/La0.625Ca0.375MnO3 (BFO/LCMO) heterostructures were investigated using different bottom electrode configurations at different magnetic fields and temperatures. It is found that the apparent coercive voltage (Vac) increases linearly with the increase of LCMO resistances for different electrodes, and the extrinsic relative contribution from different LCMO electrodes to the variation of Vac caused by magnetic field can be quantitatively analyzed based on the scenario of voltage drop model. The magnetic field and temperature dependences of the heterostructure coercive voltage (Vac0) obtained by subtracting the voltage drop on LCMO from Vac are closely related to the interface behaviors. These findings not only further elucidate the physics of magnetoelectric coupling in multiferroic heterostructures but also are helpful for designing artificial prototype device.

Colossal anisotropic resistivity and oriented magnetic domains in strained La0.325Pr0.3Ca0.375MnO3 films

Magnetic and resistive anisotropies have been studied for the La0.325Pr0.3Ca0.375MnO3 films with different thicknesses grown on low symmetric (011)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. In the magnetic and electronic phase separation region, a colossal anisotropic resistivity (AR) of ∼105% and an anomalous large anisotropic magnetoresistance can be observed for 30 nm film. However, for 120 nm film, the maximum AR decreases significantly (∼2 × 103%) due to strain relaxation. The colossal AR is strongly associated with the oriented formation of magnetic domains, and the features of the strain effects are believed to be useful for the design of artificial materials and devices.

Multiferroic properties of neodymium and cobalt co-doped four-layer Aurivillius compounds

Single-phase multiferroic materials have attracted much attention in recent years due to their rich fundamental physics and great application potential^[1]. In the last few years, the bismuth-based Aurivillius phase compound, which is formed by stacking fluorite-like (Bi₂O₂)²⁺ layers and per-oskite-like (A_n-1B_nO_3n+1)^2-, is one of the most promising candidates of single-phase multiferroic materials by doping magnetic cations at B site^[2]. Recently, co-doped Aurivillius compounds have been reported to present an enhanced ferroelectric or ferromagnetic properties^[3].

Manipulation of morphologies and magnetic properties for Bi4.2K0.8Fe2O9+δ nanostructures

In this paper, Bi4.2K0.8Fe2O9+δ nanostructures with different morphologies, such as dispersible nanobelts, urchin-like and floriated micronanostructures with dendrites in different sizes, were controllably synthesized by a surfactant-free hydrothermal method. The temperatures of the KOH solutions in the co-precipitation step and the hydrothermal reactions had great effects on not only the morphologies but also the magnetic properties of the products. It was found that the low-temperature-fabricated urchin-like samples had a higher magnetization value. The special cores of the urchin-like nanostructures may play a critical role in the enhanced magnetizations and spin-glass dynamic behaviors. These results provide a simple way to manipulate the morphology of low-dimensional Bi4.2K0.8Fe2O9+δ nanostructures as well as their related magnetic properties.