Hao Ni

Ferroelastic strain control of multiple nonvolatile resistance tuning in SrRuO3/PMN-PT(111) multiferroic heterostructures

The electric-field-tunable resistance switching in elastically coupled SrRuO3 thin films grown on (111)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 ferroelectric-crystal substrates has been investigated. During the ferroelectric poling process, the resistance evolution tracks the electric-field-induced in-plane strain of the film efficiently, revealing strain but not the electrostatic charge-mediated coupling mechanism. Using 109° and 71° ferroelastic domain switching of the substrate, multiple reversible and nonvolatile resistance states can be achieved at room temperature, which is closely related to the relative proportion of in-plane polarization vectors and induced distinct in-plane strain states after domain switching. Our findings provide an approach to elucidate electrically driven domain switching dynamics and design energy efficient, high-density spintronic memory devices.

Oxygen deficiency and cooling field driven vertical hysteretic shift in epitaxial SrRuO3/SrTiO3 heterostructures

SrRuO3 thin films have been epitaxially grown on SrTiO3 substrates using a pulsed laser deposition technique. By adjusting the oxygen partial pressure during deposition, a sharp drop in the Curie temperature ( T C) of 95 K and vertical magnetization shift ( M Shift) of 82.7% in the hysteresis loop was observed due to the oxygen deficiency induced lattice distortion that modifies the strong hybridization of p-d orbitals and perpendicular uniaxial magnetic anisotropy. In particular, the vertical hysteretic shift can also be effectively tuned by the applied cooling field, and thus, we obtained a giant and complete M Shift of 106% with a large volume of pinned Ru4+ moments. These findings reveal the critical role played by intrinsic oxygen defects and extrinsic cooling field in controlling magnetic couplings in this perovskite-type complex oxide system.

Large nonvolatile multiple-state resistive switching in TiO2−δ/PMN-PT field-effect device

TiO2−δ thin films were epitaxially grown on (001)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) ferroelectric single-crystal substrates. By applying electric fields E across the PMN-PT, the TiO2−δ film resistance could be reversibly switched into different stable states at room temperature. The on-off ratio, tuned by the strength of the electric field E, remained at ∼1 under the E ≤ 0.6 kV/cm and reached ∼3413 with the E increasing to 6 kV/cm, leading to a promising approach for designing nonvolatile multiple-state memory devices. By taking into account the migration of the oxygen vacancies and the ferroelectric field effect induced charge manipulations, the mechanism of the multiple-state resistive switching behaviors was discussed.

Optically and electrically co-controlled resistance switching in complex oxide heterostructures

The lattice degree of freedom has been utilized to pursue exotic functionalities in complex oxide heterostructures via various external stimuli, such as light, electric field, and magnetic field. Here, the epitaxial heterostructures composed of photostrictive SrRuO3 thin films and ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single-crystal substrates are fabricated to investigate the light and electric field co-control of lattice order in resistance switching. The electric-field-induced strain-mediated electroresistance response can be effectively tuned by light illumination. This, together with the electric-field-tunable photoresistance effect, demonstrates strong correlation between the light and the electric field, which is essentially mediated by strain-driven lattice-orbital coupling. Our findings provide a platform for realizing multi-field tuning of the lattice degree of freedom and the resultant functionalities in complex oxide heterostructures.

Ferroelastically and magnetically co-coupled resistive switching in Nd0.5Sr0.5MnO3/PMN-PT(011) multiferroic heterostructures

The phase separation, i.e., the competition between coexisting multi-phases, can be adjusted by external stimuli, such as magnetic field, electric field, current, light, and strain. Here, a multiferroic heterostructure composed of a charge-ordered Nd0.5Sr0.5MnO3 thin film and a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal is fabricated to investigate the lattice strain and magnetic field co-control of phase separation in resistive switching. The stable and nonvolatile resistance tuning is realized at room temperature using the electric-field-induced reversible ferroelastic strain effect, which can be enhanced by 84% under the magnetic field. Moreover, the magnetoresistance can be effectively tuned by the electrically driven ferroelastic strain. These findings reveal that the ferroelastic strain and the magnetic field strongly correlate with each other and are mediated by phase separation. Our work provides an approach to design strain-engineered multifunctional memory devices based on complex oxid...

Photoresponse in La0.9Hf0.1MnO3/0.05wt%Nb-doped SrTiO3 heteroepitaxial junctions

Excellent photo detectors need to have the rapid response and good repeatability from the requirement of industrial applications. In this paper, transport behavior and opto-response of heterostructures made with La0.9Hf0.1MnO3 and 0.05wt%Nb-doped SrTiO3 were investigated. The heterojunctions exhibited an excellent rectifying feature with very low leakage in a broad temperature region (from 40 to 300 K). These thin films presented persistent and stable photovoltages upon light illumination. Rapid shift between small and large voltages corresponding to “light OFF” and “light ON” states, respectively, was observed, demonstrating reliable photo detection behavior. A semiconductor laser with a wavelength of 650 nm was used as the light source. It is also noted that the observed photovoltages are strongly determined by light intensity. The injection of photoexcited charge carriers (electrons) could be responsible for the appearance of the observed opto-response. Such manipulative features by light irradiation e...

Oxygen defect influenced gas sensing properties of ZnO polyhedral structures

ZnO polyhedral structures were fabricated via a rapid thermal evaporation process. The ZnO nanostructures grown had faceted trumpet-like morphologies. The intensity of visible emission in photoluminescence spectra strongly related to growth temperature, indicating different concentrations of oxygen vacancy. These structures exhibited typical sensing property to gaseous ethanol. The sensing property was related to the oxygen vacancies.