Xingkun Ning

Enhanced polarization and dielectricity in BaTiO3:NiO nanocomposite films modulated by the microstructure

Parallel and vertical interfaces in vertically and parallelly aligned nanocomposite thin films have been shown to be an effective method to manipulate functionalities. However, tuning the physical properties by modulating the microstructure of the self-assembled nanocomposite films and understanding the physical properties underlying the manipulation is still a challenge. In this work, BaTiO3:NiO (BTO:NiO) nanocomposite films with nanomultilayer, nanocolumnar and nanogranular structures have been prepared on Nb:SrTiO3 (Nb:STO) substrates by a pulsed laser deposition (PLD) method. These films have been used as a model system to investigate the relationship between the microstructure and the ferroelectric properties. The polarization, dielectricity and leakage can be separately modulated by tuning the microstructures. The experimental results show that the remanent polarization of the nanocomposite films is much higher than that of the pure BTO films. By precisely modulating the microstructure, a significantly enhanced polarization (>70% higher than pure BTO for the nanomultilayer structure) and dielectricity (>60% and >240% higher than pure BTO for the nanomultilayer and nanocolumnar structure, respectively) are realized in these films. These results demonstrate that tunable ferroelectric properties can be realized by controlling the microstructures in the epitaxial BTO:NiO nanocomposite thin films, which will be expected to be applied in the devices such as supercapacitors, solar cells and non-volatile memory applications.

Polarization and charge-transfer effect on the transport properties in two-dimensional electron gases/LaNiO3 heterostructure

The film thickness dependent transport properties of the LaNiO3 (LNO) layer epitaxially grown on LaAlO3/SrTiO3 (LAO) 2-dimensional electronic gas (2DEG) have been investigated. The ultrathin LNO films grown on the 2DEG have a sheet resistance below the values of h/e2 in all temperature ranges. The electron density is enhanced by more than one order of magnitude by capping LNO films. X-ray photoelectron spectroscopy shows that the interface undergoes unambiguous charge transfer and electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. The polar-catastrophe of the 2DEG is directly linked to the electronic structure and transport properties of the LNO. The transport properties can be well modulated by the thickness of the LAO in the 2DEG, and the data can be well fitted with the polar-catastrophe scenario. These results suggest a general approach to tunable functional films in oxide heterostructures with the 2DEG.

The role of pd hybridization in the metal-insulator transition in NdNiO3 heterostructure

ABSTRACT Understanding and controlling phase transition in the transition-metal oxides is interesting from the fundamental physics point of view. The pd hybridization are of considerable issue to tune the phase transition temperature. Here, the transport properties of the NdNiO3 with artificial ultra-thin NiO insert layer have been investigated. The relationship between the essential parameters of the pd hybridization (T) and the metal-insulator transition (MIT) temperature has been clearly elucidated a monotone decreasing relationship. This work realized the combination of the engineering hybridization and the phase transition temperature, which might be significant for the development of multifunctional materials in the transition-metal oxides. GRAPHICAL ABSTRACT IMPACT STATEMENT The pd hybridization are of considerable issue to tune the phase transition temperature. Here, the pd hybridization have been tuned and elucidated a monotone decreasing relationship with the metal–insulator transition temperature.

Room temperature magnetoresistance properties in self-assembled epitaxial La0.7Sr0.3MnO3:NiO nanocomposite thin films

ABSTRACT Self-assembled epitaxial La0.7Sr0.3MnO3:NiO (LSMO:NiO) nanocomposite thin films were grown on (001)-oriented SrTiO3 substrates by pulsed laser deposition, and their microstructures and magnetoresistance (MR) properties were investigated. The room temperature MR effect at a low magnetic field has been realized in the composite films, and the maximum MR value is 18.7% at 300 K and 1 T. The room temperature MR properties at the low magnetic field can be attributed to the special structure, which is made up of the nano-sized LSMO and NiO columns. The room temperature MR properties at low magnetic fields will facilitate its extensive room temperature applications. GRAPHICAL ABSTRACT IMPACT STATEMENT The room temperature magnetoresistance properties at a low magnetic field has been realized in the self-assembled epitaxial La0.7Sr0.3MnO3:NiO nanocomposite thin films by controlling the microstructures.

Charge transfer effect at the La 0.7 Ca 0.3 MnO 3 /NiO heterojunction and the novel interface ferromagnetism

We report the formation of a new ferromagnetic (FM) states in the antiferromagnet (AFM) NiO at the interface with ferromagnet (FM) La_0.7Ca_0.3MnO₃ (LCMO). The new magnetization temperature at 80 K is observed and can be ascribed to Ni³⁺-O-Mn³⁺ superexchange interactions. Mn 3s and Ni 3p core-level spectra have been measured by x-ray photoelectron spectroscopy (XPS) which show a direct evidence of charge transfer effects of the type Mn⁴⁺-Ni²⁺ → Mn³⁺-Ni³⁺ at the interface region. The valence band offset (VBO) at the LCMO/NiO interface can be determined to be ΔE_VBO ~ 0.77 eV. The valence band of NiO is shifted to higher binding energy compared to LCMO. Thus, charge transfer occurred owing to the valence band edge shifting at the heterostructure interfaces.

Control of the ferromagnetic to paramagnetic transition in SrRuO 3 epitaxial films by electric field

The external electric field controlled the phase transition behavior for ferromagnetic thin films is important to realize its practical applications as spintronic devices. In this work, we report the electric field controlled ferromagnetic (FM) to paramagnetic (PM) transition in a SrRuO3/Pb(Mg1/3Nb2/3)O3-PbTiO3 (SRO/PMN-PT) heterostructures by adding a bias voltage. The FM to PM transition and the magnetoresistance (MR) have been dynamic controlled by the electric field. The Curie temperature (Tc) is changed from 154 K to 162 K as a result of external electric field applied to the PMN-PT substrates. It is demonstrated that the SRO film is closely associated with the strain states, which can be directly controlled by the bias voltage. Our finding offer novel opportunities for modulating phase transitions in a reversible non-volatile way.