Feng-Xian Jiang

Robust Interfacial Exchange Bias and Metal-Insulator Transition Influenced by the LaNiO3 Layer Thickness in La0.7Sr0.3MnO3/LaNiO3 Superlattices

Artificial heterostructures based on LaNiO3 (LNO) have been widely investigated with the aim to realize the insulating antiferromagnetic state of LNO. In this work, we grew [(La0.7Sr0.3MnO3)5-(LaNiO3)n]12 superlattices on (001)-oriented SrTiO3 substrates by pulsed laser deposition and observed an unexpected exchange bias effect in field-cooled hysteresis loops. Through X-ray absorption spectroscopy and magnetic circular dichroism experiments, we found that the charge transfer at the interfacial Mn and Ni ions can induce a localized magnetic moment. A remarkable increase of exchange bias field and a transition from metal to insulator were simultaneously observed upon decreasing the thickness of the LNO layer, indicating the antiferromagnetic insulator state in 2 unit cells LNO ultrathin layers. The robust exchange bias of 745 Oe in the superlattice is caused by an interfacial localized magnetic moment and an antiferromagnetic state in the ultrathin LNO layer, pinning the ferromagnetic La0.7Sr0.3MnO3 layers together. Our results demonstrate that artificial interface engineering is a useful method to realize novel magnetic and transport properties.

Interfacial Spin Glass State and Exchange Bias in the Epitaxial La0.7Sr0.3MnO3/LaNiO3 Bilayer

We study the magnetic properties of an epitaxial growth bilayer composed of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and paramagnetic LaNiO3 (LNO) on SrTiO3 (STO) substrates. We find that the stack order of the bilayer heterostructure plays a key role in the interfacial coupling strength, and the coupling at the LSMO(top)/LNO(bottom) interface is much stronger than that at the LNO(top)/LSMO(bottom). Moreover, a strong spin glass state has been observed at the LSMO/LNO interface, which is further confirmed by two facts: first, that the dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line and, second, that the relaxation of the thermal remnant magnetization can be fitted by a stretched exponential function. Interestingly, we also find an exchange bias effect at the LSMO/LNO bilayer below the spin glass freezing temperature, indicating that the exchange bias is strongly correlated with the spin glass state at its interface.

Morphology and magnetic properties of Fe3O4 nanodot arrays using template-assisted epitaxial growth

Arrays of epitaxial Fe3O4 nanodots were prepared using laser molecular beam epitaxy (LMBE), with the aid of ultrathin porous anodized aluminum templates. An Fe3O4 film was also prepared using LMBE. Atomic force microscopy and scanning electron microscopy images showed that the Fe3O4 nanodots existed over large areas of well-ordered hexagonal arrays with dot diameters (D) of 40, 70, and 140 nm; height of approximately 20 nm; and inter-dot distances (Dint) of 67, 110, and 160 nm. The calculated nanodot density was as high as 0.18 Tb in.−2 when Du2009=u200940 nm. X-ray diffraction patterns indicated that the as-grown Fe3O4 nanodots and the film had good textures of (004) orientation. Both the film and the nanodot arrays exhibited magnetic anisotropy; the anisotropy of the nanoarray weakened with decreasing dot size. The Verwey transition temperature of the film and nanodot arrays with Du2009≥u200970 nm was observed at around 120 K, similar to that of the Fe3O4 bulk; however, no clear transition was observed from the small nanodot array with Du2009=u200940 nm. Results showed that magnetic properties could be tailored through the morphology of nanodots. Therefore, Fe3O4 nanodot arrays may be applied in high-density magnetic storage and spintronic devices.

Contrasting behavior of the structural and magnetic properties in Mn- and Fe-doped In2O3 films

We have observed room temperature ferromagnetism in In2O3 thin films doped with either 5 at.% Mn or Fe, prepared by pulsed laser deposition at substrate temperatures ranging from 300 to 600u2009°C. The dependence of saturation magnetization on grain size was investigated for both types of In2O3 films. It is revealed that, for the Mn-doped films, the magnetization was largest with small grains, indicating the importance of grain boundaries. In contrast, for Fe-doped films, the largest magnetization was observed with large grains.

The dramatic enhancement of ferromagnetism and band gap in Fe-doped In 2 O 3 nanodot arrays

Ordered Fe-doped In2O3 nanodot arrays with diameters between 35u2009nm and 80u2009nm are fabricated using pulsed laser deposition with the aid of ultrathin porous anodized aluminumoxide templates. The 5u2009at.% Fe doped In2O3 nanodot arrays are shown to consist of the cubic bixbyite structure of In2O3. The nanodot arrays are demonstrated to be doped by Fe ions with mixed valences ofu2009+2 andu2009+3, ruling out the presence of cluster and secondary phase related to Fe. The nanodot arrays exhibit the ferromagnetism at room temperature, where the magnetic moment increases as the dot size is reduced, rising to a maximum of about 230u2009emu/cm3 (equivalent to an average moment on the Fe ions of 15.30 µB/Fe). This indicates an effect due to the surface of the nanodot arrays. The optical band width is also increased to 4.55u2009eV for the smallest dot array, thus indicating that the surface states are responsible for the magnetism and also enhance the band gap due to Burstein-Moss effect. Our results will be benefit for understanding the physical properties of oxide semiconductor nanostructures in the application of nano-spintronics devices.

Room temperature ferromagnetism in metallic Ti1−xVxO2 thin films

Transition metal doped TiO2 diluted magnetic semiconductors have attracted considerable interest due to their room temperature ferromagnetism. However, most TiO2 films are highly insulating, and thus the magnetic properties can not be controlled by tuning the carrier concentration. This will limit their application in controlling magnetization via electrical gating. Here, we deposit rutile Ti1−xVxO2 (x = 0.03 and 0.05) films with the thickness between 30 and 245 nm by the pulsed laser deposition technique, and observe an obvious room temperature ferromagnetic behavior in all films. The high resolution X-ray photoelectron spectroscopy results indicate that V substituting Ti4+ ions in the TiO2 lattice, with the +3 valence state having two unpaired d electrons, is responsible for the local spin. More importantly, the systemic investigations of transport properties for Ti1−xVxO2 films reveal that the films are n-type and have metallic conductivity with a carrier density of about 1020/cm3. Further studies suggest that the oxygen vacancies play a dual role of contributing to the metallic conductivity of the Ti1−xVxO2 films, and also providing the free electrons to mediate the long-range ferromagnetic coupling between two magnetic polarons. These findings may offer promise for gate-tunable ferromagnetism in future semiconductor spintronics.

Observation of Superconductivity in the LaNiO3/La0.7Sr0.3MnO3 Superlattice

School of Chemistry and Materials Science, Key Laboratory of Magnetic Molecules and Magnetic Information Materials, Ministry of Education, Shanxi Normal University, Linfen 041004, China Atomic scale control of the hetero-interfaces in transition metal oxides has attracted significant attention due to the possibility of observing novel phenomena1,2. The cuprate- and ferrite-based interfacial superconductors have been investigated extensively, while the research of nickelate-based heterostructure is quite rare3,4. Recently Chaloupka and Khaliullin theoretically predicted that antiferromagnetism and high temperature superconductivity (SC) may be stabilized in LNO-based superlattices5. However, the superconductivity state in LNO-based heterostructure has not yet been experimentally reported. In this work, we investigate the properties of a superlattice (SL) composed of an ultrathin LaNiO3 layer, with a ferromagnetic insulating La0.7Sr0.3MnO3 LSMO) layer. Zero resistance and Meissner effect are observed by resistive and magnetic measurements on the superlattice, which gives experimental indication of superconductivity in new kinds of superconductors. X-ray linear dichroism causes the NiO2 planes to develop electron occupied

Enhancement of the metal-insulator transition temperature in La0.7Ca0.3MnO3 film by magnetic nanodots

x^{2}-y^{2}

Carrier-mediated nonlocal ferromagnetic coupling between local magnetic polarons in Fe-doped In2O3 and Co-doped ZnO

orbital order similar to a cuprate-based superconductor. Our findings demonstrate that artificial interface engineering is a useful way to realize novel physical phenomena, such as superconductivity. Typical x-ray diffraction scans through (002) symmetric reflections of the LNO/LSMO superlattice are shown in Fig. 1a. The main peak of the superlattice and satellite peaks of SL-1 and SL +1 are observed, suggesting sharp interfaces in this superlattice. The coherent epitaxial growth and the absence of secondary phases or dislocations in LNO/LSMO superlattice are both confirmed by high resolution high-angle annular dark field scanning transmission electron microscopy, as shown in Fig. 1b. Because the A site is similar to the superlattice, and the atomic number of B site is contrasted in this image, the LNO layers appear brighter than the LSMO layers The high quality epitaxial [(LNO)2/(LSMO)3]20 superlattice was measured with a current of 5E10-3 mA in a Van der Pauw geometry. In order to directly observe the superconducting property at low temperatures, the temperature dependence of resistivity was measured, as shown in the inset of Fig. 2a. The superlattice displays metallic behavior with the temperature below 10 K and the resistivity abruptly drops around 3.7 K, clearly indicating superconductivity. To further verify the superlattice nature of the observed superconductivity, we measure the magnetic susceptibility (χ) as a function of temperature at magnetic field (H) strength of 10 Oe. As shown in Fig. 2b, the zero field cooled (ZFC) and field cooled (FC) susceptibility are essentially temperature independent at low temperatures. A sharp drop of magnetic susceptibility is observed for both ZFC and FC processes, indicating that the magnetic onset of superconductivity appears around 3.5 K, which is the same as the zero-resistivity temperature. Further confirmation of superconductivity in the superlattice is shown in the inset of Fig. 2b, displaying the typical magnetic hysteresis curve for a superconductor at 2 K after zero-field cooled process. The characteristic M-H loop indicates that the present superlattice is a superconductor of the second kind with a lower critical field of 50 Oe. The work was supported by National Key R&D Program of China (No. 2017YFB0405703), NSFC (Nos. 61434002, 51571136, 11274214), and the Special Funds of Sanjin Scholars Program.

Effects of oxygen vacancy and local spin on the ferromagnetic properties of Ni-doped In2O3 powders

The magnetic and transport properties of a single layer of La0.7Ca0.3MnO3 are compared with one topped with magnetic nanodots formed from oxides of iron. Remarkably enhanced magnetization and metal-insulator transition temperature were observed for the decorated film capped with In2O3. The saturation magnetization increased by ∼35%, and the metal-insulator transition temperature increased from 75u2009K to 145u2009K at zero field. However, no enhancement was observed for either the La0.7Ca0.3MnO3 film with uncapped magnetic dots or the bilayer formed from La0.7Ca0.3MnO3 and In2O3.