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Abstract SrTiO3 is a model of the perovskite-like compounds for structural transition which inducing the intriguing physical properties around the critical phase transition temperature TAFD (antiferrodistortive, abbrev. as AFD). Here we report that the electrical transport behavior is a new way to quantify Nb concentration for Nb-doped SrTiO3. The lattice parameter (c), phase transition temperature (TAFD), and the carrier concentration (n) of SrTiO3 may be manipulated by niobium doping. TAFD increases with increasing the niobium content in a rate of about 30 K per (wt%, i.e. niobium element’s weight verses total weight) niobium and n in a rate of about 2.5 $$\times$$ × 1020/cm3 per (wt%) niobium.

This paper reports the effects of substrate-induced strain on the high-quality La0.5-xDyxCa0.5-ySryMnO3 (0≤x≤0.2) (LDCSMO) films grown on (00l) SrTiO3 (STO) substrate. LDCSMO films were epitaxially grown on the STO substrate along [001] direction. The lattice parameter c of the film increases relatively with the thickness increasing, and the in-plane tensile strain was controlled by varying the film thickness. The Raman results at room temperature show that the in-plane Mn-O bond stretching and MnO6 distortion were suppressed by the in-plane tensile strain with the thickness of film decreasing. The magnetic results show that the CO-AFM insulating phase and the weak FM phase coexist at low temperature, and spin-glass effect was found in all films. The ferromagnetic order and insulating state were enhanced by tensile strain in thinner film. This abnormal enhancement of insulating state may be ascribed to the disordering state due to the stronger FM and AFM competition and the dominated “dead layer” in thinner film. The improved FM ordering is resulted from the increased double-exchange interaction for the MnO6 distortion suppressed by the in-plane tensile strain in thinner film. These results indicate spin-phonon coupling could be manipulated by controlling strain in manganese oxide films.

Epitaxial orthorhombic YMn0.9Ru0.1O3 films with different thickness have been grown on (001)-SrTiO3 substrates by pulsed laser deposition (PLD). The crystal structure is well investigated by X-ray Diffraction. It is found that the out-of-plane parameter c slowly increases with decreasing thickness of samples because of the tensile strain between the films and substrates along c axis. The lengths of in-plane Mn-O bonds expand with the enhancement of strains, which is proved by Raman scatting. The magnetic measurements reveal that there exist two magnetic transition temperatures TN1 and TN2. The TN1 is close to that of orthorhombic YMnO3 bulk. With decreasing thickness of the films, TN1 keeps almost constant because of the small stain along c-axis. TN2, however, obviously increases from 117 K to 134 K, which could be related to the expansion of in-plane Mn-O bonds. Results show that the magnetic transition temperature of YMn0.9Ru0.1O3 films can be sensitively manipulated by the strain of the films.

The compressive LaMnO3+δ thin films with thickness of ∼20 nm are grown on LaAlO3 (001) single crystal substrates under various oxygen environment. With decreasing oxygen pressure, the in-plane compressive strain is enhanced. It is found that the breathing mode (Q1) and the basal plane distortion mode (Q2) of MnO6 octahedron are suppressed, while the octahedral stretching mode (Q3) is promoted. The promoted Q3 switches the orbital order from x2-1/y2-1 to (x2-y2)+(z2-1) type. The ferromagnetic (FM) transition temperature Tc increases from 85 K to 105 K and the low-temperature magnetization increases greatly by 175%. The abnormal enhancement of magnetization with decreasing oxygen pressure is ascribed to the strain enlarged FM domains due to the decreased MnO6 distortion and the switched orbital ordering. This result is advantageous to explain the novel phenomena in LaMnO3-related systems.

An immediate quenching using liquid N2 is applied for synthesizing the 5d transition-metal oxides (Sr1-xCax)2IrO4 (0 ≤ x ≤ 0.15) single phase. X-ray diffraction together with Rietveld refinement shows that the lattice parameters along a and c directions and the bond angle of Ir-O2-Ir decrease with the increase of Ca content. X-ray Absorption Fine Spectroscopy measurements prove that the valence of Ir and the average Ir-O bond-length substantially remain unchanged with Ca content increasing in the phase. The effective magnetic moment μeff and Néel temperature TN decrease simultaneously with increased Ca content. Electrical resistivity shows complex temperature dependence behavior, which follows the three-dimensional variable range hopping behavior at low temperature, Arrhenius-type behavior at middle-temperature, and a weak electronic localization in quasi-two-dimensional at high temperature.

Diluted magnetic semiconductors (DMSs), with the Curie temperature at room temperature, are of technological and fundamental importance. Defect engineering has been an effective way to introduce magnetic moments in various non-magnetic systems. Here we show firstly, InN film directly grown on (0001)-oriented Al2O3 substrate with In deficiency is ferromagnetic with its Curie temperature as high as 297K. The undesirable large lattice mismatch between the film and substrate leads to a peculiar surface structure that the film separates into distinct In-rich and In-poor regions. Our first-principles calculations suggest the defect of In-vacancy is responsible for the magnetism. A local magnetic moment of 2.5μB is found, in agreement with experimental results. Our findings demonstrate that room-temperature ferromagnetism can also be induced in narrow band gap semiconductors through defect engineering, which remains largely unexplored so far.

We report on experimental investigations of the growth of Ge1-xSnx film with thickness above the critical thickness using Molecular Beam Epitaxy. A series of Ge1-xSnx films with various Sn compositions up to 14% are deposited on a Ge buffer layer for growth at low temperatures close to the melting point of Sn. Analysis of various measurements shows that the Ge1-xSnx film is defect free in the XTEM image and that Sn is distributed almost uniformly in the film for Sn compositions up to 9.3%. The Sn composition of the films is higher than the Sn composition that is theoretically predicted to cause the energy band of Ge to change from an indirect to a direct bandgap; thus, the present investigation provides a method for growing direct bandgap GeSn film, which is desired for use in applications involving optoelectronic devices.

The hole doping effect on the magnetic properties of multiferroic YMn1-xZnxO3 was studied through investigating the local microstructures. Polycrystalline YMn1-xZnxO3 samples with x ranging from 0 to 0.22 are synthesized by solid-state reaction method. The x-ray diffraction patterns reveal that YMn1-xZnxO3 samples with low Zn2+ doping concentration (x<0.1) maintain single phase which show hexagonal structure with space group of P63cm. The temperature dependence of magnetization presents that the magnetic moment at low temperature and the FM transition temperature increase with increasing the doping concentration of Zn2+. Meanwhile, ferromagnetism induced by Zn2+ doping is found to become stronger. EXAFS analysis reveals the in-plane Mn-OP bond length decreases while the out-of-plane Mn-OA bond length keeps almost constant. The weak FM order is ascribed to order-to-disorder effect resulting from the diluted exchange interaction among Mn3+ ions and double-exchange interaction between the mixed valence-state of Mn3+ and Mn4+ by hole doping of Zn2+. [ABSTRACT FROM AUTHOR]

An attempt is made to examine the exchange biasing effect and its angular dependence for GdFe/FeMn bilayers. It is concluded that similarity between the positive and negative exchange baising (EB) suggest that the same magnetization reversal mechanism in the exchange biased GdFe/FeMn bilayers.

An immediate quenching using liquid N2 is applied for synthesizing the 5d transitionmetal oxides (Sr1-xCax)2IrO4 (0 ≤ x ≤ 0.15) single phase. X-ray diffraction together with Rietveld refinement shows that the lattice parameters along a and c directions and the bond angle of Ir-O2-Ir decrease with the increase of Ca content. X-ray Absorption Fine Spectroscopy measurements prove that the valence of Ir and the average Ir-O bond-length substantially remain unchanged with Ca content increasing in the phase. The effective magnetic moment μeff and Néel temperature TN decrease simultaneously with increased Ca content. Electrical resistivity shows complex temperature dependence behavior, which follows the three-dimensional variable range hopping behavior at low temperature, Arrhenius-type behavior at middle-temperature, and a weak electronic localization in quasi-two-dimensional at high temperature. [ABSTRACT FROM AUTHOR]

In this paper, we reported an extremely large out-of-plane/in-plane anisotropic transport ( ~ 109) in double layer ruthenates. The mechanism that may be responsible for this phenomenon is also explored here. Distinct from previously well studied layered materials which show large out-of-plane/in-plane electronic anisotropy (103–106), the Ti-doped Ca3Ru2O7 single crystals not only form quasi-2D layered structure, but also show phase separation within the layers. We found that Ti doping in Ca3Ru2O7 induced electronic phase separation between the insulating phase and weak localized phase. The ratio of these two phases is very sensitive to the Ti concentration. At typical concentration, the weak localized phase may form a channel on the background of the insulating phase within the ab plane. However, the small volume of weak localized phase makes it less likely to overlap in different layers. This results in a much larger electronic anisotropy ratio than pristine compound Ca3Ru2O7. This new mechanism provides a route for further increase electronic anisotropy, which will remarkably reduce current leak and power consumption in electronic devices. [ABSTRACT FROM AUTHOR]

By using first-principle calculations, the electronic and magnetic properties of the Ru-deficient SrRu1−xO3 (x = 1/32) have been investigated. The obtained results indicate that nearest Ru and O ions of the vacancy move away from the Ru-vacancy, while the nearest Sr ions shift toward the vacancy. Interestingly, an antiferromagnetic spin cluster is formed in the vicinity of the Ru-deficient site. This, in turn, gives rise to reduced overall magnetic moment which better agrees with the experiment values for SrRuO3 reported in the literature. The adjustment of O ions surrounding the vacancy splits the near-vacancy Ru t2g orbitals, and the unoccupied ones appear above the Fermi level. The truncated effect at the vacancy, modified Ru-O covalent bonds, and Ru-O-Ru angles have jointly stabilized the antiferromagnetic spin cluster. [ABSTRACT FROM AUTHOR]

We report p-type conductivity in wurtzite indium nitride (InN) experimentally and theoretically. The as-deposited InN films are implanted with various doses of Zn ions. The Hall coefficient is positive for samples with doses of 2.5 ~ 10   ×   1014 ions cm−2 at low temperature and turns negative as the temperature increases. This notable sign change of the Hall coefficient confirms the existence of mobile holes in Zn-implanted InN. Moreover, first principle calculations indicate that Zn may be a more stable p-type dopant in InN than that of Mg and Ba because of its low ionization energy. [ABSTRACT FROM AUTHOR]

The quaternary topological insulator Bi2−xSbxTe3−ySey has exhibited pronounced topological surface states with an insulating bulk. While most transport studies of these compounds are focused on thin flakes peeled from bulk crystals, we carefully analyzed the magneto transport properties of bulk Bi1.5Sb0.5Te1.8Se1.2. We have observed weak anti-localization (WAL) and nonlinear Hall effects at low temperatures. Using a multi-channel model, we decomposed the total conductance into three conducting channels of the bulk, impurity band and surface states at various temperatures. The conductance of the surface states is almost constant in the whole temperature range, and contributes about 19.1% in the total conductance at 1.9 K. [ABSTRACT FROM AUTHOR]

Oxides-semiconductor junctions have attracted great attention and exhibited promising potential in integrated devices in which the passing current is controlled by applying voltage. It is found that an oxygen-deficient SrTiO3−δ/p-GaAs junction displays an obvious rectifying effect. The SrTiO3−δ thin film is in the anomalous in-plain compressive strain, as confirmed by structural characterization. Investigations on the current–voltage curve show that the current decreases with the increasing temperature at the reverse bias, which suggests that the rectifying behavior may be attributed to the strain-assisted tunneling mechanism. The effect of strain or film thickness on the transport property is also discussed. [ABSTRACT FROM AUTHOR]

The hole doping effect on the magnetic properties of multiferroic YMn1-xZnxO3 was studied through investigating the local microstructures. Polycrystalline YMn1-xZnxO3 samples with x ranging from 0 to 0.22 are synthesized by solid-state reaction method. The x-ray diffraction patterns reveal that YMn1-xZnxO3 samples with low Zn2+ doping concentration (x<0.1) maintain single phase which show hexagonal structure with space group of P63cm. The temperature dependence of magnetization presents that the magnetic moment at low temperature and the FM transition temperature increase with increasing the doping concentration of Zn2+. Meanwhile, ferromagnetism induced by Zn2+ doping is found to become stronger. EXAFS analysis reveals the in-plane Mn-OP bond length decreases while the out-of-plane Mn-OA bond length keeps almost constant. The weak FM order is ascribed to order-to-disorder effect resulting from the diluted exchange interaction among Mn3+ ions and double-exchange interaction between the mixed valence-state of Mn3+ and Mn4+ by hole doping of Zn2+. [ABSTRACT FROM AUTHOR]

An immediate quenching using liquid N2 is applied for synthesizing the 5d transitionmetal oxides (Sr1-xCax)2IrO4 (0 ≤ x ≤ 0.15) single phase. X-ray diffraction together with Rietveld refinement shows that the lattice parameters along a and c directions and the bond angle of Ir-O2-Ir decrease with the increase of Ca content. X-ray Absorption Fine Spectroscopy measurements prove that the valence of Ir and the average Ir-O bond-length substantially remain unchanged with Ca content increasing in the phase. The effective magnetic moment μeff and Néel temperature TN decrease simultaneously with increased Ca content. Electrical resistivity shows complex temperature dependence behavior, which follows the three-dimensional variable range hopping behavior at low temperature, Arrhenius-type behavior at middle-temperature, and a weak electronic localization in quasi-two-dimensional at high temperature. [ABSTRACT FROM AUTHOR]