Effect of Ga doping on charge transport mechanism of La0.85Zr0.15Mn1−xGaxO3

[[abstract]]Structural properties, temperature-dependent resistivity ρ(T) and thermoelectric power S(T) of La0.85Zr0.15Mn1−xGaxO3 (LZMGO) manganites with 0.0 ≤ x ≤ 0.06 have been extensively investigated. It is found that the Mn–O–Mn bond angle decreases and the Mn–O bond length increases with increasing Ga content, indicative of a significant distortion of MnO6 octahedra in LZMGO. The local lattice distortion and suppression of double exchange ferromagnetism induced by the Ga doping shift both Curie temperature (TC) and metal-insulator transition temperature (TMI) toward lower temperatures. Followed by the metal-insulator transition, ρ(T) exhibits an insulatinglike behavior accompanied by a relatively small value of S(T) below T∗ at low temperatures. An anomalous peak observed in S(T) is attributed to an enhancement of electron-magnon interaction caused by the Ga doping and a decrease in magnetic entropy near TMI. Three different charge transport mechanisms were identified in three temperature regions based on detailed analyses of ρ(T) and S(T) data. The small-polaron hopping mechanism governs the charge transport in the high-temperature paramagnetic region (T＞TMI). The polaron binding energy determined from the ρ(T) and S(T) data increases with increasing Ga content, suggesting that polaron in La0.85Zr0.15MnO3 has a magnetic nature. In addition, the electron-magnon scattering dominates the charge transport in the intermediate-temperature metallic region (T∗＜T＜TMI), whereas the transport behavior in the low-temperature insulating region (T＜T∗) can be described by the three-dimensional variable-range-hopping model.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙

Effect of Cr deficiency on physical properties of triangular-lattice antiferromagnets CuCr1−xO2 (0 ≦ x ≦ 0.10)

[[abstract]]Structural, transport, and magnetoelectric (ME) properties of delafossite oxides CuCr1-xO2 with 0 <= x <= 0.10 were extensively investigated. The Rietveld refinement shows that the Cu-O bond length decreases with increasing Cr deficiency, indicative of the presence of a mixed valence state of Cu+/Cu2+ and an enhancement of the hybridization between Cu 3d and O 2p orbitals. As a result, it leads to a decrease of room-temperature resistivity by two orders of magnitude. The deduced effective moment for the Cr-deficient samples is larger than the one only taking into account the contribution from Cr3+ with S = 3/2. This demonstrates that Cu2+ is present in the Cr-deficient samples, giving rise to excess holes at the Cu site. Below TN(Cr) ∼ 24 K, the magnetocapacitance [[variant_greek_epsilon](H)-[variant_greek_epsilon](0)]/[variant_greek_epsilon](0) exhibits a distinct field dependence and deviates from the square of magnetization M2. These findings suggest that the ME coupling in CuCr1-xO2 with higher x is modulated by an increase of the spin fluctuations in the CrO2 triangular lattice through the interplay between charge and spin degrees of freedom.[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子

Electronic structure of RuSr2EuCu2O8 studied by x-ray absorption and photoemission spectroscopies

[[abstract]]Local electronic structures of ruthenocuprate RuSr2EuCu2O8 (RuEu-1212) were investigated by using x-ray absorption near-edge structure (XANES) and valence-band photoemission (VB-PES) measurements at room temperature, 80 K, and 25 K. The XANES results indicate that when RuEu-1212 is below Curie temperature, TM, electrons are transferred not only from Cu 3d states, but also from Ru 4 d states, to O 2p orbitals. Additionally, the partial spectral weight distributions derived from VB-PES measurements provide evidence of a weak overlapping between Ru 4 d states and strongly Cu 3d−O 2p hybridized states below the Fermi level, which results in a weak coupling between the CuO2 and RuO2 layers. The analysis of extended x-ray absorption fine structure shows that the appearance of weak ferromagnetism and superconductivity is accompanied by a significant decrease of dynamic local lattice distortions of high-shell Cu-Sr and Ru-Sr bonding in RuEu-1212.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙

The electronic and magnetic properties of La0.85Zr0.15MnO3 deposited on SrTiO3 and MgO substrates

[[abstract]]The electronic and magnetic properties of tetravalent-ion-doped La0.85Zr0.15MnO3 (LZMO) thin films that were epitaxially grown on SrTiO3 (STO) and MgO substrates were studied using temperature-dependent x-ray diffraction (XRD), x-ray absorption near-edge structure, x-ray linear dichroism, and x-ray magnetic circular dichroism at the Mn L 3,2- and K-edge. XRD studies reveal that the LZMO thin films have compressive and tensile strains (along the c -axis) on the STO and MgO substrates, respectively. As the temperature is reduced from room temperature to below magnetic transition temperature, the preferentially occupied Mn majority-spin e g orbital changes from the in-plane dx 2 -y 2 to the out-of-plane d 3 z 2 -r 2 orbital for LZMO/STO, and vice versa for LZMO/MgO. Experimental results suggest that the new hopping path that is mediated by the Mn2+ ions triggers a stronger d 3 z 2 -r 2 orbital ordering of Mn3+ ions and enhances the ferromagnetic coupling between the Mn spin moments of t 2g electrons in LZMO/STO, whereas the strong tensile strain stabilizes the dx 2 -y 2 orbital by inducing lattice distortions of the MnO6 octahedra in LZMO/MgO.[[notice]]補正完畢[[incitationindex]]SCI[[cooperationtype]]國

Evidence for Intrinsic Josephson Junctions in a Single Crystal of YBa2Cu3O7-δ

[[abstract]]In the resistive transition just below Tc, the c-axis dynamic resistance of a YBa2Cu3O7-δ single crystal as a function of the external dc magnetic field applied parallel to the ab-plane shows peaks suggestive of the existence of Josephson junctions within the single crystal. Two types of Josephson junctions can be inferred: one group formed by the CuO2-Y-CuO2 triple atomic planes within the same unit cell and the other by the bilayers of CuO2 planes from different unit cells. Secondly, the microwave-induced dc voltages across an unbiased single crystal exhibit behaviors that are consistent with the inverse ac Josephson effect, further indicating the existence of Josephson junctions within the single crystal.[[journaltype]]國內[[booktype]]紙本[[countrycodes]]TW