arXiv subjects

G. Y. Wang

Publications and source records attributed to G. Y. Wang.

23 records · Page 2Linked to original sources

arXiv2004

Hysteresis and Anisotropic Magnetoresistance in Antiferromagnetic $Nd_{2-x}Ce_xCuO_{4}$

The out-of-plane resistivity ($ρ_c$) and magnetoresistivity (MR) are studied in antiferromangetic (AF) $Nd_{2-x}Ce_xCuO_{4}$ single crystals, which have three types of noncollinear antiferromangetic spin structures. The apparent signatures are observed in $ρ_c(T)$ measured at the zero-field and 14 T at the spin structure transitions, giving a definite evidence for the itinerant electrons directly coupled to the localized spins. One of striking feature is an anisotropy of the MR with a fourfold symmetry upon rotating the external field (B) within ab plane in the different phases, while twofold symmetry at spin reorientation transition temperatures. The intriguing thermal hysteresis in $ρ_c(T,B)$ and magnetic hysteresis in MR are observed at spin reorientation transition temperatures.

cond-mat.str-el↗

arXiv2004

Effect of oxygen content on the transport properties and magnetoresistance in [Ca$_{2}$CoO$_{3-δ}$]$_{0.62}$[CoO$_{2}$] single crystals

Transport property is investigated in [Ca$_{2}$CoO$_{3-δ}$]$_{0.62}$[CoO$_{2}$] single crystals obtained by varying annealing conditions. The $ρ_{ab}(T)$ exhibits a resistivity minimum, and the temperature corresponding to this minimum increases with the loss of oxygen content, indicative of the enhancement of spin density wave (SDW). Large negative magnetoresistance (MR) was observed in all single crystals [Ca$_{2}$CoO$_{3-δ}$]$_{0.62}$[CoO$_{2}$], while a magnetic-field-driven insulator-to-metal (IM) transition in oxygen annealed samples. These results suggest a ferromagnetic correlation in system enhanced by oxygen content. In addition, a low temperature thermal activation resistivity induced by fields was observed in single crystals annealed in oxygen atmosphere.

cond-mat.str-el↗

arXiv2004

Dimensional crossover and anomalous magnetoresistivity in single crystals $Na_xCoO_2$

The in-plane ($ρ_{ab}$) and c-axis ($ρ_c$) resistivities, and the magnetoresistivity of single crystals $Na_xCoO_2$ with x = 0.7, 0.5 and 0.3 were studied systematically. $ρ_{ab}(T)$ shows similar temperature dependence between $Na_{0.3}CoO_2$ and $Na_{0.7}CoO_2$, while $ρ_c(T)$ is quite different. A dimensional crossover from two to three occurs with decreasing Na concentration from 0.7 to 0.3. The angular dependence of in-plane magnetoresistivity for 0.5 sample shows a \emph{"d-wave-like"} symmetry at 2K, while the \emph{"p-wave-like"} symmetry at 20 K. These results give an evidence for existence of a \emph{spin ordering orientation} below 20 K turned by external field, like the stripes in cuprates.

cond-mat.str-el↗

arXiv2004

Magnetic and Transport Properties in $CoSr_2Y_{1-x}Ca_xCu_2O_7$ ($x$=0$\sim$0.4)

Magnetic and transport properties of $Co Sr_2 Y_{1-x} Ca_x Cu_2 O_7$ ($x=0 \sim 0.4$) system have been investigated. A broad maximum in M(T) curve, indicative of low-dimensional antiferromagnetic ordering originated from $CoO_{1+δ}$ layers, is observed in Ca-free sample. With increasing Ca doping level up to 0.2, the M(T) curve remains almost unchanged, while resistivity is reduced by three orders. Higher Ca doping level leads to a drastic change of magnetic properties. In comparison with the samples with $x=0.0 \sim 0.2$, the temperature corresponding to the maximum of M(T) is much lowered for the sample $x$=0.3. The sample $x$=0.4 shows a small kink instead of a broad maximum and a weak ferromagnetic feature. The electrical transport behavior is found to be closely related to magnetic properties for the sample $x$=0.2, 0.25, 0.3, 0.4. It suggests that $CoO_{1+δ}$ layers are involved in charge transport in addition to conducting $CuO_2$ planes to interpret the correlation between magnetism and charge transport. X-ray photoelectron spectroscopy studies give an additional evidence of the the transfer of the holes into the $CoO_{1+δ}$ charge reservoir.

cond-mat.str-el↗

arXiv2004

Raman spectra in epitaxial thin films $La_{1-x}Ca_xMnO_3$ (x = 0.33, 0.5) grown on different substrates

Raman spectra of LCMO films grown on LAO (001), STO (001), and MgO (001) substrates were studied at different temperatures. The effect of temperature, doping level and strain on Raman spectra are discussed in detail. With decreasing temperature, the changes of Raman spectra are correlated with the disorder-order transition, shuch as: paramagnetism to ferromagnetism, and charge-ordering. The strain induced by lattice-substrate mismatch affects the Raman spectra strongly. The mode induced by disorder of oxygen defects is apparently observed in $La_{0.67}Ca_{0.33}MnO_3$ film on STO due to the larger tensile strain. While this mode can not be seen in the Raman spectra for the films on LAO and MgO. A strong unsigned mode at about 690 $cm^{-1}$ is observed in all films except for $La_{0.67}Ca_{0.33}MnO_3$ film on LAO, which is not observed in bulk sample easily. It suggests that the mode is closely related to the strain.

cond-mat.str-el↗