Influence of sintering temperature on resistivity, magnetoresistance and thermopower of La0.67Ca0.33MnO3

Colossal Magnetoresistance Study in Nanophasic La_0.7Ca_0.3MnO_3 Manganite

In this study we report the effect of sintering temperature on the low field magnetotransport properties of La_0.7Ca_0.3Mn_O3 manganite synthesized through polymeric precursor route. The La_0.7Ca_0.3MnO_3 has been sintered at 600^oC (S6), 700^oC (S7), 800^oC (S8), 900^oC (S9) and 1000^oC (S10). XRD confirms that phase formation starts at 600^oC. All the samples are single phasic having orthorhombic unit cell. The lattice parameters decrease on lowering the sintering temperature (T_S). The crystallite as well as particle size also show strong dependence on the sintering temperature. All the sam…

Large linear magnetoresistance and magnetothermopower in layered SrZnSb$_2$

We report the large linear magnetoresistance ($\sim 300\%$ in 9 T field at 2 K) and magnetothermopower in layered SrZnSb$_2$ crystal with quasi-two-dimensional Sb layers. A crossover from the semiclassical parabolic field dependent magnetoresistance to linear field dependent magnetoresistance with increasing magnetic field is observed. The magnetoresistance behavior can be described very well by combining the semiclassical cyclotron contribution and the quantum limit magnetoresistance. Magnetic field also enhances the thermopower. Our results can be well understood by the magnetotransport of D…

Large enhancement of the thermopower in Na$_x$CoO$_2$ at high Na doping

Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate $\rm Na_xCoO_2$ displays several interesting electronic phases as $x$ is varied including water-induced superconductivity and an insulating state that is destroyed by field. Initial measurements showed that, in the as-grown composition, $\rm Na_xCoO_2$ displays moderately large thermopower $S$ …

Magnetic anisotropy, first-order-like metamagnetic transitions and large negative magnetoresistance in the single crystal of Gd$_{2}$PdSi$_3$

Electrical resistivity ($ρ$), magnetoresistance (MR), magnetization, thermopower and Hall effect measurements on the single crystal Gd$_{2}$PdSi$_3$, crystallizing in an AlB$_2$-derived hexagonal structure are reported. The well-defined minimum in $ρ$ at a temperature above Néel temperature (T$_N$= 21 K) and large negative MR below $\sim$ 3T$_N$, reported earlier for the polycrystals, are reproducible even in single crystals. Such features are generally uncharacteristic of Gd alloys. In addition, we also found interesting features in other data, e.g., two-step first-order-like metamagnetic tra…

Negative magnetoresistance in La(0.6)Y(0.1)Ca(0.3)MnO(3): Evidence for charge localization governed by the Curie-Weiss law

Colossal negative magnetoresistance Δρ(T,B) observed in La(0.6)Y(0.1)Ca(0.3)MnO(3) at B=1T shows a nearly perfect symmetry around T_0=160K suggesting a universal field-induced transport mechanism in this material. Attributing this symmetry to strong magnetic fluctuations (triggered by the Y substitution and further enhanced by magnetic field, both above and below the field-dependent Curie temperature T_C(B)=T_0), the data are interpreted in terms of the nonthermal spin hopping and magnetization M dependent charge carrier localization scenario leading to Δρ(T,B)= -ρ_s(1-exp(-γM^2)) with M(T,B)=…

The magnetoresistive behavior of Cr-doped manganites Pr0.44Sr0.56MnO3

A complex structural, magnetic and electric transport investigation shows that the Cr doping on Mn sites in the A-type antiferromagnet Pr0.44Sr0.56MnO3 provokes a non-uniform magnetic state with coexisting FM and AFM regions. Irrespective of the ratio of magnetic phases, the samples exhibit a non-metallic behavior of resistivity and thermopower, pointing to the nanoscopic nature of the phase separation. A particularly large magnetoresistance encountered in a broad range of temperatures for samples with Cr doping of 4 - 6 % supports such idea.

通过引入磁性 CrSb 提升 $p$ 型 BiSbTe 的热电性能

Enhanced Thermoelectric Performance of $p$-type BiSbTe Through Incorporation of Magnetic CrSb

本研究通过在 $p$ 型 Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ 中引入反铁磁半导体 CrSb，利用磁性粒子的拖曳效应提高热电势并降低热导率，在 325 K 下实现约 1.4 的峰值 $zT$ 值，证明引入磁性第二相可提升热电性能。

Electron transport and thermoelectric properties of layered perovskite LaBaCo2O5.5

We have investigated the systematic transport properties of the layered 112-type cobaltite LaBaCo2O5.5 by means of electrical resistivity, magnetoresistance, electroresistance and thermoelectric measurements in various conditions. In order to understand the complex conduction mechanism of LaBaCo2O5.5, the transport data have been analyzed using different theoretical models. The system shows semiconductor-semiconductor like transition (TSC) around 326K, corresponding to ferromagnetic transition and in the low temperature region resistivity data follows the Motts variable range hopping model. In…

LaMnO3+d的微波辅助合成：利用微波功率调控物理性质

Microwave-assisted synthesis of LaMnO3+d: Tuning physical properties with microwave power

本研究通过微波辐照合成LaMnO3+d，发现增大微波功率可使顺磁-铁磁转变更急剧、低温电阻率显著降低，并在1600 W下引发绝缘体-金属转变及最优磁电性能，证明微波功率可有效调控材料物理性质。

Anomalous Nernst effect in La0.5Ca0.5Coo3

We report the occurrence of the anomalous Nernst effect (ANE) in polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC = 147 K and resistivity shows non-metallic behavior above and below the TC with only a small negative magnetoresistance (~2%) around TC. Field dependence of magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which indicates the presence of magnetically heterogeneous ground state consisting of ferromagnetic and non-ferromagnetic phases. The field depen…

Magnetocaloric effect and Magnetothermopower in the room temperature ferromagnet Pr0.6Sr0.4MnO3

We have investigated magnetization(M), magnetocaloric effect(MCE) and magnetothermopower(MTEP) in polycrystalline Pr0.6Sr0.4MnO3, which shows a second-order paramagnetic to ferromagnetic transition near room temperature (TC = 305 K). However, field-cooled M(T) within the long range ferromagnetic state shows an abrupt decrease at TS = 86 K for H < 3 T. The low temperature transition is first-order in nature as suggested by the hysteresis in M(T) and exothermic/endothermic peaks in differential thermal analysis for cooling and warming cycles. The anomaly at TS is attributed to a structural trans…

Transport properties and magnetic field induced localization in the misfit cobaltite [Bi$_2$Ba$_{1.3}$K$_{0.6}$Co$_{0.1}$]$^{RS}$[CoO$_2$]$_{1.97}$ single crystal

Resistivity under magnetic field, thermopower and Hall coefficient are systematically studied for [Bi$_2$Ba$_{1.3}$K$_{0.6}$Co$_{0.1}$]$^{RS}$[CoO$_2$]$_{1.97}$ single crystal. In-plane resistivity ($ρ_{ab}$(T)) shows metallic behavior down to 2 K with a $T^2$ dependence below 30 K; while out-of-plane resistivity ($ρ_{c}(T)$) shows metallic behavior at high temperature and a thermal activation semiconducting behavior below about 12 K. Striking feature is that magnetic field induces a ln(1/$T$) diverging behavior in both $ρ_{ab}$ and $ρ_{c}(T)$ at low temperature. The positive magnetoresistance…