Zhihe Wang

Magnetocaloric effect in perovskite manganites La0.7−xNdxCa0.3MnO3 and La0.7Ca0.3MnO3

In perovskite manganites La0.7−xNdxCa0.3MnO3 (x=0, 0.05, 0.1, 0.15, and 0.20) prepared by the sol–gel technique, large magnetocaloric effects have been observed. The maximum of the magnetic entropy change peaks at the magnetic ordering temperature. Compared to La0.7Ca0.3MnO3, an enhancement of the magnetocaloric effect has been obtained in the samples with Nd3+ dopant (for La0.5Nd0.2Ca0.3MnO3, the maximum of ΔSM is about −2.31 J/kgu2009K).

Charge-oscillation-induced light transmission through subwavelength slits and holes

We present a concrete picture of spoof surface plasmons (SSPs) combined with cavity resonance to clarify the basic mechanism underlying extraordinary light transmission through metal films with subwavelength slits or holes. This picture may indicate a general mechanism of metallic nanostructure optics: When light is incident on a nonplanar conducting surface, the free electrons cannot move homogeneously in response to the incident electric field, i.e., their movement can be impeded at the rough parts, forming inhomogeneous charge distributions. The oscillating charges and dipoles then emit photons (similar to Thomson scattering of x rays by oscillating electrons), and the interference between the photons may give rise to anomalous transmission, reflection, or scattering.

Magnetic entropy change in perovskite manganites La0.65Nd0.05Ca0.3Mn0.9B0.1O3 (B=Mn, Cr, Fe)

Abstract We have investigated the effect of B-site dopant on magnetic entropy change in perovskite manganite samples of La0.65Nd0.05Ca0.3MnO3, La0.65Nd0.05Ca0.3Mn0.9Cr0.1O3, and La0.65Nd0.05Ca0.3Mn0.9Fe0.1O3 prepared by sol–gel technique. The maximum ΔSH is in the order of −1.68xa0J/kgxa0K and peaks at Curie temperature for La0.65Nd0.05Ca0.3MnO3 upon 10xa0kOe applied field change. For the sample with B-site dopant, a decrement of the maximum magnetic entropy change has been observed.

Realizing High Figure of Merit in Phase-Separated Polycrystalline Sn1-xPbxSe.

Solid-state thermoelectric technology, interconverting heat to electrical energy, offers a promising solution for relaxing global energy problems. A high dimensionless figure of merit ZT is desirable for high-efficiency thermoelectric power generation. To date, thermoelectric materials research has focused on increasing the materials ZT. Here we first fabricated phase-separated Sn1-xPbxSe materials by hydrothermal synthesis. We demonstrate that the simultaneous optimization of the power factor and significant reduction in thermal conductivity can be achieved in the phase-separated Sn1-xPbxSe material. The introduction of the PbSe phase contributes to improvement of the electrical conductivity and power factor of the SnSe phase. Meanwhile, nanoscale precipitates and mesoscale grains define all-scale hierarchical architectures to scattering phonons, leading to low lattice thermal conductivity. These two favorable factors lead to remarkably high thermoelectric performance with ZT ∼ 1.7 at 873 K in polycrystalline SnSe + 1% PbSe along the pressing direction, which is a record-high ZT for SnSe polycrystals. These findings highlight the prospects of realizing highly effective solid-state thermoelectric devices.

Room temperature large magnetoresistance and magnetocaloric properties of La0.78Ag0.22MnO3 film

Abstract Room temperature large magnetoresistance and magnetocaloric properties in La 0.78 Ag 0.22 MnO 3 film prepared by pulsed laser deposition have been reported. Giant magnetoresistance of 24.5% and 60.1% were obtained at 260xa0K in a magnetic field of 1 and 8xa0T, respectively. The maximum value of the magnetic entropy change corresponding to a magnetic field variation of 1xa0T for La 0.78 Ag 0.22 MnO 3 is about −2.22xa0J/kgxa0K.

The effect of average A-site cation radius on TC in perovskite manganites

Abstract Three series of samples Ln 0.7 T 0.3 MnO 3 (I), Ln 0.7 T 0.3 Mn 0.9 Cr 0.1 O 3 (II), and Ln 0.7 T 0.3 Mn 0.9 Fe 0.1 O 3 (III) (Ln=La, (La, Nd), (La, Y), T=Ca, CaSr, Sr) were prepared by sol–gel technique. The effect of the average A-site cation radius 〈 r A 〉 on the ferromagnetic transition temperature T C has been investigated. T C was obtained from M – T curves measured by vibrating sample magnetometer. For a little Nd 3+ doped at the A-site, the T C of Ln 0.7 T 0.3 MnO 3 (I) drops linearly with decreasing 〈 r A 〉 (1.18xa0A r A 〉 T C values than series I due to the weakening of the influence of double-exchange interactions upon substituting Fe and Cr for Mn.

Plasmonic antenna array at optical frequency made by nanoapertures

We show here that the plasmonic array based on nanoapertures in ultrathin silver film radiates at optical frequency and behaves as an optical antenna array (OAA). The far-field radiation originates from the coherent superposition of plasmonic emissions on each bank of the aperture. The radiation of OAA presents a strong directivity, which depends on the in-plane rotation of aperture array, and on the polarization and incidence angle of the excitation light as well. We suggest that these features have potential applications in photovoltaics, light-emitting devices, and optical sensors.

Selectable-frequency and tunable-Q perfect transmissions of electromagnetic waves in dielectric heterostructures

Multiple perfect transmissions of electromagnetic waves are found in the photonic band gap of the symmetric dielectric heterostructures (SDH) constructed as (AB)nBm(BA)n, where A and B stand for different dielectric materials, and m and n are the repeating numbers of the units. The photonic frequency and the mode number of resonant transmissions therein can be manipulated by varying m, and the quality factor Q of the perfect transmission peak increases exponentially with increasing n. These features are experimentally demonstrated in a SDH of TiO2/SiO2 for visible and near infrared light. The possible applications of SDH for the wavelength division multiplexing system are discussed.

Magnetic entropy change in La0.54Ca0.32MnO3−δ

A La-deficient manganite perovskite sample La0.54Ca0.32MnO3−δ was prepared by conventional solid-state reaction method. The Curie temperature TC is 272 K, about 10 K higher than that of La1−xCaxMnO3. A large magnetic entropy change has been observed and the maximum −ΔSM≈2.9u200aJ/kgu200aK appears at its Curie temperature upon a 0.9 T magnetic field change. The easy fabrication and higher chemical stability make La0.54Ca0.32MnO3−δ a suitable candidate as a working substance in magnetic refrigeration technology.

Enhancement of the spin entropy in NaxCo2O4 by Ni doping

The effects of Ni doping on the spin entropy in NaxCo2O4 (x=1.2) has been carefully studied. A strong magnetic-field suppression of the thermopower indicates the emergence of large spin-entropy effect. The magnetothermopower increases with increasing Ni doping level, suggesting that Ni doping improves the spin entropy of NaxCo2O4. Based on analysis of x-ray absorption spectra, we propose a spin-entropy competition mechanism to explain well the spin-entropy enhancement.