Shunyi Zhang

Magnetocaloric properties of Ag-substituted perovskite-type manganites

Abstract Magnetic entropy change larger than that of gadolinium has been observed near room temperature in polycrystalline of La 0.8 Ag 0.2 MnO 3 perovskite-type manganite. The large magnetic entropy change produced by the abrupt reduction of magnetization is associated with a first-order phase transition of the sample near the Curie temperature. This phenomenon indicates that perovskite manganites have some potential applications for magnetic refrigerants in an extended high-temperature range.

Mechanisms of laser drilling of metal plates underwater

Several metal plates with different thickness including copper, iron, aluminum, and stainless steel have been drilled in the surroundings of air and water, respectively, by a Q-switched pulsed Nd:yttrium–aluminum–garnet laser. It is observed that for the same metal plate less energy is needed to drill a hole in water than that in air, and the surface morphology of hole drilled in water is improved greatly than that in air by comparison of the scanning electron micrographs. The underlying mechanisms behind the efficiency and quality enhancement in water are further investigated by means of optical beam deflection technique. The experimental results show that due to the water confinement the peak amplitude and duration of the laser-ablation-generated impact underwater is much larger than that in air. During the underwater laser drilling, besides laser ablation effect, both the first and second liquid-jet-induced impulses by cavitation bubble collapse in the vicinity of a solid boundary are also observed and...

Synthesis and magnetostriction of melt-spun Pr1−xTbx(Fe0.6Co0.4)2 alloys

Pseudobinary Pr1−xTbx(Fe0.6Co0.4)2 (0⩽x⩽0.4) cubic Laves single phases have been synthesized by melt spinning and subsequent annealing. Their structure, magnetic properties and stability have been investigated. The composition, at which the anisotropy of Pr1−xTbx(Fe0.6Co0.4)2 is compensated, is close to x=0.1. The spontaneous magnetostrictions λ111 of Pr0.9Tb0.1(Fe0.6Co0.4)2 and Pr0.8Tb0.2(Fe0.6Co0.4)2 are larger than 1500×10−6 and 1900×10−6, respectively. Pr1−xTbx(Fe0.6Co0.4)2 (0.1⩽x⩽0.4) ribbon-based materials with 3% epoxy resin combine high magnetostriction with significant magnetic coercivity. Pr0.9Tb0.1(Fe0.6Co0.4)2 is a promising magnetostrictive material.

Excitations of thermoelastic waves in plates by a pulsed laser

The method of the eigenfunction expansion, also known as the expansion in normal modes, is employed to study numerically the axisymmetric excitation of the thermoelastic waves in plates by a pulsed laser. This method gives a systematic treatment and allows one to investigate not only the quasistatic and dynamic thermoelastic responses of pulsed photothermal deformation on the time scale of 1 μs, but also the thermoelastic generation of longitudinal, transverse, and surface acoustic waves in thick materials, as well as the excitations of the Rayleigh-Lamb wave modes in thin plates. The formalism is particularly suitable for waveform analyses of the excitations of transient Lamb waves in thin plates because one needs only to calculate the contributions of several lower eigenmodes. The numerical technique provides a quantitative tool for the experimental determination of material properties, especially the mechanical and elastic properties of free-standing films and thicker sheet materials by thermoelastic detection.

Low-temperature magnetic properties of R0.7Pb0.3MnO3 (R=Nd and La) single crystals

Structural and magnetic properties of the Gd(Fe1-xNix)(11.3)Nb-0.7 compounds with x ranging from 0 to 0.175 have been investigated by means of X-ray diffraction and magnetic measurements. All compounds investigated crystallize in the ThMn12-type structure. Lattice parameters and unit-cell volume decrease slightly with increasing x. The substitution of Ni for Fe leads to a clear increase of Curie temperature from 596 K at x = 0.0 to 656 K at x = 0.175. The anisotropies at room temperature of these compounds are of easy axis. The anisotropy held B-a decreases clearly with increasing Ni content. The decrease speed of B-a with Ni content at 5 K is faster than at room temperature

Microstructure investigation of Fe/Al2O3/Fe tunneling junction

A series of Fe/Al2O3/Fe tunneling junction samples were prepared by ion beam sputtering technique. After deposited, the Al layers in a series of samples were exposed to the air for 24–100 h to obtain Al2O3 layers (100 A) with different oxidation quality. A tunneling magnetoresistance (TMR) value of 5.89% was observed in the sample with the Al layer oxidized for 72 h. The I–V curve of this sample shows a nonlinear relationship, indicating the existence of well metal–insulator contact in the sample. The microstructures of these samples were analyzed by using x-ray photoelectron spectroscopy. The results show that good Al2O3 layers are formed in all samples, but there exists an interdiffusion interface between the Fe and Al2O3 (with Al metal inclusions) layer which greatly influences the TMR effect.

Investigation of the effect of laser treatment on the longitudinal and transverse velocity of an aluminum alloy

The velocities of longitudinal and transverse waves for aluminum alloy 2024-T62 shocked by a high-power Nd: Glass laser are investigated by a laser ultrasonics method. The results show that the velocity of the longitudinal wave measured after the laser-shock processing increases at the center and decreases at the edge of the laser-shocked area (LSA). The maximum relative increase is 28% and the maximum decrease up to 10%, when compared with that measured before the alloy was shocked by laser processing. The velocity of the transverse wave decreases at any position within LSA, the maximum relative decrease being 13%. The decrease at the edge of LSA is larger than that at the center.

Finite element simulation of the film spallation process induced by the pulsed laser peening

The laser spallation technique for measuring the interface strength between a coating and a substrate is similar to laser shock peening, in which the stress wave induced by laser shock cause debond on the interface between a hard coating with micron thickness and a metal substrate. According to the modified experiment setup of the laser spallation technique, finite element analysis simulated the process of the film spallation by taking the laser loading as a direct input. We presented a numerical model of finite element that the laser spallation process includes two related, but uncoupled procedures. One was transient heat transfer in a two-layer medium. The other was the related transient elastic wave propagation in the same two-layer media, which was the result of the thermal misfit by transient heating. Based on the threshold of film spallation, we analyzed the process of laser shocking to study the propagation of stress wave and evaluate the spall resistance of sputtered films. The analysis result sho...

Large magnetostriction effect in bulk (La1−xSmx)2/3Sr1/3MnO3

A series of polycrystalline bulk (La1−xSmx)2/3Sr1/3MnO3 samples over a wide composition range (x=0,0.1,0.33,…,1) was prepared by solid-phase reaction sintering technique. The x-ray diffraction pattern indicates that all the samples have an orthorhombically distorted perovskite structure. A large linear magnetostriction with a value up to −180×10−6 was observed at the temperature of 77 K under the maximum magnetic field of 1.5 T. The linear magnetostriction and magnetoresistance effect of our samples has similar dependence on the Sm content x. At room temperature, the sample with a Curie temperature of 320 K, and a Sm content of x=0.33, shows both maximum linear magnetostriction value of −40×10−6 and a maximum magnetoresistance value of −12%.

Intergranule interaction in magnetic granular films

Abstract Magnetic granular films consist of nanoscale magnetic granules embedded in an insulator or in an immiscible metal. The advantage of granular films is that there exists abundant interface between magnetic granules and the matrix with unique microstructures. The physical properties in these systems can be tailored by adjusting the composition, volume fraction of constituent materials, and preparation conditions. In this paper, some results on domain observation in Co 35 (SiO 2 ) 65 granular film and spin-wave resonance in FeSiO 2 granular film will be presented, which may be helpful to understand the intergranule interaction in magnetic granular systems.