Chuanjian Wu

Great enhancement of pyroelectric properties for Ba0.65Sr0.35TiO3 films on Pt–Si substrates by inserting a self-buffered layer

(100)-Ba0.65Sr0.35TiO3 (BST) films were deposited on Pt/Ti/SiO2/Si substrates using a low-temperature self-buffered layer. X-ray diffraction and atomic force microscope investigations show that the microstructure of BST films strongly depends on surface morphology of annealed self-buffered layer. The mechanism of nucleus formation and the growth initiation of BST films on self-buffered layers were proposed. It was found that the pyroelectric properties of BST films can be greatly enhanced. The pyroelectric coefficient and material merit figure of (100)-BST films are 1.16×104 μC m−2 K−1 and 2.18×10−4 Pa−1/2, respectively. The detectivity of 9.4×107 cm Hz1/2 W−1 was obtained in the (100)-BST film capacitors thermally isolated by 500 nm SiO2 films.

Relationship between Curie temperature and Brillouin function characteristics of NiCuZn ferrites

Based on Neels two-sublattice collinear model, the relationship between Curie temperature Tc and temperature characteristics of Brillouin function for NiCuZn ferrites has been studied by nonlinear fitting calculation method. According to the tetrahedral A sites and the octahedral B sites of spinel structure model which do not only contain Fe3+ but also some other multiple magnetic ions (Ni2+and Cu2+), molecular-field coefficients ωaa, ωbb, and ωab = ωba have been calculated; furthermore, the ferrimagnetism and paramagnetism Curie temperature Tc calculation formula has been modified, respectively. The magnetic moment versus temperature T (below the Curie temperature Tc) and the reciprocal of paramagnetism magnetic susceptibility 1/χm versus temperature T (beyond the Curie temperature Tc) have been investigated, respectively. The values of the calculated ferrimagnetism Curie temperature are very close to the values of the testing Curie temperature, and with the same zinc content t, the values of paramagnet...

Brillouin function characteristics for La-Co substituted barium hexaferrites

La-Co substituted barium hexaferrites with the chemical formula of Ba1−xLaxFe12−xCoxO19 (x = 0.0, 0.1, 0.3, and 0.5), prepared by a conventional ceramic method, were systematically investigated by Raman spectra, X-ray photoelectron spectroscopy, Rietveld refinement of X-ray diffraction patterns, and vibrating sample magnetometer. The result manifests that all the compounds are crystallized in magnetoplumbite hexagonal structure. Trivalent cobalt ions prevailingly occupy the 2a, 4f1, and 12k sites. According to Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients ωbf2, ωkf1, ωaf1, ωkf2, and ωbk of La-Co substituted barium hexaferrites have been calculated using the nonlinear fitting method, and the magnetic moment of five sublattices (2a, 2b, 4f1, 4f2, and 12k) versus temperature T has been also investigated. The fitting results are coincided well with the experimental data. Moreover, with the increase of La-Co substitution amount x, the molecular-field coefficients ωbf2 and ωaf1 d...

Pb(ZrTi)0.98Mn0.02O3 weight ratio effects on the properties of Pb(ZrTi)0.98Mn0.02O3/P(VDF-TrFE) composite film and infrared detectors

The effect of Pb(ZrTi)0.98Mn0.02O3 (PZTM) weight ratio on the properties of PZTM/P(VDF-TrFE) pyroelectric composites and devices was reported in this paper. Infrared devices were fabricated using PZTM/P(VDF-TrFE) composite films with different weight ratio. The pyroelectric coefficient, the dielectric properties and the infrared absorptivity of the composite materials have been measured. It was found that the pyroelectric constant of the composite decreased as PZTM weight increased. In contrast, the dielectric permittivity increased as PZTM weight increased. Especially, the composite with 0.41 PZTM weight ratio showed the smallest dielectric loss and largest infrared absorptivity. The properties of the detectors fabricated using the composite materials with different PZTM weight ratio have been further tested. It was found that the infrared irradiation absorptivity showed great impact on the performance of the devices other than the pyroelectric coefficient and dielectric permittivity.

Calculation of exchange integrals and Curie temperature for La-substituted barium hexaferrites.

As the macro behavior of the strength of exchange interaction, state of the art of Curie temperature Tc, which is directly proportional to the exchange integrals, makes sense to the high-frequency and high-reliability microwave devices. Challenge remains as finding a quantitative way to reveal the relationship between the Curie temperature and the exchange integrals for doped barium hexaferrites. Here in this report, for La-substituted barium hexaferrites, the electronic structure has been determined by the density functional theory (DFT) and generalized gradient approximation (GGA). By means of the comparison between the ground and relative state, thirteen exchange integrals have been calculated as a function of the effective value Ueff. Furthermore, based on the Heisenberg model, the molecular field approximation (MFA) and random phase approximation (RPA), which provide an upper and lower bound of the Curie temperature Tc, have been adopted to deduce the Curie temperature Tc. In addition, the Curie temperature Tc derived from the MFA are coincided well with the experimental data. Finally, the strength of superexchange interaction mainly depends on 2b-4f1, 4f2-12k, 2a-4f1, and 4f1-12k interactions.

Ferromagnetic Resonance Study on Si/NiO/NiFe Films

Motivated by the wide application of the antiferromagnetic/ferromagnetic (FM) bilayer structures in high-frequency microwave magnetic devices, the Si/NiO/Ni81Fe19 films with different orientations of NiO buffer layer are deposited by magnetron sputtering technology. The phase, microstructure, hysteresis loop, and angular dependence of FM resonance (FMR) linewidth are investigated by X-ray diffractometer, field-emission scanning electron microscope, atomic force microscope, vibrating sample magnetometer, and electron spin resonance spectrometer, respectively. The Si/NiO(220) film has much smaller grain size than that of Si/NiO(200) film, which is beneficial to grow a high quality NiFe film on Si/NiO(220)/NiFe bilayer structures. The hysteresis loop of Si/NiO(220)/NiFe films shows an obvious exchange bias and a relatively smaller coercivity. The FMR linewidth (ΔH) of Si/NiO(220)/NiFe films is much smaller than that of Si/NiO(200)/NiFe films, which is caused by the different structural properties and morphologies of the NiO buffer layer. The Landé g factors and effective damping parameters αeff are also discussed.

Effects of the TiO2 buffer thickness on SrTiO3 (111) epitaxial films grown on GaN (0002)

SrTiO3 (STO) films have been grown on TiO2-buffered GaN(0002) substrates. The deposition process was in situ monitored by reflective high energy electron diffraction (RHEED). The deposition rate and in-plane lattice parameter of TiO2 were calculated from the oscillation curve and RHEED patterns, respectively. It was found that the TiO2 lattice parameter changed as the thickness increased, which indicated a strain relaxation process of TiO2 buffer layers during the deposition. We show that the thickness of TiO2 can significantly influence the STO growth mode, surface morphology, and crystalline quality. As the TiO2 thickness increased, the STO growth mode is changed from 3D island to 2D growth mode and finally to SK mode as revealed by RHEED. The growth mode evolution shows close relation with the surface morphology and crystalline quality of STO. STO films deposited on 2 nm thick TiO2 film show 2D growth mode and have smoothest surface and smallest full width at half maximum of the STO rocking curve. Our ...

Cation distribution and the temperature dependence of Brillouin function for nickel-substituted MnZn ferrites

In this work, one carried out the Rietveld refinement to exactly identify the cation distribution of Ni-substituted MnZn ferrites. Then, one investigated the temperature dependence of Brillouin function based on the experimental and fitting molecule magnetic moment under the Neel model of collinear-spin ferrimagnetism.

Study on the Contribution of Magnetization Mechanisms in NiZn Ferrites

In this paper, combined with a comprehensive analysis of relevant magnetic properties and magnetic domain, the change of contribution from two kinds of magnetization mechanisms was discussed.

Magnetization and X-ray absorption spectroscopy of Mn implanted Ge after flash lamp annealing

Ge-based diluted magnetic semiconductors have drawn extensive attention over the past decades due to their potential to be applied in spintronic devices and to be integrated with the mainstream Si microelectronics as well. The hole-mediated effect in diluted magnetic semiconductors provides the possibility to realize the control of magnetic properties by the electrical control of free carriers. In this contribution, we will present the magnetic properties and X-ray absorption spectroscopy of Mn implanted Ge annealed by flash lamp, which is a sub-second annealing method and compatible with chip-technology.