摘要:

The in-depth distribution of the critical temperature in the YBa2Cu3O7film, predicted by our recent modeling of ion modified high-Tcweak links is checked. Removing a surface layer of the film step by step using bromine-ethanol chemical etching, we observed a nonuniform in-depth critical temperature distribution and found that the film inside becomes granular after the modification. This region with reduced connectivity may be responsible for the Josephson properties observed. A new idea for improving these weak links is reported. If two modifications with different ion energy or different ions are used, it is possible to form the conducting channel inside the superconducting film with dimensions independent from variations in the film thickness. These junctions are expected to have lower long time drift. Additionally, the channel is created in the region of the film where the film properties are superior to those near the interface. This should strongly improve the yield of the working device on the chip. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364113

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Binary SmxFe100−x(2<x<12) thin films were made by rf sputtering of the target onto preheated quartz glass substrates. Structural characterization, magnetic measurement, and microstructure observation were carried out by x-ray diffractometer, vibrating sample magnetometer, scanning electron microscope, and transmission electron microscope (TEM), respectively. Directly crystallized films were synthesized at substrate temperature higher than 400 °C and the main phase of the films is the ThMn12-type tetragonal phase with lattice parametersa=8.65 Å andc=4.78 Å. Films have the predominant [111] and [001] crystallographic texture when the substrate temperature is lower and higher than 600 °C, respectively. The perpendicular magnetization measured under the applied field of 22 kOe is about 30&percent; higher than the saturation magnetization of bulk SmFe11Ti. Coercivities of about 4.0 kOe can be obtained in the substrate temperature range between 430 and 550 °C with grain size of 0.2–0.3 &mgr;m. Cross-sectional TEM microstructure observations show significant columnar structures in the films. The [001] texture formed in the films is also clearly reflected by the planar and cross-sectional TEM diffraction patterns. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364114

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single domain &egr;-Fe3N nitride particles have been synthesized by chemical reduction followed by nitridation at 823 K. The &egr;-Fe3N phase crystallizes in hexagonal structure with unit cell parameters,a=2.70 Å andc=4.39 Å. There is a reduction of unpaireddelectrons for intraband polarization as the nitrogen contributes to the density of states and thus results in lowering of magnetic moments. The reduction of intrinsic magnetizations and Curie temperatures with decreasing particle size is attributed to canted spin structure predominantly at the surface compared to the bulk of the particles. Chemisorption of oxygen results in the formation of oxynitride layer at the surface with a ferromagnetic coupling to the spins in the core of the particle. Mo¨ssbauer study of &egr;-Fe3N particles exhibits the coexistence of ferromagnetic and superparamagnetic particles and corroborates the observed magnetic properties. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364115

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The texture and surface/interface topological effects on the exchange fieldHexand coercivityHcin rf-sputtered NiO/NiFe bilayers were studied. The NiO/NiFe bilayers with NiO crystalline textures of (111), (200), and (220), and different surface/interface roughness, were fabricated by changing the sputtering conditions. TheHexof the NiO/NiFe bilayers was inversely proportional to the thickness of NiFe. The NiO/NiFe bilayers with different NiO textures of (111) dominant, (200) dominant, or combinations of (111), (200), and (220), respectively, showed almost the same dependence ofHexon NiFe thickness. Thus,Hexwas insensitive to the texture of NiO films. The surface/interface roughness has a significant effect onHcof the NiO/NiFe bilayers. By controlling the sputtering process, NiO (45 nm)/NiFe (10 nm) bilayers with aHexof 39 Oe, aHcof 4.1 Oe, and anHex/Hcratio of 9.51 could be obtained. A new parameter ofHex/Hcwas introduced to describe the exchange coupling and coercive properties in ferromagnet/antiferromagnet coupled bilayers. A largeHex/Hcratio is very desirable for spin-valve structures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364116

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fe (111) single crystal films have been grown on GaAs (111) by the sputter-beam method. Reflection high energy electron diffraction and x-ray diffraction measurements have revealed excellent aligned epitaxial growth of the Fe (111) film on GaAs. No evidence of preferential diffusion of As atoms into the deposited Fe layers has been found in the depth profile of Auger electron spectra. Magnetic measurements clearly show that the Fe (111) film has nearly ideal threefold symmetric anisotropy and exhibits isotropic initial permeability in the film plane, as predicted by theory.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364117

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of eddy currents and ferromagnetic resonance (FMR) on the frequency dependence of the permeability of FeTaN thin films is studied. An equation is given that describes the combination of these two effects. The agreement between the theoretical calculations and the experimental data is excellent. Already at 1 MHz the imaginary part of the permeability is significantly changed by FMR. Above 10 MHz the real part of the permeability is decreased by FMR. The combined effect is best observed in extremely high permeable, 1 &mgr;m thick films. A value for the ferromagnetic damping constant is obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364118

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Lanthanum modified lead zirconate titanate ceramics with La/Zr/Ti ratios of 6/40/60, 12/40/60, 5/65/35, and 9/65/35 have been studied by polarized Raman scattering. In the two former (tetragonal-type) compositions, selection rules were rather well defined and allowed an assignment of the Raman lines at lower temperature. These selection rules disappeared for 6/40/60 but remained for 12/40/60 even at higher temperatures. The behavior of the two latter (rhombohedral-type compositions) was quite different. No assignment of lines could be done. In addition, the spectra recorded in parallel and crossed polarizations were almost identical for 5/65/35 regardless of temperature. A very smeared paraelectric to ferroelectric transition was evidenced by Raman intensity measurements for this composition. On the contrary, selection rules were always present for the relaxor composition 9/65/35 which were similar to those for 12/40/60 and 6/40/60. This suggests that both tetragonal and rhombohedral-type local polar order is present for 9/65/35. The spectra of the field induced ferroelectric phase for 9/65/35 revealed no selection rules, similar to 5/65/35. This is attributed to the onset of only medium range ferroelectric order. Finally, Raman spectra recorded on powders of every composition did not reveal any selection rules, suggesting that intergranular effects might play a significant role in the behavior of these materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364119

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The complex dielectric responses of various La-modified lead zirconate titanate ceramic specimens have been measured under various ac drive and dc bias conditions. Investigations were performed for different La concentrations on specimens with Zr/Ti ratios of 40/60 and 65/35. These investigations demonstrated that the influence of increasing ac drive and dc bias are in opposition: increasing drive results in an increase in the dielectric constant, whereas increasing bias results in a decrease. Investigations as a function of La content revealed a strong decrease in the ac-induced nonlinearities with increasing La content in the compositional range near a crossover between micron-sized domains and tweedlike structures. The ac drive dependent dielectric data were then empirically fitted to a power series expansion in the ac field. An anomalous change in sign of the second-order nonlinearity was found for lower La-content compositions near the temperature of the dielectric maximum. It is believed that this change in sign results from a suppression of ferroelectric order and the stabilization of a paraelectric state at temperatures close to the ferroelectric phase transformation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364120

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A technique for observation of 180° domains in ferroelectric crystals is demonstrated by the use of the second harmonic generation (SHG) microscope. The phase reversal of the SH wave accompanying inversion of spontaneous polarization is exploited to visualize domains. Interference between SH waves converts the phase information to the SH contrast. The domain mapping is achieved in LiNbO3and LiTaO3by nonlinear coefficientsd33andd22under the microscope, which enables the characterization of a periodically poled structure in quasi-phase-matched wavelength converters in a nondestructive way. The validity of the technique is proved by another characterizing tool of destructive etching. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364121

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Strontium barium niobate, Sr0.6Ba0.4Nb2O6(SBN40) ceramics were prepared by the mixed oxide route; specimens sintered at 1300 °C–1450 °C for 2–4 h had densities of ∼95&percent; theoretical. The use of “conventional’’ conditions (1300 °C; ∼200 °C below the melting temperature) gave rise to a duplex structure comprising a mixture of small grains and abnormally large grains (in excess of 100 &mgr;m). Transmission electron microscopy studies revealed a Nb-rich, Ba-poor phase at the grain boundaries; the low melting temperature of this phase caused localized liquid phase sintering, resulting in abnormal grain growth. Dual-stage sintering (sintering at 1250 °C for 4 h, followed by sintering at a temperature in the range 1350 °C–1450 °C) inhibited abnormal grain growth. The use of a fast heating rate (600 °C/h) and dual-stage sintering (1250 °C and 1450 °C) yielded samples with good transparency and preferential orientation along thec-direction of the tetragonal unit cell. The dielectric properties depended sensitively on microstructure. Specimens with the highest densities had the highest relative permittivities (2400–2750); specimens with more uniform distribution of grain sizes had sharper dielectric maxima. A mechanism for abnormal grain growth is proposed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364122

出版商:AIP    

年代:1997

数据来源: AIP