摘要:

Both multistep wafer‐annealed (MWA) and ingot‐annealed semi‐insulating (SI) GaAs wafers, grown by the Czochralski technique, are characterized by using normalized thermally stimulated current (NTSC) spectroscopy. Two main NTSC traps,T3at 200 K andT5at 140 K, which are thought to be related to arsenic vacancy defects, are found to be largely suppressed by MWA processes, especially by a new MWA process. Concomitant with a decrease of these traps, a significant increase of the threshold electrical field for both the thermal quenching ofT5and the low‐temperature photocurrent saturation has been observed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117278

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of carbon on TlBa2Ca2Cu3Oxphase formation in the TlF–Ba2Ca2Cu3Ozsystem were investigated by varying the carbon contents in Ba2Ca2Cu3Ozprecursor powders that were mixed with TlF and reacted to form the superconducting phase. It was found that carbon induced Tl2Ba2Ca2Cu3Oyphase formation resulting in superlattices formed byc‐axis intergrowths between TlBa2Ca2Cu3Oxand Tl2Ba2Ca2Cu3Oy. The superlattices were highly regular and uniform throughout the samples. While TlBa2Ca2Cu3Oxwas the main phase at low carbon content (0.231 wt %), Tl2Ba2Ca2Cu3Oybecame the dominant phase at high carbon content (0.472 wt %) even with a 1:2:2:3 (Tl:Ba:Ca:Cu) starting composition. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117279

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

HgBa2Ca2Cu3Oy(Hg‐1223) films with a thickness of 1–2 &mgr;m andTc(zero)∼130 K have been fabricated by utilizing a spray pyrolysis technique. X‐ray diffraction indicates that the films consist of predominantly Hg‐1223 phase grains withc‐axis orientation. Moreover, the oscillation photograph taken by a Weissenberg camera confirms that the film grains are in‐plane aligned and epitaxially grown on SrTiO3. In electrical transport measurements, the as‐fabricated film exhibits aTc(zero) of 123 K, and a zero‐fieldJcof 3.7×105A/cm2at 77 K. Additional post‐annealing at 320 °C for 50 h in flowing oxygen has improved the transport properties asTc(zero)∼130 K andJc∼4.4×105A/cm2(77 K, 0 T). ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117280

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Magnetic force microscope (MFM) profiles of domain walls (DWs) in magnetite were measured using commercially available MFM tips. Opposite polarity profiles of a single DW segment were obtained by magnetizing the MFM tip in opposite directions perpendicular to the sample surface. During a measurement, the field of the tip locally magnetized the DW, resulting in a more attractive tip‐sample interaction. The difference between opposite polarity DW profiles provided a qualitative measurement of the reversible changes in DW structure due to the localized field of the MFM tip. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117281

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The structure, Curie temperature, and magnetostriction of R1−xPrxFe1.85and R0.7Pr0.3Fey(R=Dy0.7Tb0.3,x≤0.5, 1.55≤y≤1.85) alloys were investigated. The matrix of R1−xPrxFe1.85alloys is the MgCu2‐type cubic (Dy,Tb,Pr) Fe2and the second phase was found to be (Dy,Tb,Pr) Fe3whenx≤0.3. Whenx>0.4, (Dy,Tb,Pr)Fe3is the main phase with the PuNi3‐type structure and (Dy,Tb,Pr) Fe2becomes the minority phase. In the range of 0.3<x≤0.4, both MgCu2‐ and PuNi3‐type structures coexist. The R0.7Pr0.3Feyalloys contain a small amount of (Dy,Tb,Pr) Fe3phase wheny>1.55, which increases with increasingy. Wheny=1.55, the alloy is essentially single phase with the MgCu2‐type cubic structure. The lattice parameter of (Dy,Tb,Pr)Fe2compound for R1−xPrxFe1.85alloys increases slowly with increasingxwhenx≤0.3, and sharply increases whenx>0.3. The Curie temperature of the alloys decreases steadily with increasing Pr content. The magnetostrictions of R1−xPrxFe1.85and R0.7Pr0.3Feyalloys decrease with increasing Pr content and Fe content, respectively. The largest magnetostriction at room temperature was found in the alloy R0.7Pr0.3Fe1.55(1480×10−6atH=796 kA/m). ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117282

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Enhanced low field magnetoresistance (MR) in Nd0.7Sr0.3MnO3(NSMO) has been achieved by using high‐Tcsuperconducting flux focusing devices made of YBa2Cu3O7(YBCO)/NSMO heterostructures. Two kinds of flux focusing schemes, gap, and washer devices, have been used where an applied magnetic field is expelled from patterned YBCO pads and focused onto a bridge of NSMO film. Using such a magnetic lens, at temperatures below 77 K ∼800% enhancement in MR=−(RH−R0)/R0was observed for different samples. This corresponds to more than 10% change in the MR of NSMO in the presence of 200 G. For the maximum MR response in NSMO, the YBCO/NSMO heterostructures were deposited on (100) LaAlO3substrate by pulsed laser depositioninsituso that the peak resistance temperature (Tp) of NSMO was below the superconducting transition temperature (Tc) of YBCO. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117283

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A micromachining process, using ion track etching in combination with lithographic patterning, is presented. The technique employs a substrate pre‐irradiated with swift heavy ions and uses a conventional lithographic technique to control the access of a track‐selective etching medium to the ion tracks. Experimental results show the possibility of generating high aspect ratio structures in virtually any direction in single crystalline quartz, which otherwise exhibits a strong ‘‘natural’’ anisotropy to conventional wet etching. In this way complex, three‐dimensional quartz structures of 80 &mgr;m height with vertical or pre‐defined inclination angles of the walls were produced. The process can be applied to other, even highly radiation resistant, dielectric materials such as mica and organic polymers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117284

出版商:AIP    

年代:1996

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.118163

出版商:AIP    

年代:1996

数据来源: AIP