摘要:

We have measured the dependence of the transport critical‐current density on magnetic fields and temperatures close toTcof high‐JcBi(2223) Ag‐sheathed pressed (Jc=2.1×104A/cm2, 77 K, 0 T) and cold rolled tapes (Jc=1.8×104A/cm2, 77 K, 0 T). It is found that the transport critical current of the two kinds of tapes follows the relationJc=Jco(1−&agr;T+&bgr;T2). The results can be explained according to the thermally activated flux creep model. The dependence ofJconHfor two kinds of tapes is compared asHis parallel and perpendicular to the tape surface. It is found that the cold rolled tapes have a weaker field dependence ofJcfor theH⊥tape surface at higher fields (≳0.2 T). The difference ofJc(H) between the pressed and cold rolled tapes seems to originate from the difference in their microstructure defects. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113504

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A method was developed to melt join two YBa2Cu3Oxdomains together. After melt joining, the scanning electron microscopy analysis did not reveal any interfaces near the original domain contact surfaces. Both samples with equal geometry and orientation before and after the melt‐joining process exhibited the same magnetic hysteresis, indicating that the melt‐joined sample was strongly coupled. Also discussed is a possible domain growth mechanism during the melt‐joining process. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113505

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the dc current–voltage characteristic of high temperature superconducting microbridges. When a dc voltage is applied to a microbridge, it switches to a lossy state due to the formation of a hotspot in the bridge. We have measured the length and temperature of the hotspot as a function of the applied voltage, and have developed a thermal model to explain its steady state behavior. The hotspot has a flat‐topped temperature profile, with the maximum temperature independent of the applied voltage. The length of the hotspot, and hence the bridge resistance, increases linearly with the applied bias, so the current is independent of the applied voltage once switching has occurred. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113506

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An approach is demonstrated for lithographic fabrication of perpendicular current magnetoresistance devices which avoids the necessity of postprocess ‘‘trimming’’ of electrical leads. Magnetoresistance properties are investigated as a function of device size, magnetic layer thickness, and temperature. It is found that in some cases the current distribution in the microstructures change substantially with temperature resulting in a negative temperature coefficient of resistivity. It is also shown that the devices’ own magnetic fields have a dramatic effect on magnetoresistance properties. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113507

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A magnetic force microscope (MFM) was used to image topography and magnetic forces from a chain of submicron single magnetic domain particles produced by and contained in isolated magnetotactic bacteria. The noncontact magnetic force microscope data were used to determine a value for the magnetic moment of an individual bacterial cell, of order 10−13emu, consistent with the average magnetic moment of bacteria from the same sample, obtained by superconducting quantum interference device magnetometry. The results represent the most sensitive quantification of a magnetic force microscope image to date. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113508

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a technique for measuring the coercivity of magneto‐optical and perpendicular recording media on a submicron scale using a magnetic force microscope and an electromagnet. Co–Cr coated silicon tips were used to write and image magnetic bits down to 150 nm in diameter. Bits were written when the sum of the tip stray field and an external fieldHextexceeded the local, or ‘‘point’’ coercivity. Media can be characterized by a continuous write probabilityPw(Hext) which differs significantly from bulk hysteresis loops. For an intermediate field range, writing was intermittent (0<Pw<1) due to spatial variations in media properties. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113509

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A metrological application is reported of the single electron tunneling (SET) phenomena: a precise measurement of the ratio of two cryogenic capacitors. The measurement used a superconducting SET electrometer as the null detector for a capacitance bridge. A 3‐ppm level of imprecision has been achieved in the measurement of the capacitance ratio from 100 to 1000 Hz. Further improvements can be made in the attempt to obtain an imprecision of 10−8at lower frequencies, sufficient for the metrological measurement of capacitance or the fine‐structure constant using a SET pump. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113510

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured by micro‐Raman spectroscopy the surface enhanced Raman scattering (SERS) spectra of about 2 monolayers of C70on Ag surface. New Raman bands of the fullerene molecule have been found. The time evolution (from C70to amorphous carbon) of the SERS spectra, under high laser power density illumination in air, provides evidence of photochemical reactions. New bands in the Raman spectra appearing with the time have been attributed to intermediate products of these photochemical reactions. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113511

出版商:AIP    

年代:1995

数据来源: AIP