E.J. Tarte

Resistance of a domain wall in La0.7Ca0.3MnO3

Although colossal magnetoresistance (CMR) materials exhibit large changes in electrical resistance (up to 106%), large magnetic fields (several tesla) must be applied. To obtain a sizeable low-field effect (<102% in several millitesla), it is necessary to incorporate structural discontinuities such as grain boundaries, or other types of interfaces. The potential for applications, however, remains limited because structural discontinuities increase electrical resistance by several orders of magnitude and hence create noise. Moreover, it has proven to be difficult to fabricate structural discontinuities reproducibly. We have attempted to investigate discontinuities that are purely magnetic via transport measurements through a precisely controlled number of magnetic domain walls of known area in thin film devices of the ferromagnetic CMR perovskite La0.7Ca0.3MnO3. A sharp low-field switching seen below ∼110 K is ascribed to the formation of a precise number of magnetic domain walls, each with resistance-area...

Directly coupled superconducting quantum interference device magnetometer fabricated in magnesium diboride by focused ion beam

We report the fabrication of a directly coupled superconducting quantum interference device (SQUID) magnetometer in MgB2 using a focused ion beam to create Josephson junctions in a 70-nm-thick-film of MgB2. The SQUID shows a voltage modulation (ΔV) of 175 μV at a temperature of 10 K and operates over a temperature range from 10 to 24 K. We find excellent agreement between the measured maximum transfer functions and those predicted by theory. We have measured the magnetic flux white noise level at 20 K and 10 kHz to be as low as 14 μΦ0 Hz−1/2.

The capacitance of bicrystal Josephson junctions deposited on SrTiO/sub 3/ substrates

We have investigated the capacitance of grain boundary Josephson junctions deposited on symmetric 24/spl deg/ misoriented SrTiO/sub 3/ bicrystal substrates using hysteresis and Fiske resonances in their current voltage characteristics. Our measurements show that the total junction capacitance is proportional to the junction area. The capacitance per unit area is (140/spl plusmn/30) fF /spl mu/m/sup -2/ and this implies that the main effect of the large relative permittivity of the substrate is to scale-up the grain boundary capacitance by a factor of around 10. We also find that in the planar geometry of bicrystal grain boundary junctions the velocity of light in the junction depends upon film thickness.

DIRECT WRITING OF LOW TC SUPERCONDUCTOR-NORMAL METAL-SUPERCONDUCTOR JUNCTIONS USING A FOCUSED ION BEAM

Using a focused ion beam, we have produced superconductor-normal metal-superconductor junctions by controllably removing a portion of the top layer of a patterned superconductor-normal metal thin film. The high-quality junctions showed Josephson coupling which scaled qualitatively with barrier properties and temperature as expected. The largest product of a junction’s critical current and the normal state resistance measured is 98 μV at 4.2 K. The method has good reproducibility and could be exploited in a number of superconducting electronics applications.

Vortex channeling and the voltage–current characteristics of YBa2Cu3O7 low-angle grain boundaries

We have performed (voltage–current) V–I measurements on a thin film YBa2Cu3O7 4° [001] tilt low-angle grain boundary over an extensive range of temperatures and fields, verifying the presence of a linear characteristic. We report on the occurrence of the linear characteristic in its basic form and on the observation of V–I kinking into several, and in some cases numerous, linear segments. We interpret these findings in terms of a variation in the dissipative width at the grain boundary. Kinking from one linear V–I section to another of different gradient is described in terms of a change in the number of vortex rows being viscously channeled along the boundary.

Realization and properties of YBa2Cu3O7−δ Josephson junctions by metal masked ion damage technique

We have developed a simple process to fabricate high-TC Josephson junctions by a combination of focused ion beam milling and 100 keV H2+ ion implantation. The resistively shunted junction-like current–voltage characteristics were observed in the temperature range of 48 to 4.2 K. The devices showed clear dc and ac Josephson effects. This technique is very promising in terms of simplicity and flexibility of fabrication and has potential for high-density integration.

Fabrication of in‐plane aligned a‐axis oriented YBa2Cu3O7−x trilayer Josephson junctions

We have fabricated vertical YBa 2Cu3O7−x/PrBa 2Cu3O7−x/YBa 2Cu3O7−x (YBCO/PBCO/YBCO) Josephson junctions using in‐plane aligned a‐axis oriented YBCO multilayers on (100) LaSrGaO4(LSGO). The Tc’s of the device electrodes are typically greater than 80 K. Josephson coupling is observed for barrier thickness up to 800 A. Strong nonlinear I–V characteristics arising from the properties of PBCO are observed for thicker barrier devices. Chip to chip spread in the device characteristics may be intrinsically due to the PBCO barrier.

Realization and properties of MgB2 metal-masked ion damage junctions

Ion beam damage combined with nanoscale focused-ion-beam direct milling was used to create manufacturable superconductor–normal–superconductor type (SNS) Josephson junctions in 100-nm-thick MgB2 with TC of 38 K. The junctions show nonhysteretic current–voltage characteristics between 36 and 4.2 K. Experimental evidence for the dc and ac Josephson effects in MgB2 metal-masked ion damage junctions are presented. This technique is particularly useful for prototyping devices due to its simplicity and flexibility of fabrication and has a great potential for high-density integration.

Proximity and Josephson effects in superconductor/antiferromagnetic Nb/gamma-Fe50Mn50 heterostructures

We study the proximity effect in superconductor

Electrical properties of electron and ion beam irradiated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

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