摘要:

We propose a design for planar multi-turn flux transformer for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. This transformer is integrated with a coplanar resonator, e.g., on a1 cm2LaAlO3substrate. Its pickup loop is connected with two input coils, separate for dc (low-frequency) and rf currents. A double-hole washer SQUID is coupled to these coils in a flip-chip configuration to form a magnetometer. The separation of rf and dc current paths in the transformer made it possible to demonstrate the rf SQUID magnetometer operation. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121254

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have developed a process to fabricate planar high-TcJosephson junctions using nanolithography and a 200 keV ion implanter. Conduction occurs in the ab plane and is interface free. We can systematically tune devices to operate at temperatures between 1 K and theTcof the undamaged superconducting material by varying the length of the weak link and by changing the amount of ion damage. All of the devices showed clear dc and ac Josephson effects. Measurement ofR(T)andIc(T)of the weak links revealed trends which were consistent with a proximity effect. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121255

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Single crystals ofNd1Ba2Cu3Oy(Nd123) high-temperature superconductors have been studied using an ultrahigh vacuum scanning tunneling microscope/spectroscopy system at room temperature. A square lattice with average lattice spacings of4×4 Å2has been observed on the surfaces of the single crystals without any surface protections or treatments. The as-prepared surfaces are found to be terminated by the CuO chain layer. Several surface defect structures presumably caused by the oxygen depletion are revealed. Among them, an one dimensional structural modulation with period of 1.5 nm alongbaxis is seen, which is suggested to be created by the ordering of the oxygen vacancies. The surfaces of Nd123 single crystals are proved to be highly clean and stable in air. Our results indicate that Nd123 single crystals are good materials for surface sensitive scientific researches and device applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121256

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The resistance of polycrystalline dopedLaMnO3materials has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries we have grown epitaxialLa0.7Sr0.3MnO3films on a series of bicrystal substrates with different misorientation angles and patterned the films into a Wheatstone bridge geometry. We show that the grain boundary resistance and its magnetic field dependence vary strongly with the misorientation angle. The temperature dependence of the grain boundary resistance is also presented. We have obtained resistance changes of over 3&percent; in fields of 2 mT at 300 K. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121257

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using numerical micromagnetics we have studied the ground state magnetization distribution of square planar ferromagnetic elements (“nanostructures”). As the element size is reduced from 250 to 2 nm at constant thickness (2–35 nm), we find that the magnetization distribution undergoes up tothreephase transitions involving as many as three different near single domain states. One of these phase transitions is analogous to the reorientation phase transition observed in continuous ultrathin magnetic films. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121258

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The magnetoelastic (MEL) stresses of single crystal Ho and Er thin films are measured at low temperatures and in applied magnetic fields up to 12 T by means of a capacitive cantilever technique, to determine the irreducible second-order basal plane MEL stressB&ggr;,2. For Ho, the data are well fit by the Callen and Callen law, givingB&ggr;,2=0.29 GPa at 0 K and 12 T, slightly larger than the bulk value, which suggest a negligible effect of the clamping onB&ggr;,2. For Er, the lack of saturation prevents the determination of the single-ion contribution toB&ggr;,2at 0 K. Nevertheless, its sign, which is negative, agrees with the theoretical crystal field prediction. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121259

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Co, Ni, Mn, Cr, and Cu substituted magnetites were prepared by the hydrothermal method at 300 °C, with concentrations ranging from 8.2&percent; to 12.5&percent;. Transmission electron microscopy determined the average particle diameter ⟨&Fgr;⟩ to be in the hundred of nm range and the morphological modifications induced by the various substitutions employed. Hysteresis loop measurements were performed to determine the coercive fieldHc,and saturation magnetic momentms.WhileHcdecreased with increasing ⟨&Fgr;⟩, the particle shape was found to play an important role in explaining the dependence ofmson ⟨&Fgr;⟩. Transmission Mo¨ssbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields. The room-temperature Mo¨ssbauer spectra were analyzed assuming a random distribution of substitutents using the binomial distribution from the ionic crystal point of view. Superparamagnetic particles were observed at room temperature in the case of Cu and Cr substituted magnetites. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121260

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The low energy electron absorption by ap(1×1)ordered oxygen overlayer on magnetized Fe(001) depends on the spin polarization of the primary beam. The peak value of the spin asymmetry is 12.5&percent; at 6 eV electron kinetic energy, where the percentage absorption is 65&percent;. The presence of the surface oxide prevents the system from contamination, so that an almost negligible asymmetry deterioration is observed after prolonged operation in vacuum. After exposure to atmosphere followed by heat-cleaning a peak value still larger than 7&percent; is achieved. These results suggest spin dependent current absorption fromFe(001)-p(1×1)Oas a very promising candidate for an efficient and extremely stable electron polarization analyzer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121261

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In order to study the effect of applied magnetic field on the superparamagnetic relaxation behavior of small Co particles, magnetization measurements were carried out on as-prepared and annealed granular samples ofCo20Ag80andCo25Ag75.Values of the superparamagnetic blocking temperatureTB−were obtained from the characteristic peak in the zero-field-cooled magnetization. Consistent with existing models, it was found that the initial decrease ofTB−with applied magnetic field is quadratic. An estimate of the magnetic anisotropy “energy density”Kuyielded a value which is two orders of magnitude greater than the value for bulk cobalt. The results reported here underscore the importance of considering the effect of superparamagnetic relaxation on the performance of nanostructured magnetic materials. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121262

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The thermoelectric properties (resistivity and thermopower) of single crystals of the low dimensional pentatelluride materials,HfTe5 andZrTe5,have been measured as a function of temperature from 10K<T<320K. The effect of small amounts of Ti substitutional doping(M1−xTixTe5,whereM=Hf, Zr) on the thermoelectric properties is reported here. A resistive transition occurs in the pentatellurides, as evidenced by a peak in the resistivity,TP≈80K forHfTe5andTP≈145K forZrTe5.Both parent materials exhibit a large positive (p-type) thermopower near room temperature which undergoes a change to negative (n-type) below the peak temperature. The thermal conductivity is relatively low (≈5 W/m K) for theMTe5materials. The Ti substitution affects the electronic properties strongly, producing a substantial shift in the peak temperature while the large values of thermopower remain essentially unaffected. These results warrant further investigation of these materials as candidates for low temperature thermoelectric applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121406

出版商:AIP    

年代:1998

数据来源: AIP