摘要:

The interface states betweenn-type Si and amorphous carbon films rich insp3bonds grown by rf magnetron sputtering at room temperature have been examined. The investigation aimed to examine the effects of the low substrate temperature and the absence of hydrogen during the growth process on the density of interface states. Thus, comparing the values of the interface states to those reported for devices grown by other techniques, the best possible interface required for electronic applications is suggested. The conductance technique was used to measure the density of the interface states. This method revealed a value of the traps for then-Si(100)-carbon interface of the order of1010 cm−2 eV−1,nearly one order of magnitude lower than any other previously reported for the same configuration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366402

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

StoichiometricNb3Snfilms on sapphire were prepared with a tin vapor diffusion process from sputtered Nb precursors. The superconductive properties of the precursor and the converted films were measured at 1 kHz and 87 GHz. The nanocrystalline Nb films yieldedTc=7.8–9.3 K,&Dgr;Tc=0.05–0.30 K,Jc(4.2 K)=0.8–2.8 MA/cm2,and&rgr;(Tc)=1–35 &mgr;&OHgr; cm,indicating a high sensitivity to granularity and impurities. In contrast, the 0.5–3.0 &mgr;m thick and large-grainedNb3Snfilms showed reproduciblyTc=18.0 K,&Dgr;Tc=0.1 K,Jc(4.2 K)=5–6.5 MA/cm2,and&rgr;(Tc)=7.7–9.1 &mgr;&OHgr; cm.A reduced energy gap&Dgr;/kTc=1.8–2.2and a penetration depth&lgr;0(T=0 K)=65–80 nmwere deduced from the surface impedance measurements. The residual surface resistance dropped below the sensitivity limit of 0.3 m&OHgr;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366372

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on a new experimental approach to the size estimation of the hot spot induced by ionizing particles in a Josephson tunnel junction. Here, in contrast to the case of a superconducting strip, it is possible to investigate the hot spot dynamics in absence of effects due to the heating induced by the bias current. The reported experiment is based on the motion of Abrikosov vortices, trapped in the thin films constituting the junction electrodes, under 5.6 MeV &agr;-particle irradiation. The fast time evolution of a hot spot, combined with the presence of Abrikosov vortices, produces a change of the static magnetic field in the junction area and thus a change of the critical current value,Ic.Measurements ofIcduring the &agr;-particle irradiation and in presence of trapped Abrikosov vortices allow to determine the rate of appearance of thoseIcchanges. The behavior of the average appearance rate as function of the Abrikosov vortices density provides a direct determination of the maximum hot spot area. The experiment is performed on a high qualityNb/Al–AlOx/Nbjunction of circular geometry and with “small” dimensions with respect to the Josephson penetration depth. A value of4.7±1.2 &mgr;m2is found for the maximum hot spot area. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366373

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In order to develop superconducting thin films or multilayer structures suitable for Abrikosov vortex flux flow transistors, we propose a model to describe the current–voltage characteristics measured on microbridges operating in the flux creep regime and we show how the effective superconducting thickness of the samples, as well as the pinning potential range, the maximum velocity, the pinning energy, and the depinning current of the vortices can be determined. This model is applied to microbridges with structures containing one or severalYBa2Cu3O7−&dgr;layers which were deposited either onLaAlO3or onSrTiO3substrates. The results demonstrate that mostYBa2Cu3O7−&dgr;microbridges exhibit very similar properties and are not suitable for flux flow devices. However, bilayer structures comprised of aYBa2Cu3O7−&dgr;film and a conductive capping layer display interesting properties. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366374

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Perpendicular magnetic anisotropy of Fe/Tb multilayers was investigated using Mo¨ssbauer effect spectroscopy. Twenty-four multilayered Fe/Tb samples were prepared by planar magnetron sputtering. Results of Mo¨ssbauer effect measurements show that Fe/Tb multilayers display perpendicular magnetic anisotropy if the Tb layer thickness is less than 12 Å, and display in-plane anisotropy if the Tb layer thickness is more than 12 Å. Results indicate that the interface between Tb and Fe layers is the cause of the perpendicular anisotropy. Results also suggest that this perpendicular anisotropy is not induced due to the growth processes or the stress at the interface between the sample and the substrate. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366375

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of order–disorder structural transition on the magnetic, magneto-optical, and optical properties of nearly equiatomic FeAl alloy films was investigated. The disordered state in FeAl alloy films was obtained by means of vapor quenching deposition onto glass substrates cooled by liquid nitrogen. The experimental study of the magneto-optical and optical properties of ordered and disordered FeAl alloy films was carried out in the 0.5–5.0 eV energy range at room temperature. The influence of the order–disorder structural transition on magnetic, magneto-optical, optical properties is discussed by using the results of first-principle calculations of the electronic structure and by the structural defect approach. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366376

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The magnetic permeability and giant magnetoimpedance effect ofFe73.5Cu1Mo3Si13.5B9alloy ribbons in different annealed states have been measured as functions of the external magnetic field and the ac driving current frequency. It is found that the giant magnetoimpedance effect in the magnetic-field annealed state is larger than that in the nonfield annealed state. In the field annealed state, the easy magnetization direction is along the driving current as well as the external magnetic field. This leads to significant change of the permeability at high frequencies, and consequently the magnetoimpedance is enhanced in this state. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366377

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Sm2Fe15.5Si1.5C1.5samples with a rhombohedralTh2Zn17-type structure have been prepared by high frequency induction melting. The crystallization, crystal structure, and magnetic properties of melt-spun and annealed ribbons have been studied by means of x-ray diffraction, scanning electron microscopy, differential thermal analysis, and magnetic measurements. The results show that the as-spun ribbons consist mainly of an amorphous phase, and that they crystallize in two steps. Upon annealing at 660 °C the ribbons form a metastable phase of theTbCu7-type and an &agr;-Fe phase. Upon further annealing above 750 °C the metastable phase transforms to a 2:17-type phase coexisting with &agr;-Fe. A saturation magnetization of up to 108 emu/g with a coercivity of up to 3.5 kOe is obtained in the ribbon annealed at 660 °C for 30 min. However, the reduced remanence of the ribbon&sgr;r/&sgr;sis only 0.6 and its hysteresis loop exhibits two independent magnetic components. Additionally, the grain size of the ribbons obtained by annealing at or above 660 °C for 30 min is much larger than the single domain size. Thus, it appears that there is no significant exchange coupling between the hard and soft magnetic phases of the ribbons. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366378

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We propose a new method for analyzing the experimental results obtained from thermally stimulated depolarization current experiments on ionic conductors. This method is based on a model developed to explain polarization in these materials. The fundamental assumptions about the elementary mechanisms responsible for polarization is assumed to be due to the “free” volume created by thermal fluctuations occurring in solids near the equilibrium state. The consequence of these fluctuations is a statistical distribution of the relaxation times or energies, which can be evidenced by the thermal windowing technique, and then analyzed by relaxation map analysis. Applied to two typical ionic compounds, the method described in this work allows us to determine more realistic values of energy and&tgr;0, corresponding to the measured relaxation times. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366379

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dielectric and ac/dc transport properties of single crystals of yttrium iron garnet (Y3Fe5O12andY3Fe5O12:Si), and barium hexaferrite(BaFe12O19andBaFe12O1 9:Co,Ti) were investigated after irradiations with Xe and Pb ions in the GeV range. In the virginn-type samples (Y3Fe5O12:SiandBaFe12O19:Co,Ti), the strong dielectric relaxation below 100 kHz is found to correspond to a space-charge polarization at the blocking metal/insulator contacts yielding a nonohmic dc conductivity. The relaxation frequency decreases with increasing amorphization yield in relation to the decrease of the insulators bulk dc conductivity which becomes ohmic in the amorphous phases. The ac conductivity data of both crystalline and amorphousY3Fe5O12:Siabove 100 kHz and for100 K<T<300 Kexhibit two contributions: (i) that of carrier transport in a disordered or inhomogeneous medium varying as&ngr;s,withs≃0.8,(ii) and that of a two-site polaron hopping process of charge transfer betweenFe2+andFe3+with an activation energy of 0.29 eV forT>180 K.The dc conductivity data of crystallineY3Fe5O12:Sifor80 K<T<300 Kare discussed on the basis of a small polaron hopping conduction mechanism betweenFe2+andFe3+with an activation energy around 0.28 eV forT>125 K,in agreement with the activation energy around 0.28 eV of the space-charge dielectric relaxation frequency forT>180 K.All amorphous phases data are consistent with the picture of hopping conduction between gap states in a disordered medium with (i) an&ngr;sdependence for the ac conductivity above a critical frequency proportional to the dc conductivity, (ii) and anexp(−T−1/4)law for the dc conductivity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366403

出版商:AIP    

年代:1997

数据来源: AIP