摘要:

The switching field interval,&Dgr;Hs,of Ni–Fe–Co-based thin films and spin-valve layered structures, sputter-deposited on a Ta-buffer layer, was studied. The switching field interval is the field range in which the magnetization reversal of a ferromagnetic layer takes place. In thin films,&Dgr;Hsis determined by the uniaxial anisotropy, induced by growth in a magnetic field. This anisotropy increases with the ferromagnetic layer thickness and saturates at a thickness of 10–25 nm. It also depends on the alloy composition as well as on the choice of the adjacent layers. In exchange-biased spin valves, an additional contribution to&Dgr;Hswas observed, which increases monotonically with increasing interlayer coupling. We explain this in terms of the effect on the magnetization reversal of the sensitive layer due to a simultaneous small, but temporary, magnetization rotation in the exchange-biased layer and lateral variations of the interlayer coupling. In addition, the effect of biquadratic coupling on&Dgr;Hsis discussed. Finally, the thermal stability of&Dgr;Hsis investigated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365660

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties ofGd2Co17−xGaxcompounds(x=0,1, 2, 3, 4, 5, 6, 7, and 8). Crystal-structure studies indicate that all samples are single phase with the rhombohedralTh2Zn17-type structure except for the samples withx=7and 8, which contain a small amount of Co. The Ga substitution for Co inGd2Co17compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization. The Curie temperatureTCis found to decrease monotonically from 1210 K forx=0to 30 K forx=8.The compensation points are observed for theGd2Co17−xGaxsamples withx=5and 6. The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K forx=5and 6, respectively. It is noteworthy that the substitution of Ga for Co in theGd2Co17compounds has a remarkable influence on the magnetocrystalline anisotropy. XRD studies on magnetic-field orientedGd2Co17−xGaxpowders show that the sample withx=0exhibits an easy-plane anisotropy, while the samples withx⩾1exhibit an easyc-axis anisotropy at room temperature. The change of the easy magnetization direction ofGd2Co17−xGaxcompounds from a basal plane tocaxis indicates that the substitution of Ga for Co leads to the decrease of the planar anisotropy of the Co sublattice. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365757

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article, we report about complexes in silicon investigated by electron paramagnetic resonance (EPR). In silicon doped with C and Pt we detected two different complexes: cr-1Pt (cr: carbon-related, 1Pt: one Pt atom) and cr-3Pt. The complexes have similar EPR properties. They show a trigonal symmetry with effectiveg-valuesgeff,⊥=2g⊥≈4andgeff,‖=g‖≈2(g⊥,g‖trueg-values). Theg-values can be explained by a spin Hamiltonian with large fine-structure energy (electron spinS=3/2)and smaller Zeeman interaction. The participation of platinum in the complexes is proved by the hyperfine interaction. From experiments with varying carbon concentration we conclude that the complexes contain carbon. Atomistic models based on the Watkins vacancy-model for substitutional Pt were developed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365661

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical properties of thin silicon dioxide films have been investigated for samples that suffered from the Fowler–Nordheim (F–N) stress and subsequent annealing. The time-dependent dielectric breakdown (TDDB) lifetime for samples after annealing>400 °Cwas found to be longer than that without anneal; about 60&percent; of the amount of damage responsible for the lifetime was annealed out at a temperature of typically 800 °C for 30 min. On the other hand, capacitance–voltage(C–V)measurements indicated that trapped charges were almost annealed out even at a temperature of 300 °C for 30 min. Moreover, the reinjection of F–N current showed that the trapping sites of holes and electrons which are electrically neutral remained after the annealing of trapped charges at temperatures>300 °C.It follows that the recovery of TDDB lifetime presently observed through annealing at temperatures>400 °Cwas caused by the anneal of neutral trapping sites created by F–N stresses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365662

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ferroelectric Nd-modified lead-zirconate-titanate (PZT) thin films were fabricated as capacitor structures with platinum electrodes using pulsed laser ablation deposition. Single-crystal MgO (100) and thermally oxidized Si (100) were used as substrates. The ablation processes were carried out at room temperature in a pressure of4×10−5 mbarin a vacuum chamber. A pulsed XeCl excimer laser with the wavelength of 308 nm was used for the ablation of both platinum andPb0.97Nd0.02(Zr0.55Ti0.45)O3targets. For the PZT films with thicknesses between 300 and 600 nm, a laser-beam fluence of1.0 J/cm2was used. Amorphous PZT films were postannealed at 675 and 650 °C in the cases of MgO and silicon substrates, respectively. The dielectric constant and the loss angle were measured at room temperature as a function of the film thickness. On the MgO substrate the dielectric constant of the films increased from 400 to 600 with the increasing film thickness, while in the films on the silicon substrate the dielectric constant was typically 140. The Curie temperature of the films was about 360 °C. The remanent polarization was about18 &mgr;C/cm2in the films deposited on MgO, but in the films on the silicon substrate the polarization values were much lower. The conductivity of the PZT thin films was studied as a function of temperature and electric field. Low-field resistivities of the order of1012 &OHgr; cmwere measured at room temperature. Macroscopic mechanical stresses in the PZT films were measured by the x-ray diffraction method. The films on the MgO substrate were in a compressive stress, while in the films on the silicon substrate a higher tensile stress was found. The dielectric constant was found to decrease and the coercive field to increase with the increasing mechanical stress. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365663

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The temperature dependence of the transient current in ferroelectricPb(Zr0.53Ti0.47)O3(PZT) thin film capacitors is studied by examining the current density versus time(J-t)characteristics in the temperature range from room temperature to 140 °C. The transient current consists of two components, the conduction current and the polarization current. The conduction current is related to traps inside the films. The trapped holes cause an increase of the local electric field and hence the conduction current. The polarization current decreases and saturates as time increases. The dependence of the transient current on temperature therefore relies on the relative magnitudes of the two components. The transient current of PZT at room temperature is found to be dominated by trap-related conduction current at field higher than 83 kV/cm and by polarization current at field lower than 83 kV/cm. The increase of temperature enhances the emission rate of captured holes and the conduction current component decreases. The discharging current in the PZT capacitor is found to follow the tunneling front model in the temperature range below 100 °C, whereas a different model is required above 100 °C. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365664

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin films of(Ba,Sr)TiO3onPt/SiO2/Sisubstrates were deposited using rf magnetron sputtering at various substrate temperatures andO2/(Ar+O2)mixing ratios (OMR). The crystallinity of the films improved significantly as the OMR increased. The dielectric constant increased with increasing OMR and reached a maximum value at 50&percent; OMR. The leakage current density decreased with increasing oxygen flow, but had a minimum value at 40&percent; OMR. The results for the dielectric constant and the leakage current were interpreted in terms of polarization effect and loss theory. The film deposited at 450 °C and 50&percent; OMR exhibited good surface morphology and had a dielectric constant of 375, a tangent loss of 0.074 at 100 kHz, a leakage current density of7.35×10−9 A/cm2at an electric field of 100 kV/cm with a delay time of 30 s, and a charge storage density of49 fC/&mgr;m2at an applied field of 150 kV/cm. The 10 yr lifetime of time-dependent dielectric breakdown studies indicate that a 50&percent; OMR sample has a longer lifetime than the 0&percent; OMR sample. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365665

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Piezoelectric activity in cyclohexane-treated polyvinyl chloride films has been found to increase when processed under simultaneously stretched and corona poled (SSCP) conditions. The piezoelectric coefficientd31=7.2±1.1pC/N was obtained in these films under optimum poling conditions. The main contributor to the improved piezoelectricity has been the increased dipolar polarization. Crystallinity and compliance have contributed marginally to the former. Thermally stimulated current (TSC) experiments show that maximum oriented dipole density has been achieved during the SSCP. Dipolar polarization≈10−2 C/m2has been obtained. The TSC and the shrinkage effect involving molecular rotation and/or chain motion are closely related. An application of the extended Mopsik and Broadhurst theory shows that 56&percent; of the measuredd31is due to the dimensional effect and 44&percent; due to the local field effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365666

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of photon recycling are examined in a general, fully numerical, two-dimensional model accounting for the detailed geometry of the device and the spectral content of the recombined excess carriers. The primary component of this model is a three-dimensional ray tracing algorithm which encompasses effects such as wavelength dependent absorption and index of refraction, the angular dependence of transmissivity between layers in a heterostructure device, and multiple reflections within a device. This ray tracing preprocessing step is used to map all of the possible trajectories and absorption of various wavelengths of emitted light from each originating node within the device. These data are integrated into a macroscopic device simulator to determine the spatial and temporal location of the reabsorbed radiation within the geometry of the device. By incorporating the ray tracer results with the total quantity and spectral content of recombined carriers at each node within the simulation, the recycled generation rate can be obtained. To demonstrate the use of this model, the effects of photon recycling on the carrier lifetime in an InP/InGaAs double heterostructure photodiode are presented. Good agreement between the experimentally measured lifetime and that predicted using photon recycling is obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365622

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A spontaneous Raman scattering from the surface phonon modes (SPMs) of amorphous silica(SiO2)nanoparticles which is small compared with the excitation wavelength (514.5 nm) and aggregated in micron size clusters (globules) is utilized to determine the shape of particles. The excitation dynamics for these modes were studied for silica samples pretreated at different temperatures (30–1000 °C). The SPMs are located between Raman peaks corresponding to the bulk traverse-optical (TO) and longitudinal-optical (LO) asymmetrical and bending phonon modes. An anomalously large TO-LO splitting (∼185cm−1) of bending modes was observed. The shape examination was based on the fact that three depolarization factors are equal in value for spherical nanoparticles, but they are different for an elliptical one. According to this, one can observe one or three SPMs, respectively. The position of corresponding Raman peaks allows one to determine the depolarization factors and subsequently the shape of nanoparticles. The single SPM is located between Raman peaks corresponding to the TO and LO asymmetrical phonon modes and can be attributed to small spherical particles. Six different SPMs, which are located between Raman peaks corresponding to the TO and LO bending phonon modes, were observed. These modes can be assigned to elliptical nanoparticles in two surrounding mediums of different effective dielectric constants. The intensity of these SPMs is decreased drastically by heat treatment at a temperature around 950 °C, suggesting that aggregates of nanoparticles form the bulk &agr;-quartz structure. The bulk structure formation from small silica particles was supported by thermogravimetric measurements. The values of the fraction of the total sample volume occupied by particles were calculated theoretically. A good agreement with the theory was obtained by assuming the anomalously large TO-LO splitting of bending phonon modes in nanoparticles of the amorphous silica. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365667

出版商:AIP    

年代:1997

数据来源: AIP