摘要:

When bismuth-substituted iron garnet (RBi)IG single crystals grown from liquid-phase-epitaxy (LPE) are magnetized, the magnetic domain structure gradually evolves. However the domain-wall nucleation that occurs during the demagnetization is not yet understood clearly. This phenomenon is important, because the working of some optical devices that utilize (RBi)IG single crystals depends directly on the formation of domains of opposite direction. In this paper, the authors present a theoretical description of domain-wall nucleation in LPE-grown (RBi)IG single crystals. It was found that the nucleation field is determined by the strength of the microscopic domain-wall which is fixed on the surface of the crystal. Furthermore, the nucleation field is modified by the addition of a magnetic field.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366056

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Off-axis electron holography at the nanometer level has been used to investigate the magnetic microstructure of thin epitaxialFexPt1−x(x∼0.5)ordered alloy films. High-resolution electron microscopy in cross section showed high quality epitaxial growth but also revealed some widely spaced regions with structural defects. Lorentz microscopy and off-axis electron holography in field-free conditions established conclusively that similar defective areas were associated with local perturbations of the in-plane magnetic field within the thin films. Further holographic observations with the FePt[001] axis parallel to the film normal revealed variations in phase shifts in the vacuum outside the sample which indicated flux leakage along the film normal. Overall, the results demonstrate that off-axis electron holography is a highly useful technique for mapping local variations of the in-plane magnetic structure associated with defective thin films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366057

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetizing, demagnetizing, and remanent magnetization curves for[Co(12 Å)/Ag(60 Å)]×15multilayered/granular films thermally treated have been measured. The changes of the giant magnetoresistance and the interaction effects have been explained as a result of the structural, morphological, and magnetic evolution of the samples as a function of the thermal treatment. It has been inferred that for samples annealed at temperatures lower than 360 °C, the changes of the giant magnetoresistance come from the misalignment of the magnetic moments of the Co particles formed during annealing. A strong correlation between the giant magnetoresistance and the magnetic interaction effects has been found for samples annealed at temperatures higher than 360 °C: the giant magnetoresistance is degraded as the demagnetizing interparticle interactions are increased. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366058

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nuclear spin-lattice relaxations ofBe9andAl27in an alexandrite(BeAl2−xCrxO4,x=0.02) single crystal have been investigated in the temperature range 140 K–400 K. The paramagnetic impurity effect on the relaxation is negligible for both nuclei. The relaxation of theBe9nuclear spins is found single exponential in time when the whole resonance lines are uniformly excited. When only the central resonance line is excited forAl27, the relaxation is well fitted with a linear combination of three exponential functions given by Simmons &etal; [Phys. Rev.127, 1168 (1962)]. Since the spin-lattice relaxation rate is proportional to the square of temperature for both nuclei, the dominant relaxation mechanism in this temperature range can be inferred as the Raman process. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365767

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Unlike the photographically important silver halides, large NaCl single crystals can be grown from solution. In such NaCl crystals, with doping comparable to practical AgCl and AgBr microcrystals, three stable Rh centers were detected and studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). The primary center was identified as a nonlocally compensated[RhCl6]4−complex, at variance with earlier reported EPR work. By lack of sufficient EPR and/or ENDOR evidence, the identity of the two other Rh related centers with orthorhombic and isotropic symmetry respectively, remains rather speculative. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366059

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this work sinusoidal diffraction gratings with a range of pitches and amplitudes are used to align nematic liquid-crystal layers in a twisted homogeneous configuration. The grating profiles are accurately characterized using optical surface plasmon polariton spectroscopy, which then allows a calculation of the anchoring energy as predicted by the simple Berreman expression. The experimental Rapini–Papoular anchoring energy is also obtained by a measurement of the director twist away from the alignment direction (easy axis) at room temperature. A linear relationship is found between the two anchoring energies, except when it falls below4×10−7 J m−2.Noticeably, the correlation between the two theories is not unity, if room-temperature elastic constants are used in the calculation. This apparent inconsistency is explained if the effect of surface memory on the system is considered. Indeed, if elastic constants, corresponding to a higher temperature at which surface memory effects are absent, are used in the Berreman expression, good agreement between the predicted and experimentally measured energies is found. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366060

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For the conditioned samples, there is a good agreement between the experimental results and the analytical expression of the current, particularly in the region where it reaches a maximum, and so relevant values for the characteristic parameters of the peak are determined. The time interval of the short circuiting of the sample, at room temperature, before the TSDC measurement, strongly influences the initial rise of the current and consequently the parameters of the peak. A possible redistribution of the internal field arising from the injected charge, the heterocharge, and the existing charge in the sample as received, has been put forward to account for the experimental evidences. The conclusion is that the current is mainly determined by the space-charge released from the traps that are likely continuously distributed in energy. For the stated polarization conditions, the charge is released from the shallow traps with an activation energy in the range 0.23–0.32 eV and a concentration of∼1018/m3.The dipolar charge is of little importance. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366061

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The temperature- and field-dependent permittivities of fiber-texturedBa0.7Sr0.3TiO3thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness. These films display a nonlinear dielectric response under conditions representative of those encountered in dynamic random access memories or other integrated capacitor applications. This behavior has the exact form expected for a classical nonlinear, nonhysteretic dielectric, as described in terms of a power series expansion of the free energy in the polarization as in the Landau–Ginzburg–Devonshire approach. Curie–Weiss-like behavior is exhibited above the bulk Curie point(∼300 K),although the ferroelectric phase transition appears frustrated. Small-signal capacitance measurements of films with different thicknesses (24–160 nm) indicate that only the first term in the power series expansion varies significantly with film thickness or temperature. Possible origins for this thickness dependence are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366062

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A domain model consistent with the measured capacitance–voltage(CV)characteristics of lead zirconate titanate (PZT) capacitors is proposed. Two variants of this model are presented and compared with experimentally measuredCVdata. The basic model is developed adopting a macroscopic electric field that is spatially uniform through the depth of the film. Then, this model is generalized to allow a variation of the electric field with depth and to include a physically reasonable, position-dependent domain structure. Specifically, the spatial variation of the electric field is related to dopant–ion charges. As a result of the interaction between the domain properties and the electrical doping, a position dependent permittivity is induced, and the electrical properties of the capacitors are affected. Finally, computer simulations to fit the measuredCVcharacteristics are performed to help understand the extent of the coupling between the domain properties and the electrical doping. It is found that there is a minimum doping level below which the doping does not affect theCVcharacteristic. A method for determining this minimum doping level from theCVcurve is presented. The analysis of observedCVdata demonstrates that niobium doping is responsible for partially compensating thep-type nature of PZT thin films. For the films measured here, the minimum noticeable doping level is about1018 cm−3.It is also found that niobium doping slows the growth rate of polarization as the electric field increases, and has a tendency to increase the coercive field. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365764

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this paper, the extraction of doping profiles in ferroelectric thin-film capacitors using ferroelectric capacitance–voltage(CV)measurements is studied. For a ferroelectric field-dependent permittivity model, the doping profile relation to measuredCVcurves for ferroelectric thin-film capacitors is found to be analogous to the well-known result of metal–semiconductor Schottky junctions with an easily determined effective dielectric constant. Computer simulation shows the electrical doping concentration of ferroelectric thin-film capacitors can be profiled accurately with the proposed model. Limitations of the model are investigated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365766

出版商:AIP    

年代:1997

数据来源: AIP