摘要:

Surface and ultrathin‐film magnetocrystalline anisotropy in epitaxial fcc Fe thin films grown on room‐temperature Cu(100) single crystals has been investigated,insitu, by the combined surface magneto‐optical Kerr effects (SMOKE). In polar, longitudinal, and transverse Kerr effects, the direction of the applied magnetic field must be distinguished from the direction of magnetization during the switching process. For arbitrary orientations of the magnetization and field axis relative to the optical scattering plane, any of the three Kerr effects may contribute to the detected signal. A general expression for the normalized light intensity sensed by a photodiode detector, involving all three combined Kerr effects, is obtained both in the ultrathin‐film limit and for bulk, at general oblique incidence angles and with different orientations of the polarizer, modulator, and analyzer. This expression is used to interpret the results of fcc Fe/Cu(100) SMOKE measurements. For films grown at room temperature, polar and longitudinal Kerr‐effect magnetization loops show that the easy axis of magnetization rotates from the (canted) out‐of‐plane direction to the in‐plane direction at a thickness of about 4.7 monolayers. Transverse Kerr‐effect measurements indicate that the in‐plane easy axes are biaxial.

ISSN:0021-8979    

DOI:10.1063/1.355081

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Sm2Fe17N2.9compound powders were prepared from parent alloys of Sm2Fe17which were made by both the arc‐melting and rapid solidification processes. The cast Sm2Fe17contained mixed phases of SmFe3and &agr;‐Fe, and correspondingly formed less Sm2Fe17Nxwith a rather large amount of residual &agr;‐Fe after nitrogenation. The melt‐spun Sm2Fe17compound, however, was single phase and exhibited a negligible amount of residual &agr;‐Fe after nitrogenation. The residual amount of free iron was found to increase as a function of milling time and impede the development of promising permanent magnetic properties. The melt‐spun Sm2Fe17Nxcompound powders exhibited a coercivity valueiHcof 5 kOe, which is double that of the as‐cast Sm2Fe17Nxpowders and a high remanence,Br=60 emu/g. The average magnetic moment of Fe atoms in the crystal is estimated to be 2.29 &mgr;Band the Fe atom in the 6csite shows the highest magnetic moment of 2.65 &mgr;B. The expansion in thec‐axial direction of the nitrogenated crystal was found to be mainly due to extension of Sm(6c)‐Fe(6c) and Fe(18f)‐Fe(18f) distances.

ISSN:0021-8979    

DOI:10.1063/1.355082

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Based on the universal additivity law of the interference of light the following was achieved. (i) An analytic representation between the eigenvalue of the Kerr rotation angle &thgr;0kand the enhanced &thgr;kfor a double‐layered film, &thgr;k=en1&thgr;0k, was obtained theoretically, whereeis the enhancement factor andn1is the refractive index of the dielectric medium. (ii) An analytic representation between &thgr;kand &thgr;0k(&thgr;k=e013e123n2&thgr;0k) of the trilayered film [bilayered transparent media and monolayered magneto‐optical (MO) medium], was also obtained, wheree013ande123are the enhancement factors: The calculated &thgr;kvalue is in good agreement with experimental results fore=1. In general, the theoretical calculation shows that &thgr;kis related to the thickness of the transparent media. Thus, if one wants to get an optimum value for &thgr;k, the thickness of the first transparent film layer (such as a glass substrate) must be selected carefully. It also shows that if the variation of the thickness of the glass substrate is 5 nm, &thgr;kcould vary by 0.1° for MnBiCe films. (iii) The relation connecting &thgr;kwith &thgr;0k1and &thgr;0k2for bilayered MO films has been theoretically studied, where &thgr;0k1and &thgr;0k2are the eigenvalues of the Kerr rotation angle of MO materials 1 and 2, respectively. Finally, &thgr;kfor a Fe/Co film was calculated.

ISSN:0021-8979    

DOI:10.1063/1.355083

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Kerr spectra and magnetic properties for multilayers of ultrathin Co and Cu/Au composite layers were systematically investigated. A Kerr enhancement was observed for the multilayers. The peak position of Kerr rotation shifts from the Cu plasma edge (560 nm) to the Au plasma edge (480 nm) by varying the constitution of Au/Cu/Au and Cu/Au/Cu parts. Magnetic anisotropies for the multilayers strongly depend on the constitution of Cu/Au composite layers. For [Cu(tA˚)/Au(25−2tA˚)/Cu(tA˚)/Co(8 A˚)]15multilayers, the easy axis changes from perpendicular to parallel along the film plane at a Cu layer thickness of around 2.5 A˚. The anisotropy for the [Au(tA˚)/Cu(25−2tA˚)/Au(tA˚)/Co(8 A˚)]15multilayer remains unchanged below a Au layer thickness of 3 A˚ and increases above that thickness. The change of easy axis is mainly due to the change of interface anisotropy.  

ISSN:0021-8979    

DOI:10.1063/1.355084

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Carbon was introduced by arc melting to RTiFe11, where R=Sm, Gd, Th, Dy, Ho, Er, and Y, and its effects on the crystallographic and magnetic properties of these compounds have been investigated by x‐ray and magnetic measurements. The experimental results show that the carbon atoms occupy 8isites in ThMn12structure. It is found that the substitution does not have an effect on the Curie temperature, but instead increases both saturation magnetization and magnetocrystalline anisotropy. The intrinsic magnetic properties of SmTiFe11are improved with the addition of the carbon atoms, indicating that SmTiFe11−xCxis a better candidate for permanent magnetic applications than SmTiFe11.

ISSN:0021-8979    

DOI:10.1063/1.355085

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Strontium titanate thin films were deposited by electron‐cyclotron‐resonance plasma‐assisted radio‐frequency magnetron sputtering. Electron‐cyclotron‐resonance plasma assistance was employed because of its ability to be used as a source of low‐energy bombardment by a high density of species that are highly activated. It was found that both the structure and composition improve with the application of microwave plasma during the deposition. Analysis of the capacitance‐voltage characteristics of metal‐insulator‐semiconductor devices revealed that the quality of the film/substrate interface is dependent on the pressure, atmosphere, and temperature of the deposition. Interfacial traps which give rise to charged surface states and silicon oxide formation have detrimental effects on films deposited on bare silicon substrates. Films on platinum‐coated silicon substrates show good dielectric properties. The small‐signal dielectric constant and dissipation factor at a frequency of 100 kHz were 170 and 0.033, respectively. For a 0.37‐&mgr;m‐thick film a charge storage density of 28 fC/&mgr;m2and a unit area capacitance of 3.7 fF/&mgr;m2were obtained at an applied electric field of 200 kV/cm.

ISSN:0021-8979    

DOI:10.1063/1.355086

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The space dependence of charge carriers trapped in &agr;‐quartz under electron‐beam bombardment is investigated using a Monte Carlo algorithm. The average energy of the electron after being detrapped from a trap site is first calculated by considering both the polar and nonpolar phonon scatterings. Later, the detrapping and trapping rates are also included in the model to obtain a stable trapped charge distribution, which is found to be dependent on the size as well as the temperature of the sample. Comparisons with experimental results of the size effect on the dielectric strength obtained from a scanning electron microscope are also made.

ISSN:0021-8979    

DOI:10.1063/1.355087

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Low temperature (∼5 K) photoluminescence spectroscopy was performed on undoped CdTe epilayers grown by molecular beam epitaxy on (211)B oriented bulk GaAs substrates at substrate temperatures ranging from 230 to 275 °C. The emission spectra from all samples studied contained evidence of the diffusion of gallium and arsenic atoms from the substrate. A broad, low amplitude emission band observed at 1.594 eV was related to the GaCddonor level in CdTe. Donor‐acceptor pair recombination observed at 1.51 eV was due to the substitutional GaCddonor and AsTeacceptor. The level of compensation in the CdTe layers was determined from the energy shift of the donor‐acceptor emission peak with excitation power, with the lowest degree of compensation observed in a sample grown at 230 °C. In addition, a bright emission peak was observed at 1.47 eV. This peak, which had been observed previously in homoepitaxial and heteroepitaxial growth of CdTe, was related to electron‐hole recombination of a structural defect in the CdTe/GaAs epilayers with an electronic binding energy of ∼130 meV.

ISSN:0021-8979    

DOI:10.1063/1.355088

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We theoretically calculate the electric field induced refractive change index for the ground to first excited state transition in the conduction band of asymmetrical quantum wells. We show that there is a significant change in stark shifts and the refractive index with asymmetry potential. Comparing the results for a square, graded, and step well, it is found that larger refractive index change can be achieved in a step well by a proper choice of the step potential.

ISSN:0021-8979    

DOI:10.1063/1.355089

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Infrared transmission spectra of silicon dioxide (SiO2) thin films (∼4500 A˚) prepared by plasma‐enhanced chemical‐vapor deposition have been quantitatively analyzed. The films were deposited at different substrate temperatures (30–450 °C) using tetraethoxysilane (TEOS)/He, TEOS/He/O2, and TEOS/O2gas mixtures in a parallel‐plate radio‐frequency reactor. The infrared transmission fits prove to be very accurate showing evidence of deconvolution into three separated Gaussian profiles to account for the asymmetric line‐shape feature of the infrared stretching peak between 950 and 1300 cm−1. The examination of the Fourier transform infrared spectroscopy spectra in the complete frequency range (400–4000 cm−1) andexsitux‐ray photoelectron spectroscopy spectra indicates that some extra structures originate from the incorporation of carbon and hydrogen impurities in the film. As the substrate deposition temperature is increased, impurities are gradually removed from the growing layer. Films deposited at high substrate temperatures reveal a better stoichiometry and present similar deconvolution bands regardless of the gas‐phase composition; the corresponding frequencies are shifted to lower energies compared to thermal oxides. In addition, the intensity of the first Gaussian profile, associated with the low‐energy asymmetry of the stretching peak, increases with the substrate deposition temperature while the intensity of the third Gaussian profile associated with the presence of the high‐energy peak shoulder decreases. The vibrational properties of the film seem to be strongly related to the deposition conditions.

ISSN:0021-8979    

DOI:10.1063/1.355090

出版商:AIP    

年代:1993

数据来源: AIP