摘要:

The first order anisotropy field strength of sintered orientated NdFeB samples is determined by transverse susceptibility measurement. It is shown that this method yields reliable data, even if the applied field is much smaller than the anisotropy field to be detected. Systematic and technical error sources are discussed on the basis of calculation results.  

ISSN:0021-8979    

DOI:10.1063/1.353414

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This article reports on the relations between the magnetic properties and crystal structure of Co‐Fe‐Al‐N films prepared by rf magnetron sputtering in a mixed Ar and N2gas atmosphere. Slightly substrate‐biased 4 at. % Al films showed a low coercivity of less than 80 A/m, a low magnetostriction of less than 1×10−6, and a high saturation magnetic flux density of 1.7 T. These features were maintained after annealing at up to more than 500 °C. The lowHcwas related to the crystal structure of a face‐centered‐cubic phase with an about 10‐nm grain size. No detectable AlN was observed by an x‐ray diffractometry even after annealing. However, the lattice constant after annealing was nearly equal to that of a Co‐Fe alloy and the Al content increased with the increase in sputtering N2‐gas content, suggesting the binding of Al and N atoms.

ISSN:0021-8979    

DOI:10.1063/1.353415

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Ternary compounds (Pr,Nd,Sm)Mn6Sn6have been synthesized by argon arc melting starting from the pure elements. All compounds were found to be isotypic with HoFe6Sn6(space groupImmm‐D2h25, no. 71;Z=6). The HoFe6Sn6type is a stacking variant composed of slabs of the HfFe6Ge6type and of the ScFe6Ga6type. The compounds order ferrimagnetically slightly above room temperature exhibiting a strong magnetocrystalline anisotropy. The119Sn Mo¨ssbauer spectra at 15 and 293 K were fitted with five magnetic sextets, with hyperfine fields ranging from 12 to 32 T at 15 K.

ISSN:0021-8979    

DOI:10.1063/1.353416

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The &OHgr;tintensity parameters (t=2,4,6) of Er3+ions in several oxide glasses and the isomer shift (IS) of151Eu Mo¨ssbauer spectra in glasses of the same composition were determined. Among these &OHgr;t’s, the &OHgr;6parameter was found to have a good relation with IS; &OHgr;6decreases with an increase of IS which reflects the 6selectron density of rare‐earth ions. From the theoretical expression of &OHgr;t, &OHgr;6is considered to be more affected by the overlap integrals of the 4fand 5dorbitals than &OHgr;2and &OHgr;4, and to increase with an increase of these overlap integrals. These overlap integrals are supposed to decrease when the 6selectron density is larger, since the 6selectron density shields the 5delectron orbital.

ISSN:0021-8979    

DOI:10.1063/1.353417

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report the observation of self‐defocusing in GaP with nanosecond, 532‐nm laser pulses. An electronic refractive nonlinearity (−1×10−21cm3) has been obtained. We also present a band‐filling theory for the band‐gap resonant nonlinear refraction in indirect–band‐gap semiconductors. A comparison shows that the theory is in good agreement with the experimental result.

ISSN:0021-8979    

DOI:10.1063/1.353418

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Criteria are developed for selecting a barrier materialXYsuch that Si/XYsuperlattices should emit light from their Si quantum wells. GaAs is such a material for [001] superlattices. In many such superlattices, substitutional N on a Si site will be a shallow donor, not a deep trap.

ISSN:0021-8979    

DOI:10.1063/1.353419

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A scheme for enhancing the refractive index change &Dgr;nin the wavelength region longer than that for ann=1 heavy‐hole exciton peak, where the absorption coefficient &agr; is small, is proposed and three‐step GaAs/AlGaAs quantum wells (QWs) are numerically analyzed as an example. The basis of this scheme is that an electric‐field‐dependent oscillator strength can be controlled by designing a QW structure which yields either positive or negative absorption change, &Dgr;&agr; at all wavelengths, resulting in an increase in the &Dgr;nin the longer wavelength region and a reduction in the operating electric field. The numerical analysis predicts that the electric field for the three‐step QW that yields a &Dgr;nof ∼10−2is as small as 5–15 kV/cm which is about one order of magnitude smaller than that for a conventional square‐potential QW. In addition, the &Dgr;nand the figure‐of‐merit, which is defined as &Dgr;n/&agr;, are larger than those for the conventional QW in the longer wavelength region.

ISSN:0021-8979    

DOI:10.1063/1.353420

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The orientational decay of chemically and thermally stable high‐temperature chromophores doped into thin films made from polyimides and a variety of other polymeric hosts has been investigated. The chromophores are aligned using electric field poling and second‐harmonic generation (SHG) is used to probe the decay of the electric field poling induced alignment. The decay rate of the SHG signal from films poled using both a corona discharge and side‐by‐side in‐plane electrodes was measured. When electrodes are chosen so that the effects of charge injection are minimized, little difference has been observed between the orientational decays from films poled using the two methods for either an amorphous preimidized polyimide host or a highly anisotropic film poled during imidization. The films imidized during poling showed significant orientational stability at 250 °C for over 15 h after a fast initial partial decay. In addition, the decay of the SHG signal was measured as a function of temperature below the glass transition in a wide variety of different polymer host systems. The temperature dependence of the decay was found to be non‐Arrhenius, but could be strongly correlated with the glass transition temperature of the guest‐host system using an empirical relationship similar to the Williams–Landel–Ferry or Vogel–Tamann–Fulcher equation.  

ISSN:0021-8979    

DOI:10.1063/1.353421

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have developed an experimental technique for accurately determining energy‐band offsets in semiconductor quantum wells (QW) based on the fact that the magnitude of the ground‐state light‐hole (LH) energy is more sensitive to the depth of the valence‐band well than is the ground‐state heavy‐hole (HH) energy. In a lattice‐matched, unstrained QW system, this behavior causes the energy difference between the LH and HH excitons to go through a maximum as the well width,Lz, increases from zero. Calculations show that the position, and more importantly, the magnitude of this maximum is a sensitive function of the valence‐band offset,Qv, the parameter which determines the depth of the valence‐band well. By usingQv, or alternativelyQc=1−Qv, as an adjustable parameter and fitting experimentally measured LH‐HH splittings as a function ofLz, an accurate determination of band offsets can be derived. However, we further reduce the experimental uncertainty by plotting LH−HH as a function of HH energy (which is, itself, a function ofLz) rather thanLz, since then all of the relevant data values can be precisely determined from absorption spectroscopy alone. Using this technique, we have derived the conduction‐band offsets for several material systems, including lattice‐mismatched systems and, where a consensus has developed, have obtained values in good agreement with other determinations.

ISSN:0021-8979    

DOI:10.1063/1.353422

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Using Fourier transform infrared spectroscopy, we investigated hydrogenated amorphous silicon‐carbide (a‐Si1−xCx:H) films, deposited in a standard rf glow discharge. Different gas mixtures in combination with silane (SiH4) were used, namely methane (CH4), disilylmethane, trisilylmethane, and tetrasilylmethane. Methane‐based and silylmethane (SM)‐baseda‐Si1−xCx:H films yield two different classes of material. SM‐based alloys contain more SiC groups and more CH groups, but less CH3groups than methane‐based material. In SM‐based material, hydrogen is mainly bonded to silicon atoms, whereas in CH4‐based material hydrogen is chiefly bonded to carbon.  

ISSN:0021-8979    

DOI:10.1063/1.353400

出版商:AIP    

年代:1993

数据来源: AIP