摘要:

Metallic multilayer films consisting of ferromagnetic PtMnSb and antiferromagnetic CuMnSb were prepared by an rf sputtering method. From the x‐ray diffraction data, all the films were found to have a [111] texture of theC1b‐type Heusler structure. The magnetization measured in PtMnSb/CuMnSb multilayers was larger than that in a PtMnSb compound. The temperature dependence of magnetization shows a bend at about 50 K near the Ne´el temperature of CuMnSb. This bend is explained qualitatively by using a molecular field model and assuming a trapezoidal modulation of exchange interaction.

ISSN:0021-8979    

DOI:10.1063/1.345268

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Starting from a Hamiltonian based on the random magnetic anisotropy model to describe the magnetic characteristics of amorphous materials such as TbFe2, we determine the low‐temperature dependence of the coercivity as well as the magnetization dynamics of these materials. The results are seen to compare well to experiments whenever data are available. Our model features clusters, each characterized by its anisotropy direction. The exchange‐energy term entering the Hamiltonian is represented by an effective exchange interaction acting in the intercluster regions.

ISSN:0021-8979    

DOI:10.1063/1.345269

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This work deals with soft magnetic polycrystalline samples (YIG) specially prepared for fundamental investigations. These investigations have previously shown, at different times, that macroscopic magnetic properties of such materials could be interpreted by a simple spherical grain model. From theoretical study of this model, a first magnetization curve formulation is proposed. Excellent agreement with measurements in a broad range from weak fields to saturation is shown. In high‐quality materials with a negative magnetostriction constant, because of the very peculiar action on domain walls, parallel compression is shown to be a useful way to compare observation with theory. Quantitative study proves this specific role.

ISSN:0021-8979    

DOI:10.1063/1.345270

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Sputtered CoNiPt films prepared for high‐density magnetic recording media have been studied by Brillouin scattering. The spin‐wave spectra in the film are remarkably broadened with width 13 GHz (full width at half maximum), which is much larger than the width of 3 GHz in a film prepared by vapor deposition. Observation by a transmission electron microscope has clarified that the sputtered film consists of Co crystallites with a diameter of 50–100 A˚, which are separated from each other. The remarkable damping of the spin waves in the sputtered CoNiPt film is caused by the film structure. The film is, however, elastically homogeneous, which is known from the undamped surface acoustic wave spectra. The result shows the segregation of the nonmagnetic Pt‐related alloys takes place between the Co crystallites. The exchange stiffness constant was determined as 2.4×10−9Oe cm2in the sputtered film, which is 1/1.7 that in the vapor‐deposited films.

ISSN:0021-8979    

DOI:10.1063/1.345272

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The magnetoresistive response of long strips of thin ferromagnetic films under external field in the plane of the film is examined using analytic as well as numerical methods. This is done for a range of easy axis directions and external field angles. It is found that the dimensional as well as magnetic parameters are subsumed into two parameters—a zero‐field equilibrium angle &eegr; and a field scaleHS. The magnetoresistive response of the film to an external fieldHAappears in terms of the scaled variable (HA/HS). As a result, the response of a large number of films for a given external field angle, and fixed &eegr;, falls on the same curve when expressed in terms of the scaled variable (HA/HS). This also leads to a reciprocal relation between the sensitivity and range of linearity of the transfer function of a magnetoresistive transducer.

ISSN:0021-8979    

DOI:10.1063/1.345273

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The collective orientation of uniaxial magnetic particles in a Newtonian fluid is reviewed. The quartic term in the equation for the anisotropy torque leads to different conclusions when considering the alignment of a collection of particles than when considering a single particle. Both two‐ and three‐dimensional initial distributions of orientations suggest that larger fields orient the particle assembly more rapidly than the ‘‘optimum’’ field for a single particle.

ISSN:0021-8979    

DOI:10.1063/1.345274

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

57Fe Mossbauer measurements were carried out on Ho0.85Tb0.15Fe2Hx(x=0–3.1) and Dy0.73Tb0.27Fe2Hx(x=0–3.3) in the temperature range 105–360 K. The hyperfine field at the iron site was found to increase slightly with increasing hydrogen concentration in both the systems. The temperature variation studies of the hyperfine fields, the quadrupole coupling constant and the isomer shift suggest the occurance of spin reorientation. The isomer shift studied as a function of concentration indicate the charge transfer from Fe to hydrogen.

ISSN:0021-8979    

DOI:10.1063/1.345275

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The prediction made in J. Appl. Phys.65, 3987 (1989) that the ferroelectric–ferroelastic phase transition atTc=490 K in K3Fe5F15will be accompanied by a change from order to disorder among the Fe2+/Fe3+ions has been confirmed by Mo¨ssbauer spectroscopy. The thermal dependence of both the Fe3+quadrupolar splitting and the Fe3+isomer shift exhibits a smooth decrease with increasing temperature toTc, each with a sharp and reproducible change in slope aboveTc. The average Fe2+quadrupolar splitting (QS) similarly undergoes a major decrease with increasing temperature, with a clear change in slope aboveTc. Furthermore, the thermal dependence of the Fe2+QS distribution shows that the Fe2+/Fe3+order required crystallographically belowTcis not conserved at higher temperatures. The proportion of Fe2+present belowTcis close to the stoichiometric 60% value; the proportion decreases aboveTcrapidly with temperature and becomes less than 50% by 543 K, consistent with increasing delocalization of an Fe2+electron.

ISSN:0021-8979    

DOI:10.1063/1.345219

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The recombination dynamics of GaAs multiple quantum wells as a function of barrier widthsLBare studied in a semiconductor in the range betweenLB=0.87 nm (superlattice) andLB=18.1 nm (uncoupled wells) by means of cathodo‐ and photoluminescence. With decreasingLBthe nonradiative recombination rate is found to be drastically enhanced, where‐as the radiative recombination probability decreases. Thus a pronounced decrease of the quantum efficiency results. The controlled variation of the barrier width is found to be decisive for an unambiguous identification of the origin of the traps which are responsible for the nonradiative processes: Comparison with a theoretical calculation shows that they are localized at the heterointerfaces andnotin the barriers.

ISSN:0021-8979    

DOI:10.1063/1.345220

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The neutral donor‐bound light‐hole free exciton has been observed in AlxGa1−xAs‐GaAs multi‐quantum wells (MQWs). The transition was observed using selective excitation photoluminescence spectroscopy on two nominally 350‐A˚‐wide AlxGa1−xAs‐GaAs MQW structures in the energy region between the light‐hole and heavy‐hole free‐exciton transitions, where no other intrinsic transitions exist. The neutral donor‐bound heavy‐hole free‐exciton transition was also observed in both MQW structures. A third 150‐A˚‐wide MQW structure which showed no evidence of a donor‐bound heavy‐hole free exciton also showed no evidence of a donor‐bound light‐hole free exciton.

ISSN:0021-8979    

DOI:10.1063/1.345221

出版商:AIP    

年代:1990

数据来源: AIP