摘要:

The dynamics of the detailed micromagnetic structure of domain walls in thin films are computed by numerical integration of the Landau‐Lifshitz‐Gilbert equation. The temporal and spatial variations of wall structure under a suddenly applied in‐plane field lying in the plane of the wall are investigated. The structure is substantially changed at in‐plane field strengths of only 2% of the anisotropy field,Hk. A critical in‐plane field value is reached at about 2.25% ofHk; at this point, the time required for the wall structure to reach equilibrium is a maximum. This settling time is also a function of the damping parameter &agr;. For &agr;≳0.1, the settling time is found to be nearly proportional to &agr;; for &agr;≲0.1, the settling time becomes larger as &agr; decreases due to oscillations of the wall structure. In the language of harmonic oscillators, the micromagnetic structure appears underdamped for &agr;<0.1, critically damped at &agr;?0.1, and overdamped for &agr;≳0.1.

ISSN:0021-8979    

DOI:10.1063/1.325628

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Measurements of the magnetic susceptibility of theR2In compounds from 4.2 to 270 K have been made. All compounds except Y2In and Sm2In exhibit Curie‐Weiss behavior at high temperatures with effective magnetic moments agreeing reasonably well with the free‐ion 3+ picture modified by RKKY exchange except for Gd2In, which gives an unusually high value for the effective moment. With the exception of Y2In all other members exhibit susceptibility maxima. Gd2In, Tb2In, and Dy2In order antiferromagnetically. Gd2In is a metamagnetic compound. For the three compounds Ho2In, Er2In, and Tm2In there is no indication of their type of ordering at low temperatures. The isotherm at 4.2 K of Nd2In shows a ferromagnetic or ferrimagnetic behavior.

ISSN:0021-8979    

DOI:10.1063/1.325629

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Experimental results for magnetostrictive generation of low‐frequency standing elastic waves in polycrystalline and amorphous ferromagnetic materials are given. By exciting magnetized samples with bursts of magnetic impulses, extensional and torsional modes of damped wave propagation were observed. These propagation patterns are qualitatively explained by means of the theory of linear magnetoacoustic coupling taking into account the residual stresses alone. A comparison of the magnetomechanical behavior of the materials investigated has been made by studying the conditions of reversible magnetostriction and the magnetic damping. In particular, in the Ni rod, it was possible to clarify the log decrement behavior on the basis of the reversible magnetomechanical permeability and the &Dgr;Eeffect measured.

ISSN:0021-8979    

DOI:10.1063/1.325630

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The magnetic and atmospheric corrosion characteristics of Fe1−xPdxfilms are discussed. The polycrystalline films are prepared by codeposition in a UHV system using separate electron‐beam‐heated Fe and Pd sources. Some trends in their properties appear to be connected with the crystal structure which is bcc forx≲0.31 and fcc for higher Pd concentrations. All but films with high Pd content are magnetically soft or nearly so and have an in‐plane uniaxial anisotropy. The anisotropy field decreases with increasing deposition temperature and is also smaller for the fcc structure. The coercivity depends principally on film composition and deposition temperature. Perpendicular anisotropy is found in films with high Pd concentrations. The lower Pd content bcc structure is relatively prone to corrosion in a high‐humidity atmosphere containing controlled trace quantities of acid‐forming pollutants (Cl2, SO2, etc.), but the fcc structures are quite inert. Possible mechanisms governing the relationship of the magnetic, corrosion, and structural properties to the deposition parameters are explored.

ISSN:0021-8979    

DOI:10.1063/1.325631

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Acicular &ggr;‐Fe2O3particles were heated at 90°C in alkali solution containing Co2+and Fe2+. The coercivity of the resultant particles remarkably increased with the increasing Co2+/Fe2+ratio, and in the neighborhood of the Co2+/Fe2+ratio of 0.4, reached a maximum value. When the particles with a Co2+/Fe2+ratio of 0.5 were dissolved in hydrochloric acid, the cobalt content and the coercivity were rapidly decreased with increasing dissolved weight. Iron‐cobalt ferrite was expected to grow on the surface of &ggr;‐Fe2O3particles. The increase of coercivity was attributed to the iron‐cobalt ferrite.

ISSN:0021-8979    

DOI:10.1063/1.325632

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A new and very sensitive method (1 part in 1019) for studying nonlinear properties of metallic systems under the influence of radio-frequency fields is described. The method is applied to a study of the intermodulation generation at 150 MHz in nickel as a function of a dc field and as a function of the power of the two simultaneously applied rf fields at 146 and 148 MHz. As the dc field is increased for a given applied rf power, the intermodulation signal shows a number of linear regions of decrease on a semilogarithmic graph. Different results are obtained which depend on the relative orientations of the dc and rf magnetic fields. The power of the intermodulation signal shows a cubic or quadratic dependence on the power of the applied rf fields for low or high values of the dc field, respectively. These results are discussed in terms of the interaction of the rf field with the domain walls using a recent model of an electroplated nickel domain structure proposed by others.

ISSN:0021-8979    

DOI:10.1063/1.325633

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Pressure induced changes in the reflectivity of SmSe have been investigated up to 70 kbar hydrostatic pressure, using the gasketted diamond anvil high‐pressure x‐ray apparatus in conjunction with an optical microspectroscopic system. The effect of Nd substitution on the lattice parameter, resistivity, and color of SmSe has also been studied. Reflectivity data for GdSe at ambient pressure have been obtained for comparison with the metallic phase of SmSe. With increasing pressure the color of the sample (as observed in reflected light) goes through a sequence of changes, from black, steel‐blue, deep purple, reddish purple, copperlike metallic color to bronze yellow at the highest pressure. From the reflectivity data, the static conductivity has been evaluated and is compared with the dc conductivity, previously measured on SmSe single crystals under hydrostatic pressure. Deviations from Drude theory indicate that the interband contribution to the dielectric constant plays an important role in determining the sequence of metallic colors observed in metallic rare‐earth monochalcogenides.

ISSN:0021-8979    

DOI:10.1063/1.325634

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Chromium has been observed to be responsible for a band of absorption in semi‐insulating GaAs. The corresponding absorption coefficient has been carefully calibrated using three different chemical analysis methods. It is shown that the spatial distributions of Cr in semi‐insulating GaAs ingots can be obtained very easily using optical absorption measurements and that the segregation coefficient of Cr in GaAs is equal to 8.9×10−4. The nature of the optical transitions due to the presence of Cr is discussed in detail and it is shown that they occur mainly on the Cr3+in semi‐insulating material.

ISSN:0021-8979    

DOI:10.1063/1.325635

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The extrinsic photoconductivity of GaP doped with the donors S, Se, Te, or Si and with the acceptors C or Zn has been measured at liquid‐helium temperatures in the 400–3000‐cm−1region of the infrared. The ionization energy of these impurities was determined to be 103.5, 102, 90, and 78 meV, respectively, for the donors and 49 and 71 meV, respectively, for the acceptors. Dips in the spectral response of the donors are interpreted as primarily due to electron capture from the conduction band to excited states of the donor atoms together with emission of LA(X) and LO(&Ggr;) phonons. Excited states are observed in the photoconductive spectrum to which transitions from the ground state are forbidden in optical absorption. The spectral response of the acceptors show a prominent oscillatory response due to interaction with LO(&Ggr;) phonons and to capture into the acceptor ground state. Smaller dips due to hole capture from the valence band to excited states are also observed in thep‐type crystals, but the excited states responsible have not all been identified in the acceptor spectra.

ISSN:0021-8979    

DOI:10.1063/1.325636

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The effect of the primary light intensity (corresponding to the fundamental absorption edge) on the infrared quenching of photocapacitance (PHCAP IR quenching) in CdS : Cu evaporated films has been studied. Two methods, viz., the two‐beam and three‐beam methods, for PHCAP IR quenching on detecting deep Cu levels are developed. It has been found that PHCAP IR quenching depends on the primary light intensity, that is, the rates for capturing holes into Cu deep acceptor levels [Cu+levels and (Cu+Cu+) levels] vary as the primary light intensity changes. The experimental results are consistent with the calculations based on the three‐state model of Cu quantitatively. The photoionization cross sections and thermal emission rates of holes were also measured.

ISSN:0021-8979    

DOI:10.1063/1.325638

出版商:AIP    

年代:1979

数据来源: AIP