摘要:

Using theoretical expressions for the magnetization curve of polycrystalline ferrimagnets given previously, we have considered the effect of a grain size distribution on the magnetization versus applied magnetic field curve. We have observed the effects of various theoretical probability distribution functions and compared them with an experimental curve of yttrium iron garnet, Y3Fe5O12. The best fitting was obtained with a normal logarithmic distribution function for the grain size distribution of the sample.

ISSN:0021-8979    

DOI:10.1063/1.334353

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Different target configurations have been used to directly synthesize Sm‐Co based films by selectively thermalized rf sputtering onto heated substrates in an in‐plane magnetic field. Samples have been sputtered so that in certain cases a systematic gradient in Sm‐to‐Co concentration was created along the length of the substrates and in other cases so that films of a fixed uniform composition were deposited. Small subregions of a single substrate then serve as samples of a specific composition. For the Sm‐to‐Co composition range from 70 to 95 at. % Co gradient synthesized samples exhibit high magnetization and moderate intrinsic coercive forces. The maximum energy product of 20 MG Oe was obtained for a sample with 90.6 at. % Co containing mostly the Sm2Co17phase. In addition, samples were synthesized from uniform composition targets at certain fixed compositions. Films sputtered from uniform composition Sm2(Co, Fe, Zr)17targets exhibited square in‐plane hysteresis loops and static energy products up to 21.2 MG Oe. It was observed that uniform composition SmCo5films could be grown which exhibited either the (200) or the (110) texture as a function of the sputtering rate. Relatively higher sputtering rates of approximately 5 A˚/sec resulted in the (200) texture growth pattern while lower rates resulted in (110) textured films. These differently textured SmCo5films differ in both their microstructure and magnetic properties. The (110) textured film are finer in microstructure and magnetically harder than the (200) films. The uniform composition SmCo5films of either texture in general were of smaller grain size and higher coercive forces than the SmCo5subregions from films sputtered with a composition gradient spanning the 1–5 phase. A uniform composition SmCo5film sputtered at 1.5 A˚/sec which was (110) textured exhibited an intrinsic coercive force of 23 kOe and an energy product of 18 MG Oe at −63 °C. The high‐energy products reported here are due to both the high induction and to the squareness of the in‐plane hysteresis loops when measured in the direction parallel to the field applied during the sputter synthesis.

ISSN:0021-8979    

DOI:10.1063/1.334354

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Amorphization produced by ion implantation and subsequent crystallization produced by thermal processing have been investigated in films of (SmYGdTm)3Ga0.4Fe4.6O12garnet by transmission electron microscopy, incorporating a special cross‐sectioning technique. These films were produced by liquid‐phase epitaxy on {111} garnet substrates and subsequently implanted with ions of deuterium at 60 keV and doses ranging from 0.50 to 4.5×1016D+2/cm2and ions of oxygen at 110 keV and doses ranging from 0.95 to 8.6×1014O+/cm2. The amorphization process evolves in four separate stages: (1) an implanted (crystalline) band, delineated by the implantion strain profile, forms at doses of about 0.50×1016D+2/cm2/ and 0.95 O+/cm2, (2) isolated amorphous regions of about 10 nm in diameter form at doses of about 1.0×1016D+2/cm2and 1.9×1014O+/cm2, (3) the amorphous regions merge to form a continuous band below the implanted surface at doses of about 3.0×1016D+2/cm2and 5.7×1014O+/cm2, and (4) this band expands to the implanted surface at larger doses. Amorphization is caused by implantation with oxygen, but prior implantation with deuterium sensitizes the lattice by increasing the strain. The crystallization process evolves in three separate stages: (1) small crystallites, about 10 nm in size, form throughout the entire amorphous band after annealing for 10 min at 350 °C, (2) larger crystallites nucleate and grow from the implanted surface and amorphous/crystalline interface after annealing for 10 min at 450 °C, and (3) these crystallites grow in size until they merge to form a continuous polycrystalline layer. Some epitaxial regrowth of the monocrystalline into the amorphous region is also observed. Details of these processes are interpreted in terms of atomic displacement mechanisms and compared with corresponding changes of certain magnetic properties.

ISSN:0021-8979    

DOI:10.1063/1.334355

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Ferromagnetic resonance spectra and x‐ray rocking curves were used to measure magnetic and strain profiles of Gd, Tm, Ga substituted yttrium iron garnet films implanted with H2+at 120 keV and at doses in the range (3–80)×1015ions/cm2. The maximum strain occurred at a depth of 3600 A˚, reaching a value of 2.9% at 40×1015ions/cm2. At the highest dose, the garnet was amorphous in that region which had highest strain at lower dose. The strain has two components, one due to damage and one due to the presence of the hydrogen atoms. The second component disappears for annealing temperatures above 400 °C, at which temperature the hydrogen has been reported to be largely desorbed. The reduction of the first component with annealing follows the same pattern as other implant elements. The magnetic anisotropy exhibits a large anomalous nonlinear increase with dose. The excess over other implantation elements disappears for annealing temperatures above 400 °C. There is no significant change in gyromagnetic ratio with dose or annealing temperatures up to 600 °C.

ISSN:0021-8979    

DOI:10.1063/1.334356

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The basic concepts of a self‐consistent domain theory for the class of ideal soft ferromagnetic media is unfolded. The treatment is based on micromagnetic equilibrium and stability equations which are simplified by removing the contributions due to the intrinsic anisotropy and the spatial variation term in the exchange energy density. Only the solenoidal magnetization distributions in thin film objects are investigated. This limitation makes confinement to two‐dimensional dipole distributions possible. Cauchy’s method of characteristics is employed to derive dipole distributions that satisfy the relation ∇⋅M=0, whereMis the magnetization, and the constitutive equation. It is proved that the characteristic base curves are straight lines perpendicular to the magnetization vector. In an ellipse, four different characteristic base curves that do not coincide intersect at one single point in certain regions, thus generating ambiguities in the magnetization direction. It is demonstrated that these ambiguities originate in the incompatibility of the magnetization distribution that is imposed by the various segments of the edge of the ellipse. Based on differential geometrical principles, a partitioning of the edge into segments is introduced, and along with it two adjoining regions in which the magnetization direction is uniquely determined are defined. It is proved that a domain wall is required in the cross section of both regions to accomplish a dipole configuration in stable equilibrium. Experimental confirmation is given by means of the ferrofluid pattern of a 3500‐A˚‐thick Permalloy layer with elliptical geometry.

ISSN:0021-8979    

DOI:10.1063/1.334357

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A method for measuring spatially resolved high‐resolution nuclear magnetic resonance spectra for a spatially heterogeneous complex object has been examined by making images of several phantoms. The factors which determine the image quality are discussed from both theoretical and experimental viewpoints. Especially, the effects of field inhomogeneity, originating from magnet inhomogeneity and nonuniform magnetic susceptibility of the object itself, are examined in detail. The indirect spin‐spin coupling effect on imaging results is theoretically discussed. Although mathematical treatments are given for three‐dimensional objects, actual measurements were performed for spatially limited two‐dimensional regions by slicing the three‐dimensional objects using a selective excitation technique. The results show that the present method is feasible for practical chemical shift imaging purposes.

ISSN:0021-8979    

DOI:10.1063/1.334358

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

After implantation of ytterbium (Yb) in InP, GaP, and GaAs and subsequent annealing, we observed sharply structured photoluminescence bands at around 1.00 &mgr;m (1.24 eV). These emissions are assigned to the internal 4f‐4ftransitions2F5/2→2F7/2of Yb3+(4f13). Isochronal annealing studies and variations of the implantation dosages for Yb in InP were performed to optimize the luminescence efficiency and to decide whether there are different Yb centers responsible for the luminescence bands. It is shown that the dominant luminescence band arises from a cubic Yb3+center which resides substitutionally on a cation site (In or Ga). Zeeman measurements and photoluminescence excitation spectroscopy further support this interpretation. The influence of electron irradiation on the luminescence efficiency of InP:Yb has been investigated. It is found that the Yb3+luminescence intensity is only weakly affected, while the near band‐edge emission is strongly quenched.

ISSN:0021-8979    

DOI:10.1063/1.334359

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Photoluminescence and Hall‐effect measurements on neutron transmutation doped liquid‐phase‐epitaxial GaAs layers were performed. The obtained results clearly point out that at least a part of the Ge atoms introduced by transmutation of Ga leave their original lattice site behaving as acceptors. The probable cause of these displacements are the recoils during &ggr; and &bgr; emissions from the unstable Ga isotopes.

ISSN:0021-8979    

DOI:10.1063/1.334360

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Two‐photon absorption spectra of GaAs were obtained using photoconductivity techniques. At zero magnetic field, the spectrum has a photon energy (ℏ&ohgr;) dependence of (2ℏ&ohgr;–Eg)3/2just above the energy band gap (Eg), and can be described without considering exciton enhancement effects. Oscillatory behavior in the photoconductive response at zero field as a function of incident two‐photon energy has been observed and shown to be due to the interaction of the photoexcited electrons and longitudinal optical phonons. At high magnetic fields, the spectra are quantitatively interpreted in terms of a modified Pidgeon–Brown energy band model.

ISSN:0021-8979    

DOI:10.1063/1.334361

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

When an extrinsic, direct band‐gap semiconductor sample is irradiated by photons of an energy higher than the energy of the band gap between valence and conduction bands, excess electron‐hole pairs are generated which, while diffusing through the sample, produce luminescence via radiative recombination. If, furthermore, the intensity of the impinging beam of photons is modulated sinusoidally, the luminescence radiation escaping from the sample will be phase shifted with respect to the original photon beam in a characteristic way. It will be shown that by measuring the phase shift at different modulation frequencies, the Shockley‐Read‐Hall lifetime of minority carriers may be ascertained. The method is nondestructive inasmuch as there is no need to fabricatep‐njunctions or Ohmic contacts, nor is it necessary to remove already existing Ohmic contacts or angle lap the surface, etc., procedures often needed when determining lifetimes with the scanning electron microscope (in which case ap‐njunction must be present).

ISSN:0021-8979    

DOI:10.1063/1.334362

出版商:AIP    

年代:1985

数据来源: AIP