摘要:

Existing micromagnetic models, based on single domain grains that individually follow coherent rotation during reversal, have been utilized to study the effect of various texture‐induced microstructures on the hysteretic behavior of Co‐alloy thin films with circumferentially textured substrates. The roles of preferential orientation of Cocaxes, grain elongation, and segregation, as well as possible short‐range intergranular coupling, have been examined in an effort to understand the origins of widely observed magnetic anisotropy in these media. Preferentialc‐axis distribution along the track direction yields reasonable remanences and coercivities for both circumferential and radial loops, but the observed loop closure remains unaccounted for byc‐axis distribution alone. Closely packed arrays of elongated grains maintain relative isotropy in terms of magnetostatic interactions, while voids along texture lines contribute to the magnetostatic anisotropy of the film. The limitations of the model are also discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359114

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Remanent magnetization curves of perpendicular magnetic thin films are simulated and measured. The simulations are used to investigate the theoretical influence of the strong demagnetizing field present in these films. Conclusions are drawn from this on how remanence curves should be measured and how they should be corrected for the demagnetizing influence. The experimental part consists of measurements on Fe‐Alumite, Co‐Pt–based multilayers, and Co‐Cr. In addition the latter material is also artificially patterned into microstrips in order to investigate the influence of demagnetization on remanence curves experimentally. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359115

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The temperature dependence of the domain‐wall coercive field of epitaxial magnetic garnets films has been investigated in the entire temperature range of the ferrimagnetic phase, and has been found to be described by a set of parametric exponents. In subsequent temperature regions different slopes were observed, with breaking points whose position was found to be sample dependent. A survey based on literature data as well as on a large number of our own samples shows the general existence of this piecewise exponential dependence and the presence of the breaking points. This type of domain‐wall coercive field temperature dependence was found in all samples in the large family of the epitaxial garnets (about 30 specimens of more than ten chemical compositions) and also in another strongly anisotropic material (TbFeCo). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359116

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Results are outlined of experimental work concerning Slonczewski’s theories explaining 90° coupling: ‘‘loose spin’’ theory and thickness‐fluctuation mechanism. The loose spin theory suggests that 90° coupling originates from paramagnetic impurities in the interlayer of an exchange‐coupled layered structure. The influence of these paramagnetic impurities on the magnetic exchange coupling was studied using the wedge technique. High‐quality single‐crystalline Fe/Ag/Fe samples were prepared in UHV and each sample consisted of two wedges: one wedge with additional Fe deliberately inserted during growth into the Ag interlayer and one wedge with a pure Fe/Ag/Fe structure. The detailed analysis of magneto‐optic hysteresis loops revealed quantitatively the bilinearly and the 90° coupling strength. As predicted by loose spin theory additional Fe in the Ag spacer lead to a strong temperature dependence of the 90° coupling. According to the theory an increase of 90° coupling strength proportional to impurity concentration was detected while the strength of bilinear coupling decreased. For the pure Fe/Ag/Fe structure, a linear increase of the 90° coupling strength with decreasing temperature was observed. This result can be explained within the fluctuation mechanism which creates 90° coupling through a combination of interface roughness and intralayer ferromagnetic exchange. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359117

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Conventional angle‐dependent ferromagnetic resonance (FMR) measurements on an epitaxial (001) Fe film grown on a GaAs substrate were performed as a function of the orientation of the external magnetic fieldBextfor three configurations: One withBextin the film plane and two withBextout of plane starting in plane in different crystallographic orientations. From these measurements the magnetizationM, the crystalline anisotropy constantsK1andK2, the surface anisotropyKsand an additional uniaxial anisotropyKuwere deduced self‐consistently. The temperature dependence ofK1andMwas investigated for the in‐plane [110] orientation in the range from 100 to 570 K. In addition, locally resolved photothermally modulated FMR measurements were carried out to study the homogeneity of the magnetization and of the crystalline anisotropy across the film. Disturbances of both magnetic parameters as a function of position were observed which are related to local inhomogeneities in the semiconducting substrate. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359519

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

It is proposed that the ferroelectric fatigue is caused by alternating mechanical stresses induced piezoelectrically. It is shown that the mechanical stresses that develop upon switching are sufficient to cause significant mechanical fatigue after the similar number of cycles after which the ferroelectric fatigue is typically observed. It is proposed that the degradation of the ferroelectric properties is a direct consequence of the mechanical fatigue. It is attempted to explain some of the reported correlations between ferroelectric fatigue and microstructure, temperature, test conditions, and electrode material. It is proposed that electromigration and chemomechanical effect are essential in the mechanism of the effect of electrode material on ferroelectric fatigue. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359118

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A layered sphere Bruggeman effective‐medium model was developed to describe the dielectric constant of a porous ceramic composite having potential for use as a very low dielectric constant inorganic material for microelectronic packaging. The uniqueness of this model is that it incorporates a hollow sphere geometry and thus fits closely the microstructure of the dielectric composite in a broad range of compositions. Samples of the composite were prepared by adding hollow alumina‐silica alloy ceramic spheres to a cordierite matrix. Their dielectric properties were characterized as a function of volume fraction of hollow spheres. The measured results were in good agreement with the model prediction. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359119

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Induced ferroelectricity was observed in epitaxially grown BaxSr1−xTiO3(BST) thin films with thicknesses of about 220 nm. The BST films with various Ba content were deposited at 600 °C on Pt/MgO substrates, by radio frequency magnetron sputtering with double targets, BaTiO3and SrTiO3. The epitaxial growth of the BST films was confirmed with x‐ray‐diffraction and reflection high‐energy electron‐diffraction analyses. TheD–Ehysteresis curve and the Curie temperature shift confirmed the BST films with Ba contentx≥0.44 had ferroelectricity at room temperature. The mechanism of the ferroelectricity appearance was discussed in relation to the elongation of thecaxis in the thickness direction, caused by lattice mismatch between Pt and BST. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359120

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The epitaxial‐like BaTiO3(BTO) films with good ferroelectricity are obtained both on (001)SrTiO3(STO) single crystal and on CeO2buffered silicon substrate by pulsed laser deposition. The deposition parameters need to be stringently controlled in order to grow BTO films with good crystallinity. The BTO films grown on YBa2Cu3O7−x(YBCO)/CeO2/STO substrates are epitaxial, as confirmed by rocking curve, &fgr; scan, and wide‐angle x‐ray‐diffraction techniques. The alignment ofaandbaxes of BTO films on YBCO/CeO2/Si substrate is, however, not as perfect as BTO film on YBCO/STO substrate. The BTO/YBCO/CeO2/Si films are only (00l) textured. The ferroelectric property measurement, using the YBCO layer as the base electrode material, shows that the remanent polarizationPrand coercive fieldEcof the BTO/YBCO/CeO2/Si films (Pr=3.6 &mgr;C/cm2,Ec=11.1 kV/cm) are, however, as good as those of the BTO/YBCO/STO films (Pr=4.0 &mgr;C/cm2,Ec=12.5 kV/cm). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359121

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experimental results are presented for the physical origins of room‐temperature photoreflectance features of a AlGaAs/GaAs single‐quantum well structure. The spectra exhibit well‐defined Franz–Keldysh oscillations which overlap with photoreflectance features due to the quantum well and complicate the determination of the energies of the transitions within the quantum well. The origin of the Franz–Keldysh oscillations are determined using wet chemical etching to selectively remove grown layers down to the substrate. The resulting spectra are presented as a function of etch depth which allows the magnitude of the built‐in electric fields to be determined and reveals the location within the quantum well structure where the Franz–Keldysh oscillations originate. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359122

出版商:AIP    

年代:1995

数据来源: AIP