摘要:

A series of bcc‐Co(001)/Ge/Co trilayers was grown on a GaAs(001) substrate by the molecular beam epitaxy technique. The optical and magneto‐optical properties of the samples were studied. An oscillatory variation of the magneto‐optical Kerr effect (MOKE) with the thickness of the Ge spacers was observed. We conclude that the effective optical constants as well as the real and imaginary off‐diagonal element of the dielectric tensor should be considered in explanation of the MOKE activities since both have a large influence on the MOKE oscillations. Moreover, the coercivity and magnetization also oscillate with the Ge layer thickness. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117571

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The magnetic and transport properties of La2/3−xNdxCa1/3MnO3(x=0–0.67) are studied. Two magnetic transitions occur in compounds with compositionx=0.1–0.4, leading to a low moment state at high temperature and a high moment state at low temperature. A metal–insulator transition was observed forx≤0.4 between the two magnetic transitions. An electronic and magnetic phase diagram is depicted on a temperature–tolerance factor plane. The interesting feature of this diagram is the appearance of a new metamagnetic phase. Present investigation suggests that the tolerance factor is not the only parameter determining the lattice effects. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117572

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Giant magnetoresistance La–Ca–Mn–O films, with 32% at 5.7 K and 20% near room temperature change in resistivity ( &Dgr;&rgr;/&rgr;0) at a magnetic field of 4.7 T, have been deposited on Si (100) substrates using pulsed laser deposition. The effects of preparation conditions on the properties of the films are described. Deposition at a high temperature shifts the resistivity peak to lower temperatures and simultaneously increases the maximum resistivity value. Annealing at a high temperature, however, produces the opposite effect on the resistivity behavior. Our results suggest that the oxygen stoichiometry in the films is a crucial factor in causing the ferromagnetic transition and the noted peak of the resistivity characteristics to shift to higher temperatures. Some possible mechanisms are suggested. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117573

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Direct ferromagnetic antiferromagnetic exchange biasing energy is determined by small reversible rotations of the magnetization away from the unidirectional easy axis using an externally applied magnetic field. The angle the magnetization makes relative to the easy direction is determined by measuring the anisotropic magnetoresistance. This technique gives energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO. An apparent Co thickness variation of the experimentally determined exchange biasing interface energy indicates the Co magnetization is not uniform but probably spirals through the thickness of the film. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117574

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on magnetotransport measurements of spin valve films that have been fabricated into rectangular stripes with Au current leads. The spin valve films consisted of two magnetic NiFe layers separated by a nonmagnetic Cu layer. The top NiFe layer was magnetically pinned by a FeMn layer with an effective pinning field of 12 kA/m (150 Oe). After device fabrication, the transport properties changed dramatically as the stripe‐height of the device was decreased below 1 &mgr;m. Internal demagnetizing fields and magnetostatic interactions between the magnetic layers dominated the magnetic response. These interactions change the biasing point and the linearity, and cause a decrease in sensitivity to field changes. We have developed a simple single‐domain rotation model that includes magnetostatic, anisotropy, and exchange interactions to describe the magnetic behavior, from which we calculate the transport response. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117575

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new class of photodetectors is proposed, based on localized heating of an ultrathin metallic film due to absorption of individual photons. For a 1 eV photon, the transient temperature rise can be of order 10 K or greater in a nonequilibrium ‘‘hotspot’’ on the nm spatial scale and ps timescale. If current is flowing in a metallic film with a temperature‐dependent resistance, such a hotspot can give rise to a voltage pulse. This can provide the basis for an ultrafast photodetector with spectral sensitivity, in contrast to a conventional bolometer. Prospects for practical realization of infrared photodetectors based on this mechanism are discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117576

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Dark, nonemissive defects form on the metal cathode in most molecular organic and polymer‐based light emitting devices and eventually lead to the failure of the device. These defects have been characterizedinsituusing optical microscopy andexsituusing atomic force microscopy and Auger electron spectroscopy. On the basis of these observations, an electromigration mechanism for the formation of dark spot defects is proposed. The high current density required to operate polymer‐based light emitting devices leads to electron‐induced diffusion of the Al cathode when a short circuit forms in the emissive polymer layer. This process results in a ‘‘pileup’’ of metal at the short circuit (anode) and a surrounding circular region where the Al is depleted, appearing as a dark spot on the cathode. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117577

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a sensor for the atomic force microscope (AFM) where a silicon cantilever is micromachined into the shape of interdigitated fingers that form a diffraction grating. When detecting a force, alternating fingers are displaced while remaining fingers are held fixed. This creates a phase sensitive diffraction grating, allowing the cantilever displacement to be determined by measuring the intensity of diffracted modes. This cantilever can be used with a standard AFM without modification while achieving the sensitivity of the interferometer and maintaining the simplicity of the optical lever. Since optical interference occurs between alternating fingers that are fabricated on the cantilever, laser intensity rather than position can be measured by crudely positioning a photodiode. We estimate that the rms noise of this sensor in a 10 hz–1 kHz bandwidth is ∼0.02 A˚ and present images of graphite with atomic resolution. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117578

出版商:AIP    

年代:1996

数据来源: AIP