摘要:

The crystal structure and magnetic properties of LaCo13−x−yFexSiycompounds were investigated by means of x‐ray powder diffraction and magnetization measurements. The substitution of Si for Co induces an order–disorder transition from the cubic NaZn13‐type to its tetragonal derivative structure, while the substitution of Fe for Co does not induce such a phase transition. After annealing treatment, the homogeneous range of the cubic phase is narrowed and that of the tetragonal phase is extended. From crystallographic and thermodynamic points of view, the sta‐ bility of the cubic and the tetragonal phases is discussed. The measured magnetic moment of LaCo13−x−yFexSiycoincides well with the theoretical prediction based on the magnetic valence model. Within the framework of this model, LaCo13−x−yFexSiycompounds can be considered as strong ferromagnets and their magnetic moment can be theoretically predicted. The composition dependence of Curie temperature is discussed within the mean field approximation. At higher iron concentration the decrease of Curie temperature with Fe concentration might be attributed to the increase of the number of antiferromagnetically coupled Fe–Fe pairs and the decrease of the ferromagnetic coupling between transition metal atoms. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362786

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The magnetic characteristics of 0.2×0.4×0.02 &mgr;m3cobalt islands were investigated using magnetic force microscopy in the presence of an applied field. The islands were noninteracting and showed a wide variety of single and multidomain configurations. The distribution of magnetization directions supports earlier models which suggest that crystalline anisotropy plays a dominant role in establishing a dispersion of easy axis directions about the long axis of the particles. The magnetic evolution, involving rotation and switching of individual islands, was observed at various points along the microscopic magnetization curve. A magnetization curve of an ensemble of islands was derived from the images and compares remarkably well with macroscopicM–Hmeasurements. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362787

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have studied the evolution of the magnetic in‐plane anisotropy in epitaxial Fe/GaAs films of both (001) and (1¯10) orientation as a function of the Fe layer thickness using the longitudinal magneto‐optic Kerr effect and Brillouin light scattering. Magnetization curves which are recordedinsituduring film growth reveal a continuous change of the net anisotropy axes with increasing film thickness. This behavior can be understood to arise from the combination of a uniaxial and a cubic in‐plane magnetic anisotropy which are both thickness dependent. Structural analysis of the substrate and Fe film surfaces provides insight into the contribution of atomic steps at the interfaces to the magnetic anisotropy. Changing the degree of crystalline order at the Fe–GaAs interface allows us to conclude that the magnetic anisotropies are determined by atomic scale order. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362788

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Fully dense Sm2Fe17Nxbulk bodies with porosities less than 5% were prepared by shock compression in a certain low‐pressure region, using the magnetically aligned powder pellets with an initial porosity of 46%–52% and without binder. Below a driving shock pressure (single shock wave using a copper standard capsule) of about 10 GPa, the recovered specimens did not consolidate well, and above about 20 GPa they began to decompose to &agr;‐Fe and Sm nitride. The consolidated state and porosity depended on the driving shock pressure, the thickness and porosity of the starting powder pellet, and the thickness of the impact plate. It was found that the shock consolidated bulk bodies had a Curie temperature of approximately 475 °C, and that the magnetic properties were sensitive to shock pressure, porosity, alignment, etc. The largest values of coercivity and maximum energy product of the recovered bulk specimens prepared in this study were 7.1 kOe and 16.8 MGOe, respectively. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362789

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ferroelectric polarization reversal in polyurethane [poly(trimethylene heptamethylene dicarbamate)] and low molecular weight urethane (pentamethylene stearyl dicarbamate) has been studied by a spectroscopic technique; Fourier transform infrared measurement of the samples while applying an external electric field. These samples showed typical electrical displacement versus electric‐field hysteresis loops and pyroelectric properties. It is considered that the above properties result from urethane dipole rotation in the crystal under an external electric field. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362790

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electrical conductivity of two different types of lead iron niobate thin films prepared by a modified sol gel method have been studied. PEN films rapid thermally processed at 425 °C/30 s and at 650 °C/1 s exhibited a highly nonlinear leakage current behavior. At room temperature space charge limited current conduction was not observed for any of the samples. Due to enhanced thermal detrapping at higher measurement temperatures the conduction became bulk limited and the leakage current was controlled by Poole–Frenkel emission. In samples processed at 650 °C/1 s the injection of electrons occurred through a Schottky barrier near the bottom electrode resulting from a higher processing temperature. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362784

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Lead iron niobate thin films were synthesized using a modified sol gel method. Films processed at temperatures as low as 400 °C had a dielectric constantK≊400.Kof ≊1000 and a low loss factor tan &dgr;≊0.02 were obtained for films rapid thermally processed between 650–700 °C. Films processed at ≊400 °C showed a more linear behavior and were able to endure higher electric fields up to 1.6 MV/cm. The remanent polarizationPrand coercive fieldHcfor films processed at 650 °C/1 s were 4.5 &mgr;C/cm2and 40 kV/cm, respectively. Leakage current densities of films increased with processing temperature and were of the order of 4 and 10 nA/cm2for films multiply processed at 425 °C/30 s and 650 °C/1 s, respectively. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362791

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The behavior of domain walls in KNbO3single crystals with temperature variation from room temperature to 300 °C has been investigatedinsituby a heating visualization system. It has been observed that domain walls show active behavior in a small temperature range from the phase transition temperature of 225 °C, the range being about 10 °C in the orthorhombic phase and 15 °C in the tetragonal phase. The 90° domain walls are generated randomly and extend themselves rapidly within the crystal in high density. The 60° domain walls, which are only observed in orthorhombic phase, do not appear randomly but are formed along the boundary of intersecting 90° domain walls. The results suggest that the 90° domain walls are most likely caused by microdefects within the crystal, and that dislocations at the junction of intersecting 90° domain walls supply nucleation sites for the 60° domain walls. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362792

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this work the dielectric reliability of thermally grown ultrathin 3 nm SiO2layers in poly‐Si/SiO2/Si structures is examined. This is compared with a study of the defect generation in the 3 nm gate oxide during tunnel injection of electrons. In these ultrathin SiO2layers, direct tunneling of electrons becomes very important. An increase of the direct tunnel and Fowler–Nordheim tunnel current during high‐field stressing was observed and is explained by the creation of a positive charge in the oxide associated with slow interface traps. It is demonstrated that a higher current instability corresponds with a lower charge to breakdown value (QBD) of the oxide. From these results we conclude that the creation of slow interface traps is an important precursor effect for the 3 nm gate oxide breakdown. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362794

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have been successful in obtaining temperature‐stable crystallized thin film of (Zr,Sn)TiO4. Preferential (111)‐oriented (Zr,Sn)TiO4thin film was prepared by pulsed laser deposition. Effects of crystallization were elucidated based on a comparison of electric properties of crystallized and amorphous (Zr,Sn)TiO4film. For crystallized film, the temperature coefficient of capacitance (TCC) was 20 ppm/°C at 3 MHz and the dielectric constant &Vegr;r=38 in the microwave range of 1–10 GHz. These values are superior to those for amorphous film (TCC=220 ppm/°C, &Vegr;r=27). The crystallization of this material was found quite effective for improving dielectrical properties. Atomic force microscope images showed the surface morphologies of crystallized and amorphous film of (Zr,Sn)TiO4to differ. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362795

出版商:AIP    

年代:1996

数据来源: AIP