摘要:

The propagation of ultrasonic waves in iron‐in‐mercury magnetic fluids has been studied by a continuous wave (CW) method. The CW method proved to be adequate for studying the velocity change (&Dgr;V) due to an external magnetic field. The magnitude of &Dgr;V was about 0.3% for field of 100 G. &Dgr;V was also measured at two field angles, when the direction of ultrasonic propagation is either perpendicular or parallel to the magnetic field directions. The characteristic time was found to be about 60 sec, which is of the same order as found from other magnetic measurements in the same sample. This fact indicated that there are aggregates of the size 104A˚ in the fluid.

ISSN:0021-8979    

DOI:10.1063/1.330951

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We have adapted a classical nonresonance method to measure the magnetic susceptibility of liquid3He at low temperature. With modern instrumentation the method has sufficient sensitivity to measure the nuclear susceptibility and nuclear relaxation time of3He. The technique is based on the fact that for two locations on the free surface of a liquid in equilibrium, the height difference is given by h2−h1= &khgr;(H22−H21)/2g, where H2and H1are the local values of the magnetic field at the liquid surface, &khgr; is the magnetic susceptibility per unit mass, and g the acceleration of gravity. Change in the liquid level between closely spaced parallel electrodes changes their capacitance, which is used to obtain h2−h1. Differences in &khgr; as small as 10−10emu/gm were easily detected in these measurements. The method can be applied to other weakly magnetic liquids and, in modified form, to solids.

ISSN:0021-8979    

DOI:10.1063/1.330952

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Monte Carlo techniques have been used to investigate the effects of magnetostatic and repulsive particle interactions on the formation of agglomerates in a magnetic fluid. The dependence on particle size and applied field of the form of the agglomerates was studied using a spatial distribution function which allows a quantitative distinction to be made between clusters and anisotropic chain structures. Magnetization curves have been calculated for magnetic particle sizes varying from 5 to 15 nm with and without magnetostatic interactions. For the larger particle sizes, it was found that the initial susceptibility is reduced in the presence of interactions. This is associated with the presence of pronounced agglomeration in zero field, where open clusters are formed. As the applied field is increased the clusters break up to form long chains aligned in the field direction. At intermediate particle sizes, there is evidence of magnetic field induced agglomeration leading to the formation of dimers and trimers preferentially aligned in the field direction. The smallest particle size showed little evidence of ordering even in strong applied fields, since thermal disordering dominates the situation.

ISSN:0021-8979    

DOI:10.1063/1.330953

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Discrete Fe‐N phases which are difficult to prepare by common chemical methods have been synthesized by rf sputtering. Some of these phases are relevant in the Fischer‐Tropisch synthesis of synfuels. Single Fe‐N phases as well as the desirable mixtures have been synthesized by a careful control of various sputtering parameters. These films showed varied columnar microstructure with the columns perpendicular to the film plane. Magnetic anisotropy measurements for selected samples containing pure Fe4N, &egr;‐Fe3N, and Fe4N+&agr;Fe have been carried out. The anisotropy components when the field (H) is perpendicular or parallel to the columns show significant differences in the magnetization versus H curves up to fields of 8 kOe at room temperature and evidence for superparamagnetism. These results are explained on the basis of structural anisotropy of the columnar structure of the films. Mo¨ssbauer results for the &egr;‐nitride film are compared with those reported in the literature and again related to the microstructure.

ISSN:0021-8979    

DOI:10.1063/1.330954

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In order to prepare berthollide type of iron oxide (i.e., nonstoichiometric magnetite; FeOx:1.34<×<1.5) thin films, iron targets were sputtered in pure water vapor at the pressure of 2×10−3Torr by using a high rate sputtering apparatus with faced targets. The composition and crystal structure of the obtained films strongly depend on input power Ptand substrate temperature T2. The increase of Ptand Tslead to the reduction of oxygen content in the films. The films deposited at Ptabove 300 W and Tsof 200 °C exhibit a spinel type of crystal structure. Their lattice constant a0and resistivity &rgr; change monotonically from a0and &rgr; for &ggr;‐Fe2O3to those for Fe3O4with an increase of Ptfrom 300 to 800 W. On the other hand, when Ptis kept constant at 300 W, berthollide type of iron oxide films was deposited at Tsof 220–270 °C. The optical spectra of glow discharge reveal the existence of a large amount of ionic species such as H+and OH+in the space between targets. They seem to be effective for the formation of the berthollide type of iron oxide.

ISSN:0021-8979    

DOI:10.1063/1.330955

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Low‐temperature specific heat (Cp) and magnetic susceptibility (&khgr;) for the graphite intercalation compounds C6.2FeCl3(stage 1) and C17FeCl3and C11.3NiCl2.13(stage 2) is reported and analyzed. The FeCl3compounds show large anomalies in Cpat 4 and 1.7 K, respectively, while the NiCl2compound shows a peak at 20 K. For the FeCl3compounds, &khgr; is less than 5×10−6emu gm−1at all temperatures, showing only very small anomalies, while the NiCl2compound shows a very large peak in &khgr; at 16 K. Possible magnetic models for these layered compounds are considered, including a spin‐glass or spin‐cluster glass state.

ISSN:0021-8979    

DOI:10.1063/1.330956

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Large, thin‐film single domain areas have been observed, in the absence of a bias field, in garnets with magnetization perpendicular to the film plane.1,2The domain stability in the work by Krumme1was attributed to a combination of low saturation magnetization and a low Curie temperature. Uchishiba2relates the stability in his double layer system to appropriate anisotropy fields in one layer compared to the magnetization in the other layer. A more complete model for large domain stability in a bias field free environment is given in this work. Three distinct stability regimes are predicted by the model and all have been observed experimentally. Areas 3.5‐cm in diameter have been made into stable single domains. This was achieved in a material showing a zero bias strip width of 4.5 &mgr;m. The single domain diameter was, therefore, 7500 times the equilibrium energy domain width. The technique developed and the model have led to a new means for observing magnetic defects. More importantly, it also offers a means for measuring the strength of the defects. Possible applications of the model are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.330965

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The memory consists of a checkerboard pattern of transducers. Each transducer is connected to two lines of electrical conductors which form two grids of parallel lines. The grids are placed perpendicular to each other. A magnetic block is placed on top of each transducer. A magnetic field is applied to the system of magnetic blocks. It is slightly smaller than the coercive field H(c). One transducer generates a stress wave which will travel into the magnetic block adjacent to it. Its dipoles will line up parallel to the applied field if the stress is high enough. This corresponds to the writing process. If a stress wave interacts with a magnetic block which is magnetized antiparallel to the applied field, the block will reverse its magnetization direction. This leads to stress waves, which will induce a voltage in the transducer. No magnetic energy release and no generation of new stress waves is expected if the field is applied parallel to the magnetization direction of the block. This is the readout process.

ISSN:0021-8979    

DOI:10.1063/1.330957

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The crosstie‐Bloch line memory elements which were used in the serial crosstie memory can be reconfigured into a random access memory. The new approach decreases the access time, eliminates complexity, increases reliability, and is straightforward. The five‐level nonvolatile device is intended to be integrated on a silicon chip with decoders and drivers on the chip. It is expected that some of the five levels will be folded in with the levels used to connect the transistors needed for decoding and driving.

ISSN:0021-8979    

DOI:10.1063/1.330958

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We have investigated some of the problems involved in switching fast, high‐power pulses using single‐turn saturable core inductors constructed of Metglas 2605SC. These include hold‐off voltages and times, output pulse risetimes, B‐H curves of the material under fast pulse conditions, and propagation of the saturation field through the core. Experiments were done at Sandia on the RAMSES I accelerator which uses a 200‐kV Marx generator to provide a 200‐ns pulse to a 1 &OHgr; coaxial water transmission line.

ISSN:0021-8979    

DOI:10.1063/1.330960

出版商:AIP    

年代:1982

数据来源: AIP