摘要:

A model of properties of colloidal dispersions of fine paramagnetic particles has been investigated. The model has been used to investigate the effects of large magnetic fields on the short‐range order within the dispersions. The onset of significant short‐range order at a well‐defined critical field has been found, in agreement with previous experimental work.

ISSN:0021-8979    

DOI:10.1063/1.334582

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In this work, a newly developed ferrofluid was used for studying recorded data patterns on high‐performance rigid discs where densities exceed 10 000 frpi. It has been found that ferrofluids must exhibit certain properties to be useful in this application. Fluid properties such as particle size distribution, concentration and stability are described as they relate to optical (microscopic) resolution of the magnetic pattern. The application of this new water based ferrofluid for single‐bit defect detection is also discussed in conjunction with a novel method which was developed for this use.

ISSN:0021-8979    

DOI:10.1063/1.334583

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Agglomeration of &ggr;‐Fe2O3acicular magnetic particles in concentrations of approximately 0.005% by weight in water was studied by measuring light transmission through the dispersions while they were subjected to a stepwise rotating magnetic field of 15‐Oe magnitude. Transmitted light intensity varies synchronously with rotation, having its minimum when particles are aligned with their long axes parallel to the light and its maximum when particles are perpendicular to the beam. With time, the minimum light level diminishes, whereas the maximum light condition remains constant. This behavior is attributed to the formation and growth of particle chains. The chaining idea is supported by the observation that the response time of particles to the changing field increases with time and by other optical effects which are observed in high‐speed rotation of the field. The effect of milling time on particle mobility is also observed. The observations are discussed in terms of a model of the attraction and attachment behavior of dilutely dispersed magnetic particles in a fluid.

ISSN:0021-8979    

DOI:10.1063/1.334584

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Particle size effects on magnetic properties of BaFe12−2xTixCoxO19fine particles were investigated. Saturation magnetization of these particles decreased with decreasing particle size. This result can be explained with the existence of a nonmagnetic thin layer, several angstroms in thickness, on the surface of the particles. Particle size dependence of coercivity for these particles, below 1000 A˚ in size, follows the superparamagnetism theory. For the decrease in coercivity above 2000 A˚, multidomain nucleation is inferred as one of the possible mechanisms. Particle shape dependence of coercivity is well explained with the coherent rotation model, considering shape anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.334585

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Granular films consisting of finely dispersed Fe2O3grains in an Al2O3matrix have been studied by means of Mo¨ssbauer spectroscopy and magnetization measurements. The temperature dependence of the relaxation time is coherent with the superparamagnetism model only if in the &tgr;0calculation, the noncompensated moment of the antiferromagnetic particles, is considered. This moment is proportional to (n)1/2,nbeing the number of magnetic atoms in the particle.

ISSN:0021-8979    

DOI:10.1063/1.334586

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A small‐scale experimental facility for studying the magnetic filtration of submicroscopic particles through a bed of packed spheres is described. The experimental parameters are the particle size and concentration, solution pH, flow rate, magnetic field, filter characteristics, and time. Some results for aqueous solutions containing submicron &agr;‐Fe2O3spherical particles are presented, and discussed from the viewpoint of recent theoretical studies.

ISSN:0021-8979    

DOI:10.1063/1.334587

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The influence of interparticle double‐layer and dipole‐dipole forces on the buildup of ultrafine colloidal particles around a magnetized collection center in a static colloid is considered. Expressions are given and developed, respectively, that describe the double layer and dipole‐dipole interparticle effects in a one‐dimensional particle number gradient. These expressions lend themselves to a description of the effects by a double‐layer diffusion and a dipole‐dipole flocculation coefficient. The size of these coefficients and of the normal thermal diffusion coefficient is compared over a wide range of colloidal particle radius, and ranges of radius are identified in which each coefficient can be dominant. Steady‐state solutions of the transport equation including these coefficients are computed and show that this inclusion can be justified, and is indeed necessary, for significant ranges of particle radius.

ISSN:0021-8979    

DOI:10.1063/1.334588

出版商:AIP    

年代:1985

数据来源: AIP