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Rheomagnetic measurements on suspensions of magnetic recording particles (1992)

Kwon, T. M. ; Jhon, M. S. ; Karis, T. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 3770-3777

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Measurement of magnetic particle flow orientation properties is of considerable practical and fundamental interest as it relates to the particulate recording tape and disk manufacturing industry. For production of high-quality magnetic tapes and disks, the suspension must be well dispersed. Previous study focused on rodlike single-domain magnetic particles for longitudinal magnetic recording. In contrast, platelike particles are considered here for use in perpendicular recording. Both theory and experiment have demonstrated that a magnetic sensing technique employed to measure the hydrodynamic orientation provides a measure of the flocculation state for rodlike magnetic particle suspensions. Here the previous theory is extended and new experimental results are shown to demonstrate that the hydrodynamic orientation measurement apparatus can also be used to measure the flocculation state of platelike particles. The key new experimental result is the contrast between the flow orientation properties of the rod versus the platelike particles. Rodlike single-domain particles orient parallel to the flow direction causing the suspension magnetic permeability parallel to the flow direction to decrease with increasing flow rate. In the case of the platelike Ba-ferrite particles, the opposite behavior is observed. As the flow rate is increased, the particles orient with their flat side parallel to the flow direction causing the suspension magnetic permeability parallel to the flow direction to increase.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.352272

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Effects of shear rate and particle concentration on rheological properties of magnetic particle suspensions (2000)

Choi, H. J. ; Kwon, T. M. ; Jhon, M. S.

Springer

Journal of materials science 35 (2000), S. 889-894

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Rheological characterizations were made for various types of magnetic particles (rod-like γ-Fe2O3, CrO2, and plate-like Ba-ferrite) and nonmagnetic (rod-like α-Fe2O3) suspensions, in terms of particle concentration and shear rate. Shear rate dependence on viscosity was accurately described by the Casson equation. The highest yield stress for Ba-ferrite among the four types of particles represents the sensitive flocculation characteristics of Ba-ferrite with respect to concentration. The effect of non-magnetic α-Fe2O3 and magnetic γ-Fe2O3 particle mixtures on suspension viscosity was also examined, and a negative deviation from the tie line of individual particle viscosities was observed.