Absence of anisotropy effects in the magnetization of ferrofluids

Journal Article · Fri Nov 30 23:00:00 EST 1979 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.325956· OSTI ID:5628384

Krueger, D A

Existing magnetization measurements on magnetic colloids known as ferrofluids have been analyzed using the Langevin theory for spherical particles with no anisotropy energy. Deviations from simple Langevin theory are interpreted as being a reflection of a distribution of particle sizes. We consider the more general situation of ellipsoidal particles with a general anisotropy energy which depends only upon the relative orientation of the magnetic moment and the particle. By assuming that the orientation of the particle is in thermodynamic equilibrium, we show that the anisotropy has no effect on the magnetization of the colloid and that the Langevin theory obtains. Physically this result can be thought of as follows. The magnetic field tends to align the magnetic moment along that field. The anisotropy energy, E/sub a/, then favors aligning the easy axis of the particle along that moment and this second alignment has no effect on the moment.

• Research Organization: Sandia Laboratories, Albuquerque, New Mexico 87185
• OSTI ID: 5628384
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 50:12; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

657007* -- Electricity & Magnetism-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
COLLOIDS
CONFIGURATION
DISPERSIONS
ELLIPTICAL CONFIGURATION
EQUATIONS
LANGEVIN EQUATION
MAGNETIC MATERIALS
MAGNETIC MOMENTS
MAGNETIZATION
MATHEMATICAL MODELS
ORIENTATION
PARTICLES
SIZE
THERMODYNAMICS