This document discusses magnetic fluids and their properties. It introduces magnetic nanomaterials and magnetic colloids or ferrofluids, which are liquid suspensions of magnetic nanoparticles. Ferrofluids have properties that can be controlled by external magnetic fields. They are made up of magnetic particles dispersed in a carrier fluid with surfactants to prevent clumping. There are two main types: surfacted ferrofluids using molecules like oleic acid and ionic ferrofluids using electrically charged ferrite particles. Magnetic fluids have a variety of applications including in electronics, medicine, seat suspensions, and robotics due to their controllable properties in magnetic fields.

1. MAGNETIC FLUIDS
RAKESH K V
3rd Semester M.sc PHYSICS
CUSAT
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2. INTRODUCTION
Smart material
 Smart materials are materials that have multiple propertiess (chemical, electrical,
magnetic, mechanical and thermal)
 The properties of these materials can be significantly changed in a controlled
fashion by external stimuli
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3. Classification of the smart materials and their response
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4. Magnetic nanomaterials
At the nanolevel there is drastic change of properties for magnetic
materials
 They exhibit single domain characteristics, superparamagnetism
etc.
 Dependence of coercivity on particle size is important as they can
be used to distinguish whether the material are in single domain
or multidomain.
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5. Magnetic Colloids
 A Magnetic colloid also known as Ferrofluid is a colloidal suspensions
of single domain magnetic particles with a typical dimensions about
10nm dispersed in a carrier liquid
Properties can be controlled by external magnetic field
Ferrofluids are optically isotropic but in presence of an external
magnetic field exhibit induced birefringes
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6. Components of a magnetic fluid
Base fluid:It needed a base fluid,the choice of base fluid is based on
the field of application.eg; Water, Organic liquids
Single domain magnetic particles
Surfactants: It is used to prevent agglomeration.Common surfactants
are Oleic acid,Citric acid,tetramethylammonium hydroxide etc.
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7. Classification of Ferrofluids
Surfacted Ferrofluid
 Formed by magnetic particles(usually magnetite)
 Suitable surfactants are used ( Amphiphilic molecules such as oleic acid )
to prevent agglomeration
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8. Ionic Ferrofluid
Magnetic nanoparticles are electrically charged to keep the colloidal
system stable
Generally used magnetic particles are ferrites MFe2O4 (M=Mn,Zn,Cu )
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9. Stbility of colloids
D ≤ (72KBT/∏µ0M2)1/3
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10. Mechanisms of Rotation of magnetic moments
Ferromagnetic single domains in suspension can relax by one of two
methods
Brownian Relaxation with relaxation time
TB=3Vή/KBT
N´eel relaxation is caused by thermal fluctuations in the
magnetocrystalline anisotropy energy
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11. Normal field Instability
When a ferrofluid is subjected to a strong vertical magnetic field the
surface forms regular patterns of peaks and valleys
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12. Magneto Rheological Fluids
MR fluids are non colloidal suspensions of micro sized magnetisable
particles in an inert base fluid along with some addditives
In the absence of external magnetic field it behave like normal
Newtonian fluid
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13. Working modes of MR fluids
I. Valve mode
II. Shear mode
III. Squeeze mode
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14. Applications
Electronic devices
Medical fields
Seat suspensions
Robotics
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15. References
www.popsci.com/diy/article/2009-09/making-ferrofluids-work-you
https://www.teachengineering.org/.../uoh_nano_lesson02_activity2
https://en.wikipedia.org/wiki/Ferrofluid
https://science.nasa.gov/science-news/science-at.../23aug_mrfluids
www.intechopen.com/download/pdf/39980
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16. Thank You
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