A quick reference for knowing the properties of Magnetism and a brief note on Superparamagnetism

1. Properties of Magnetism
RIJU CHANDRAN.R
NCNSNT,UNOM

2. MAGNETISATION (M)
• Magnetisation of a material is defined as the magnetic dipole
moment induced per unit volume of the material.
• The unit of magnetisation is Amperes/meter.
• If ‘m’ be the magnetic dipole moment of a specimen of volume
‘v’ we can say that M = m/v.
• On an unmagnetized matter M will be 0 and when a matter is
magnetized each atomic magnetic dipole will point in the same
direction and M will be constant throughout

3. MAGNETIC INDUCTION (B)
• It is a process by which a substance, becomes
magnetized by a magnetic field, i.e the induced
magnetism is produced by the force of the field
radiating from the poles of a magnet.
• It is also called magnetic flux density, a vector
quantity used as a measure of the strength of a
magnetic field.
• The unit of magnetic induction is weber/m2.

4. MAGNETIC FIELD INTENSITY(H)
• It is used to characterize the strength of an external
field i.e. the magnetic field due to the external
sources (electric current) only, excluding the
contribution due to material’s internal magnetic field.
• It is also known as Magnetizing force or Auxiliary
Magnetic field.
• Its unit is same as that of Magnetisation i.e
Amperes/meter

5. MAGNETIC SUSCEPTIBILITY (Xm)
• It is defined as the ratio of the magnetisation(M) to
the magnetic field intensity (H)
• Xm = M/H
• The magnetic susceptibility of a material is defined
as the intensity of magnetisation acquired by the
material for unit field strength.

6. MAGNETIC PERMEABILITY (µ)
• Magnetic permeability of a medium is defined as the
ratio of magnetic induction to the intensity of the
magnetising field.
• µ =B/H

11. DIAMAGNETISM
 It occurs in those substances whose atoms consist of an
even number of electrons,thus the electrons of such atoms
are paired.
 Electrons in each pair have orbital motions as well as spin
motions.
 Magnetic dipole moment of the atom is zero.
 In diamagnetism the electron moving in a direction so as to
produce a magnetic field in the same direction as the
external field applied, thus it acquired an effective
magnetic dipole moment which is opposite to the applied
field.

12. Properties of Diamagnetic material
The susceptibility(Xm) of a diamagnetic material has a
low negative value.It is independent of temperature.
In an external magnetic field, they get magnetised in a
direction opposite to the field and they have a tendency to
move away from the field.
If suspended freely, they set themselves perpendicular to
the field.
Eg: Pb,Au,Ag,Zn,Bi,Sb etc

13. PARAMAGNETISM
 In paramagnetic material,the magnetic field associated
with the orbiting and spinning electrons do not cancel out
 The molecules in paramagnets behave like little magnets
 When an external field is applied it will turn and line up
with its axis parallel to the external field.
 The diamagnetic force of repulsion is also present here
but it is not so strong.
 When a paramagnetic substance is heated the thermal
agitation of its atom increases then the alignment of
dipoles become more difficult,that’s why the
magnetization of paramagnetic substance decreases as
the temperature of the substance increases.

14. Properties of Paramagnetic material
 These substances have relative permeability µr > 1 and
Xm is positive,the susceptibility decreases with rise in
temperature.
 In an external magnetic field, these substances get
magnetised in the direction of the field.Hence they move
from weaker to stronger part of the external field.
 If suspended freely,they set themselves parallel to the
field.
 Eg: Al,Cr,Mn,CuSo4,liquid oxygen and solutions of salts
of iron and nickel.

15. FERROMAGNETISM
• Ferromagnetic substances are very strongly magnetic.
• A ferromagnet has a spontaneous magnetic moment.
• Due to spin of electrons they have a net intrinsic magnetic
dipole moment.
• The interaction between the neighbouring atomic
magnetic dipoles is very strong,it is known as spin
exchange interaction and is present even in the absence
of an external magnetic field.
• All magnetic moments within a domain will point in the
same direction resulting in a large magnetic moment.
• When a ferromagnetic material is heated to a very high
temperature, the thermal vibrations may become strong
enough to offset the alignment within a domain and the
material loses its ferromagnetic property and behaves like

16. Paramagnetic material.The critical temperature above
which a ferromagnetic material becomes a paramagnetic is
called Curie temperature.

17. Properties of ferromagnetic material
 The value of µr and Xm of these materials are very large.
 They get strongly magnetised in the direction of the
external field and so they are strongly attracted by
magnets.
 They set themselves parallel to external field if suspended
freely.
 These materials exhibited the phenomenon of Hysteresis
 As temperature increases the value of Xm
decreases.Above a certain temperature known as curie
temperature ferromagnets become paramagnet.
 Eg: Fe,Ni,Co etc

18. SUPERPARAMAGNETISM
 Ferromagnetic particles become unstable when the
particle size is reduces below a certain size,since the
surface energy provides a sufficient energy for domains
to spontaneously switch polarization directions then
ferromagnets becomes paramagnetic.
 In nanometer sized ferromagnetic turned to
paramagnetic it behaves differently from the
conventional paramagnetic and is referred to as
superparamagnetic.
 Superparamagnetism was first predicted to exit in small
ferromagnetic particles below a critical size by Frankel
and Dorfman.

19. • The first example of superparamagnetic property was
reported in literature as early as 1954 on nickel particles
dispersed in silica matrix.
• An operation definition of superparamagnetism would
include two requirements :
1. The magnetization curve must show no hysteriasis,
since that is not a thermal equilibrium property.
2. The magnetization curve for an isotropic sample must be
temperature dependent to the extent that curves taken
at different temperatures must approximately
superimposed when plotted against H/T after correction
for the temperature dependence of the spontaneous
magnetization.

20. APPLICATIONS
• BIOMEDICAL APPLICATIONS :
 Detection: MRI Magnetic Resonance Imaging
 Separation: Cell-, DNA-, protein- separation, RNA
fishing
 Treatment: Drug delivery, hyperthermia,
magnetofaction
• OTHER APPLICATIONS :
 Sensors: high sensitivity (GMR, BARCIII)
 Ferrofluid: Tunable viscosity, Stealth aircraft.

21. THANK YOU..