- Superparamagnetism occurs in small ferromagnetic or ferrimagnetic nanoparticles and implies single-domain particle sizes of a few nanometers. The magnetic moments of individual atoms combine to form a giant magnetic moment for the nanoparticle as a whole. - Below the blocking temperature, nanoparticles behave superparamagnetically, with spontaneous fluctuations of the magnetization direction between θ=00 and θ=1800. Above the blocking temperature, nanoparticles behave paramagnetically. - Superparamagnetism allows applications in areas like drug delivery, hyperthermia cancer treatment, magnetic resonance imaging, and gene therapy by exploiting the magnetic properties at the nanoscale.

1. Few subjects are more difficult to understand than
magnetism.
Encyclopedia Britannica
Presented By-
R. UDAY KIRAN
Superparamagnetism and its
Biological Applications

2. Nanotechnology Plays by Different Rules
Normal scale Nanoscale

3. 3
Description of magnetic particles

4. MESOSCOPIC MAGNETISM
Classical Quantum
macroscale nanoscale
permanent
magnets
micron
particles
nanoparticles clusters molecular
clusters
Individual
spins
superparamagnetism
100 nm 10 nm 1 nm
S = 1023 1010 10 8 106 105 104 103 102 10 1
multi - domain single - domain Single molecule
nucleation, propagation and
annihilation of domain walls
uniform rotation quantum tunneling,
quantum interference
1
M/M S
0
-1
-40 -20 0 20 40
m0H(mT)
1
0
-1
-100 0 100
M/M S
m0H(mT)
1
0
-1
-1 0 1
M/M S
m0H(T)
Fe8
1K
0.1K
0.7K
Mn12-ac
Ferritin
size

5. Natural Nanomagnets:
•Ferritin
Man on average has 3-4 g of iron 30 mg per day are exchanged in plasma. Ferritin stores iron in mineral
form; Ferritins are found in animals, vegetables, mushrooms and bacteria
The internal core, 7 nm, may contain up to 4,000 iron(III) ions Approximately FeO(OH) Magnetism
depends on the number of ions Magnetic measurements provide information on the number of ions in
the core
•Magnetosomes
Nanomagnets embedded in cell membranes
•Magnetotactic bacteria iron core

6. Magnetism in reduced dimensions
Intrinsic properties
Finite-size effects
Surface effects
Interparticle interactions
Nanomagnetism
Size, aspect ratio
distribution

7. Magnetism in reduced dimensions
Surface effects
• lower coordination number
• broken magnetic exchange bonds
• frustrated magnetic interactions
• surface spin disorder
• reduced M in ferri-, antiferro-systems
• enhanced M in metallic ferro-systems
Surface and core magnetic orders
spin glass?
dead magnetic layer?
bulk-like?
• high-field
irreversibilities
• high saturation fields
• shifted hysteresis
loops

8. 8
Magnetic Moment vs. Cluster Size
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

9. Superparamagnetism
• Superparamagnetism (SPM) is a type of magnetism that occurs in
small ferromagnetic or ferrimagnetic nanoparticles.
• This implies sizes around a few nanometers to a couple of tenth of
nanometers, depending on the material.
• Additionally, these nanoparticles are single-domain particles.
• In a simple approximation, the total magnetic moment of the
nanoparticle can be regarded as one giant magnetic moment,
composed of all the individual magnetic moments of the atoms which
form the nanoparticle.

10. Superparamagnetism
For a magnetic particle the magnetic energy with uniaxial anisotropy is given
by
 2 E  KV sin
k T KV B 
Superparamagnetic relaxation is the spontaneous fluctuations of the
magnetization direction such that it alternately is near θ=00 and θ=1800.
The superparamagnetic relaxation time τ is given by

 

For particles with nanometric dimensions

 


KV
k T
B
exp 0  
where τ0 is of the order of 10-10-10-13 s, kB is the Boltzmann’s constant and T
is the temperature.

11. Superparamagnetism (SPM)
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation
τ – Average length of time that it takes for a ferromagnetic
cluster to randomly flip directions as a result of thermal
fluctuations
τ0 – Attempt period (characteristic of the material)
E – Anisotropic energy which is proportional to V
E=KV K is the anisotropy energy density constant

12. Superparamagnetism(SPM)
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation
Blocking temperature Tb E=KV=25kBTb
T>Tb τ < <τ0 Behave like Paramagnetic particle
T<Tb τ > >τ0 Magnetic ordering and open loops
If V↓ then τ ↓ SPM limit of hard drives
REF: IEEE Transaction on Magnetics Vol 33, No. 1(1997)978-983
An upper bound of about 36 Gbit/in.2

15. • What are the implications of such superparamagnetic states?
Without external magnetic field, the net moment is zero. As soon as
an external field is applied, the nanoparticles react similar to a
paramagnet (hence the “paramagnetism” in the name) with the one
exception that their magnetic susceptibility is much larger (hence the
“super” in the name).
• A word of clarification: Normally, any ferromagnetic or ferrimagnetic
material can behave paramagnetically. This is from a certain
temperature on and upwards, the so called Curie temperature Tc
• However, superparamagnetic behaviour is observed below the Cure
temperature and thus has to be explained differently.

16. New Properties of SPM
• Small size and larger magnetic moment for each particle like
Ferromagnetism --Large MS
• Response to external field like paramagnetic response---No open loop
• Superparamagnetic relaxation
τ=τ0exp(E / (kBT)) Neel-Arrhenius equation

19. Paramagnet, Ferromagnet &
Superparamagnet
Zero Magnetic Field Magnetic Field Applied
Paramagnet Domain moments align
randomly—no net
moment.
Net moment appears; the
applied magnetic field helps
the domains “find” each other
to become coupled.
Ferromagnet Domain moments coupled
(below Curie temp.) to
produce strong,
permanent moment.
Even higher magnetic moment.
Superparamagnet Domain moments that
would couple as in
Ferromagnet do not do so
because of small size—
boundary effect.
Domains “find” each other and
now it generates a moment
comparable to Ferromagnet.

20. Types of Magnetism

25. Application of Magnetic Nanoparticles in
Biomedicine
• Their size is comparable to the targeted entities.
• Nanoparticles can be magnetic. An external magnetic field gradient
can be applied to influence their movement. This way, they can
either deliver certain drugs or tag certain entities.
• Nanoparticles may also be resonantly excited. This allows heat
transfer to the surrounding tissue.

27. Radionuclide and Gene Delivery
• Radionuclide Delivery: An advantage of radionuclide therapy is that
the radionuclides do not have to decouple from the magnetic carriers.
The magnetic carriers can transport the radionuclides to the target
area where they can destroy the cancerous tissue. After the desired
result has been achieved, both the carriers and the radionuclides can
be directed out of the circulatory system.
• Gene Therapy: In gene therapies, the magnetic carriers are coated
with the therapeutical gene and transported to the target area.
Thanks to the possibilitiy of holding the gene and carrier at the target
for an extended time, the chances rise that the gene can get
transfected. Applications in this field of study are only in their
beginning

29. Ferrofluids:
Suppose some particles do have magnetic
moments.
N S N S N S N S
They will chain together!
The chain causes high viscosity.
 Magnetorheological effect.

30. Magnetorheological Effect

31. A magnetic fluid.

32. Just pretty.

34. Hyperthermia:
• Hyperthermia is usually an unwanted overheating of the body not to
be confused with common fever. In a hyperthermic state, the body
absorbes or produces more heat than it can dissipate. However,
hyperthermia can also be a wanted effect in order to destroy
tumorous cells and hence is sometimes created artificially.
• The magnetic particles first have to be brought to the target area,
where they can be caused to heat up by an AC magnetic field of
sufficient strength and frequency. The heat should exceed the
threshold of 42 degree Celsius and last for about 30 minutes in order
to properly destroy the tumour.

36. Mechanism of heating process
for MNPs Hyperthermia
1. Hysteresis loss
T T2 1
Applied field H(T)
Magnetization (emu/g)
Hysteresis loss at different temp.
Tc
2. Neel mechanism
Rotation of the magnetization
vector within the particles.
3. Brownian Mechanism
Mechanical rotation
of the magnetic particle
Intrinsic superparamagnetism
(the particle magnetic moments aligns with
external field)
Extrinsic superparamagnetism
(the particle itself aligns with
field)
H

37. Magnetic relaxation mechanisms
H=0 H ≠ 0
H=0
Néel relaxation
H = 0
Brownian relaxation

40. Drug Delivery
The advantages of targeted drug delivery seem numerous:
Most drugs are non-specific, i.e. they get distributed over the
whole body as soon as they get administered intravenously.
Targeted delivery can ensure that only specific areas get
influenced by the (otherwise harmful) drugs and as little as possible
of the drug needs to be administered. This method seems especially
applicable, when the drug is very damaging to healthy tissue.
Fields of application:
• Chemotherapy,
• radionuclide therapy,
• arthritis or
• gene therapy.

43. Gene Delivery
• FeOfection is a solution of nanoparticles with an iron oxide core.
Att tillföra en ny gen i en cell
•The core is stable and the magnetic properties can be used e.g. in tracking of cells with MRI.
• The surface of the particles are modified to promote binding of DNA to the particles and facilitate
transport of the resulting particle/DNA complexes into cells.
• FeOfection can be used for both transient (temporary expression) and stable (incorporated in the
genome) transfection.

44. Imaging using magnetic nanoparticles
Marknaden drivs av ett medicinskt behov av effektivare och känsligare diagnostik

45. FeOdots incubated with cells and exposed to a magnetic field
Iron Oxide
Phospholipid
Amino-PEG
NHS-Alexa 647
Iron Oxide
U-2 OS cell incubated with Alexa-647 magnetic nanoparticles for
1 hour

46. Imaging - Regenerative medicine
Stamceller märks med Genovis magnetiska nanopartiklar ex vivo och injeceras i mus
T2* Map Prussian blue positive
cells at edge of tumor
C6 glioma
FeOlabeled cells were
injected i.v. in C6 glioma in
mouse flank 14 days prior to
3T MRI
Cells labeled with FeOlabel can easily be
visualised with MRI.
Mesenchymal stem cells were labeled with
FeOlabel and then injected into a mouse
with a C6 glioma. After 14 days the cells are
visible with MRI. Particles can also be
visualised by Prussian Blue iron staining.

47. Opportunities in Nanomagnetism
Challenges in
Nanomagnetism
100% spin-polarized
materials
Magnetic
logic
Instant boot-up
computer
Nano-bio
Mag-sensors
RT magnetic
semiconductors
Spin-transistor
with gain
Ultra-strong
Permanent
Magnets
Ultra
High density
media

48. Superparamagnetism
Superparamagnetism
paramagnetism below Curie’s temperature
large susceptibility
superparamagnetism limit
Origin of superparamagnetism
magnetism: result of spin alignment
thermal excitation, ferromagnetism <-> paramagnetism
small scale, below Tc:
thermal excitation destroys the ordering between the clusters
thermal excitation cannot upset alignment within the cluster
ferro~ inside & para~ outside => treated as a large spin as a whole
Experiment results
stepped hysteresis can be found below certain temperature.
frequency dependent AC susceptibility

49. 49

50. 50

51. 51