Can be defines as:Phenomenon by which materials assert an attractive or repulsive force or influence on other materials

Magnetic Materials includes -iron, some steels, lodestone minerals

Principle applied in medicine- Magnetic Resonance Imaging

From:http://en.wikipedia.org/wiki/Image:Modern_3T_MRI.JPG

MAGNETISM

Magnetism force moving electrically charged particles Magnetic dipoles is similar to electric dipoles Represented by small bar of magnet with north and south poles (also represented by arrow)Within magnetic field, the force of the field exerts a torque that tends to orient the dipoles with the field

Magnetic Dipoles

A

I

m

un

From Principles of Electronic Materials and Devices, Second Edition, S.O. Kasap (© McGraw-Hill, 2002)http://Materials.Usask.Ca

Fig. 8.1: Definition of a magnetic dipole moment.

Magnetic Dipole Moment, μMagnetic Dipole Moment, μmm

nm IAuI = circulating currentun= unit vector coming out

from area A

B

A

I

B

m

From Principles of Electronic Materials and Devices, Second Edition, S.O. Kasap (© McGraw-Hill, 2002)http://Materials.Usask.Ca

Fig. 8.2: A magnetic dipole moment in an external fieldexperiences a torque.

BrO P

µ m NS

µ m

F ig. 8 .3 : A m agnetic dip ole m om ent p uts out a m agneticfield jus t like b ar m agnet. T he field B dep ends on µm .

From Principles of Electronic Materials and Devices, Second Edition, S.O. Kasap (© McGraw-Hill, 2002)http://Materials.Usask.Ca

Origin of Magnetic Moments

Each electron in an atom has magnetic moments that originate from two sources:•One is related to its orbital motion around the nucleus; as amoving charge, electron

-small current loop, -generating a very small magnetic field, -have a magnetic moment along its axis of rotation•The other magnetic moment originates from this electron spin, which is directed along the spin axis

Spin magnetic moments may be only in an “up” direction or in an antiparallel “down” direction

Do you know?Magnetic resonance (MR) imaging is founded on the manipulation of magnetic dipole moments in such a way that signals generated from these interactions that can be translated into visual images of the body.

Figure Typical MR images of the head (left), neck (middle) and kidneys (right).

Magnetic Field Vectors

Magnetic Field Vectors

•Magnetic Field Strength, H

•Magnetic Flux Density, B

•Magnetic Permeability,

•Magnetization, M

•Magnetic Susceptibility, χm

• The externally applied magnetic field, i.e. the magnetic field strength, H.

Magnetic Field Strength

If the magnetic field is generated by solenoid consistingof:N= closely spaced turns, l =length, I= current magnitude

The units of H are amperes per meter.

Magnetic Flux Density

Magnetic flux density, B, represents themagnitude of the internal field strength within a substance that is subjected to an H field.

Both B & H are field vectors, being characterized not only by magnitude, but also by direction in space.

The magnetic field strength and flux density are related according to:

The units for The units for B B are teslasare teslas

Magnetic PermeabilityMagnetic Permeability

HB

Magnetic permeability is define as the magnetic field per unit magnetizing field

The permeability has dimensions of webers per amperemeter (Wb/A-m) or henries per meter (H/m).

In a vacuum,

where o is the permeability of a vacuum, 4 10-7 (1.257 10-6) H/m.

Relative permeability μr of a medium is the fractional increase in the magnetic field with respect to the field in free space when a material medium is introduced.

H

B

B

Br

00

Magnetic PermeabilityMagnetic Permeability

Magnetization

Another field quantity, M, called the magnetization of the solid, is defined by the expression

In the presence of an H field, the magnetic moments within a material tend to become aligned with the field & to reinforce it by virtue of their magnetic fields; the term oM

The magnitude of M is proportional to the applied field as follows:

Magnetic SusceptibilityMagnetic Susceptibility

HMm

Magnetic susceptibility χm indicates the ease with which the material becomes magnetized under an applied magnetic field

m is unitless

Represented by:B = Bohr Magneton = 9.27 x 10-24 A m2

•Bohr magneton (B ) is a useful elementary unit of magnetic moment on the atomic scale. It is equal to the magnetic moment of one electron spin along an applied magnetic field B =eħ/2me

Bohr MagnetonBohr Magneton

ee is the elementary charge is the elementary charge is the reduced Planck’s constant is the reduced Planck’s constant mmee is the electron rest mass is the electron rest mass

Diamagnetism = a form of magnetism that is non-permanent and occurs only in ta form of magnetism that is non-permanent and occurs only in the applied field with the direction he applied field with the direction opposite opposite the applied field the applied field

Note:r < 1 (slightly) : m is negative and in the order of 10-5

Paramagnetism = magnetism does not exist with absence of H (random arrangemmagnetism does not exist with absence of H (random arrangement of dipoles moments), but exist under applied field (H)ent of dipoles moments), but exist under applied field (H)

Note: r > 1 : m is small and positive in the order of 10-5 to 10-2

Diamagnetic and Paramagnetic materials “non-magnetic”

Diamagnetism and Paramagnetism

B vs H for diamagnetic and paramagnetic materials

Diamagnetism : Paramagnetism : Ferromagnetism

Diamagnetics Paramagnetics

Material m Material m

Aluminum Oxide

Copper

Gold

Mercury

Silicon

Silver

Sodium Chloride

Zinc

-1.81x10-5

-0.96x10-5

-3.44x10-5

-2.85x10-5

-0.41x10-5

-2.38x10-5

-1.41x10-5

-1.56x10-5

Aluminum

Chromium

Chromium Chloride

Manganese Sulfate

Molybdenum

Sodium

Titanium

Zirconium

2.07x10-5

3.13x10-4

1..51x10-3

3.70x10-3

1.19x10-4

8.48x10-6

1.81x10-4

1.09x10-4

Room Temperature m for Diamagnetic and Paramagnetic Materials

Diamagnetism and Paramagnetism

Ferromagnetism = phenomenon in certain (metallic) materials that possess a permanent magnetic moment in the absence of H

Domain = Area (volume) of a material that the mutual spin alignment exist Saturation Magnetization (Ms) The maximum possible magnetization

Ferromagnetism

Antiferromagnetism = the alignment of the spin moments of the neighboring atoms or ions in exactly opposite direction

MnO = Antiferroelectric Mn2+ Spin-origin magnetic moment Align antiparallel in crystal structure

O2- No net magnetic moment Cancellation of ms, ml

Antiferromagnetism and Ferrimagnetism

Ferrimagnetism = a permanent magnetization in materials that is very similar to ferromagnetism but originates from different source of the net magnetic moment

Ferrimagnetic Material : Cubic Ferrites : MFe2O4 : M = one of the metallic elements Prototype Fe3O4 (magnetite or lodestone) Inverse Spinel Structure

Fe2+ O2- - (Fe3+)2 (O2-)3 O2- = Magnetically neutral

Fe2+ = Net spin magnetic moment = 4B Fe3+ = Net spin magnetic moment = 5B

Antiferromagnetism and Ferrimagnetism

FerrofluidFerrofluid• Ferrofluids or Magnetic Fluids are fluids with

magnetic nanoparticle suspended in a liquid medium

• The particles are generally coated to prevent magnetostatic interactions which would cause the particles to cluster together

From-http://www.ucl.ac.uk/~ucfbpmb/ferrofluid%20copy.jpg

Biomedical Applications of Biomedical Applications of Magnetic MaterialsMagnetic Materials

• Abnormalities in body tissues and organs can be detected on the basis of the production of cross-sectional images using Magnetic Resonance Imaging (MRI)

• Chemical analysis of body tissues is also possible Chemical analysis of body tissues is also possible using Magnetic Resonance Spectroscopy (MRS).using Magnetic Resonance Spectroscopy (MRS).

• Magnetic Drug Targeting- applies nanoparticles to Magnetic Drug Targeting- applies nanoparticles to target drugs and genes to specific sites in vivotarget drugs and genes to specific sites in vivo– Using this method, this can enhance drug and gene Using this method, this can enhance drug and gene

uptake at the sitesuptake at the sites– Also known as magnetic target carriers (MTC)Also known as magnetic target carriers (MTC)

A chitosan "mothership" capsule (light blue) attaches and delivers drug-filled vesicles (dark blue) to a tumor. This capsule may be targeted to tumor cells either by antibodies (the Y- shaped spines) on its outer surface or by magnetic nanoparticles (dark red) inside. These two targeting systems effectively act as navigators, taking the capsules "along for the ride" to precise locations where the drugs are needed. Dowling et al. has found, they can then be guided to specific locations in the body with an electromagnetic field. 

www.bioe.umd.edu/fischell-fellowship/dowling.html

Magnetic force bioreactor for tissue engineering

• The magnetic force bioreactor is designed to apply forces directly to the cell membrane by coupling biocompatible magnetic nano- and microparticles to the membrane surface

From-http://www.maths.nottingham.ac.uk/personal/pmzsjf/Image2.gif

Other applications:

•MRI Contrast Enhancement

•MR delivers excellent soft-tissue contrast, however, assistance from contrast media (which usually from paramagnetic agent) is done to obtain better image.

Figure shows brain images both before and after contrast allow disruptions in the blood-brain barrier to be investigated

From: www.hull.ac.uk/mri/lectures/gpl_page.html