magnetic properties of materials.pptx

8/11/2019 Magnetic properties of materials.pptx

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MAGNETIC PROPERTIES OF

MATERIALS

Jesus Romo

1649886


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Early days

MAXWELL EQUATIONS


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Maxwell Equations


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The magnetic parameters Force exerted by the magnetic field, H, is:

F = V

= Susceptibility, how responsive a material is to and applied magnetic field.

Magnetic field in a selenoid:

H = The magnetic field strength within a material is known as magnetic induction or magnetic flux density

B=H

Energy in a magnetized system

E = MB

Permeability of the free space = 1.257 x10-6 H/m

= 1 + , permeability

Magnetization Magnetic dipole Moment

M= /V = AI


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Quantum Numbers

NEnergy Level

LAngular Momentum

MMagnetic Momentum

SSpin Magnetic Number


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Bohrsmagneton

The magnetic moment is then,

We can expressin terms of the angular momentum L of theelectron.

For electrons in atoms, angular momentum is quantized. It'scomponent in a particular direction is an integral multiple of:

If

then, = eh/4m is called the Bohr magneton and denoted It'snumerical value is

Magnetic momentum

quantified!


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Diamagnetism

All elements with filled shellsCu, Ag, Au.

Small and negative susceptibility.


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Paramagnetism

Small and positive susceptibility to magnetic fields. Slightly attracted by a

magnetic field and the material does not retain the magnetic properties when

the external field is removed.

Paramagnetic materialsmagnesium, molybdenum, lithium, and tantalum


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Ferrimagnetism

Residual magnetization


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Superparamagnetism

No coercivity neither remanensce!

Single domain

and multiple domain


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Applications


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At present

Spintronics!

In the absence of a magnetic field, spin up and spin down

have the same energy for a free electron. The statevariables for a switch then requires the presence of a

magnetic field.


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Spintronics

IMPROVED MAGNETIC RECORDING MEDIA!

Nobel Prize 2007Albert Fert, Giant magnetoresistance(GMR) was discovered with layered systems of

ferromagnetic and antiferromagnetic materials of

nanometer size by Fert and Grnberg in 1988.


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Spintronics

Magnetoresistance; the change in the resistance of a

material in the presence of a magnetic field:

Giant Magnetoresistance (GMR) was discovered withlayered systems of ferromagnetic and antiferromagnetic

materials of nanometer size by Fert and Grnberg in

1988, for which they won the 2007 Nobel prize in physics.

The physical origin is due to the diference in the electron

scattering (i.e., the resistance) for electron spins oriented

diferently with respect to the magnetization.


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Magnetic Nanowires

Applications (biological): magnetic separation, biosensing,

drug delivery, cellular probes.

Structural impact: spherical geometry constrain property

engineering. Instead use multisegmented nanoparticles.

Chemical properties: composition, surface

functionalization.

Physical properties: size, shape, composition.

Large, tunable magnetic moments.


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Magnetic Recording Process


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Discussion & Questions

magnetic properties of materials.pptx

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