niarchos 130705 [read-only] - demokritosoldportal.demokritos.gr/parousiaseis/niarchos_130705.pdf ·...

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• ∆ΟΜΗ ΟΜΙΛΙΑΣ• Η µαγνητική ροπή του ηλετρονίου και του ατόµου• Η µαγνητική ροπή πολλών ατόµων• Κατηγορίες µαγνητιkών υλικών• Από τους νανοµαγνήτες στους γνωστούς µαγνήτες• Εφαρµογές µαγνητικών υλικών• - Μαγνητική εγγραφή• - Αισθητήρες• - Ιατρικές Εφαρµογές Magnetic Hyperthermia• - Bιοιατρικές Εφαρµογές• - ∆ιαστηµικές εφαρµογές• Μαγνητοηλεκτρικά- σπιν τρανζίστορ

∆ρ. ∆. ΝιάρχοςIνστιτούτο Επιστήµης ΥλικώνΕΚΕΦΕ «∆ΗΜΟΚΡΙΤΟΣ»

“ΜΑΓΝΗΤΙΚΑ ΥΛΙΚΑ ΚΑΙ ΥΨΗΛΗ ΤΕΧΝΟΛΟΓΙΑ:Από τη µαγνητική ροπή του ηλεκτρονίου σε εφαρµογές καθηµερινές και µελλοντικές

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VARIOUS SCALES

nmµm

mm m

Å

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Discovering Magnetism

Supposedly, about 4,000 years ago in Minor Asia a shepardnamed Magnes discovered magnetism when the nails in his shoes stuck to a rock. This was because of the iron deposits in the rock. He called the rock magnetite, but it was never decided if he named it after himself or after the town he came from, Magnesia.

By A.D. 1200, Chinese and European sailors used magnetic compasses to steer their ships.

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Gilbert’s Discovery

1600- William Gilbert published a book called "De Magnete" which became the standard one in Europe for electrical and magnetic phenomena.

Magnus magnes ipse est globusterrestris.

[The whole Earth is a magnet.]

William Gilbert

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A Magnetic Perpetual Motion Machine

The US patent office was issuing patents for magnetic perpetual motion machines as late as the 1970's.

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Scale of Magnet Field650 T The Strongest Destructive Pulsed Magnet

60 T long pulse magnet

33 T continuous field magnet

2 T MRI machine

0.4 T stereo speaker magnets

0.4 T lodestone/magnetite (Fe3O4)

0.3T house refrigerator magnets

3*10-5 T Surface of earth

3*10-10 T produced by human body

1 Tesla = 104 Oe

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Uses of Magnetism

Magnetic Cranes

Computer HardDrive

Motors used in Cars, Airplanes and everywhere

Magnetic levitation Train

Etc. etc……

MRI

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ΜΑΓΝΗΤΙΚΑ ΥΛΙΚΑ ΚΑΙ ΥΨΗΛΗ ΤΕΧΝΟΛΟΓΙΑ:Από τη µαγνητική ροπή του ηλεκτρονίου σε εφαρµογές καθηµερινές και µελλοντικές

VARIOUS MAGNETIC FIELDS

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Atomic Structure to X-Rays 16

Electrons

Nucleus

Orbit / Energy Level

The Bohr Atom

Atomic Spectra and Bohr Model

2. But a charged particle moving in an electric field should emit energy.

+Electronorbit

One view of atomic structure in early 20th century was that an electron (e-) traveled about the nucleus in an orbit.

1. Classically any orbit should bepossible and so is any energy.

End result should be destruction!End result should be destruction!

Atomic Spectra and Bohr Model

2. But a charged particle moving in an electric field should emit energy.

+Electronorbit

One view of atomic structure in early 20th century was that an electron (e-) traveled about the nucleus in an orbit.

1. Classically any orbit should bepossible and so is any energy.

End result should be destruction!End result should be destruction!

Energy of state = - C/n2 where C is a CONSTANTn = QUANTUM NUMBER, n = 1, 2, 3, 4, ....

• Bohr said classical view is wrong. • Need a new theory — now called QUANTUM

or WAVE MECHANICS.• e- can only exist in certain discrete orbits

— called stationary states. • e- is restricted to QUANTIZED energy states.

Atomic Spectra and Bohr Model (2)

Energy of state = - C/n2 where C is a CONSTANTn = QUANTUM NUMBER, n = 1, 2, 3, 4, ....

• Bohr said classical view is wrong. • Need a new theory — now called QUANTUM

or WAVE MECHANICS.• e- can only exist in certain discrete orbits

— called stationary states. • e- is restricted to QUANTIZED energy states.

Atomic Spectra and Bohr Model (2)


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Atomic Structure to X-Rays 3

Discovery of the Electron• Cathode Rays

• In 1897 J.J. Thompson proposed the rather startling hypothesis that cathode rays were streams of negatively charged particles – electrons.

-ve cathode +ve anode

Red Hot – Energy Transfer

THE ELECTRON and ITS PROPERTIES

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SPIN ROTATION: S

“ORIGIN OF MAGNETIC MOMENTς”

Magnetic moment originates from the motion of electrons

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Lecture 22Lecture 22--22 Electron as Source of Magnetism in Atoms

• Orbital angular momentum of an electron

( ) ( )2

2 2 2l ee e

v e qe r rm v Lr m m

µ ππ

⎛ ⎞= − ⋅ = − =⎜ ⎟⎝ ⎠

ur

orbital angular Momentum quantized as integer times h

Bohr magneton

• Spin angular momentum of an electron

2Se e

e ehSm m

µ ≈ − = ±

electron spin ±½h

h 341.05 10 ( )2h J sπ

−= ≅ × ⋅

Planck’s constant

U Bµ= −ur urin external B field

2l Bem

nehnµ µ⋅ = −= −

249.27 10 ( / )B J Tµ −≅ ×

2

Dipole Moments in Atoms

In the classical picture of atoms, the electrons orbit the nuclei, and they also spin on their axes. Both of these effects produce current loops, and these current loops in turn produce magnetic dipole moments.

Orbital magnetic moment Spin magnetic moment

ORIGIN OF MAGNETISM IN ATOMS

Total Moment = µl + µs

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STERN GERLACH EXPERIMENT- QUANTIZATION of SPIN

J=S=1/2

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FROM ATOMS to SOLIDS

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ATOMS in EXTERNAL FIELDS-QUANTIZATION

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PAULI PRINCIPLE- 3d metals electronic configuration

Ions Spin direction of 3d orbitals # electrons Mag. Moment

Ti3+ , V4+ 1 1 µΒ

Ti2+ , V3+ 2 2 µΒ

V2+, Cr3+, Mn4+ 3 3 µΒ

Cr2+ , Mn3+ 4 4 µΒ

Mn2+, Fe3+ 5 5 µΒ

Fe2+, Co3+ 6 4 µΒ

Co2+ 7 3 µΒ

Ni2+ 8 2 µΒ

Cu2+ 9 1 µΒ

Zn2+, Cu+ 10 0 µΒ

Principle quantum number n = 1, 2, 3,….. describes orbital size and energy

Angular momentum quantum numberl = 0 to n-1 describes orbital shape

Magnetic quantum number ml = l, l-1…-l describes orientation in space

of the orbital relative to the other orbitals in the atom

Spin quantum number ms = +1/2 or -1/2 describes the direction of spin

of the e- on its axis

Pauli Exclusion Principle: "no two electrons in an atom can have the same set of quantum numbers",or, only two electrons (of opposite spin) per orbital.

ΓΕΝΙΚΑ

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The magnetic periodic table

YELLOW: ferromagnetic at room temperatureGREEN: widely encountered in magnetic compoundsPINK: of some importance in magnetismBLUE: of little importance in magnetismGRAY: of little or no importance in magnetismRED: magnetically inert

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What determines the key properties of a magnetic material?

(i) Magnetic moment per atom

(ii) Magnetization*

(iii) Curie temperature

(iv) Magnetic anisotropy**


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(1)

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D-SCHOOL-05 287Magnetic Domains in Garnet

Magnetic Domains in an Amorphous Thin Film

MAΓΝΗΤΙΚΕΣ ΠΕΡΙΟΧΕΣ


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Domain Wall Motion/Magnetization Rotation

Ordinary Ferromagnetic Materials Consisting of Magnetic Domains

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Hysteresis LoopsTypical hysteresis loops [M(H) and B(H)] for a ferromagnetic material.

(Ms)

(Mr)

(Hc)

Area under loop represents the hysteresis losses.B=H+M

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Soft and Hard Materials

M

H

Hard Materials: Sm-Co, NdFeB, CoPt, FePt, etc.

High anisotropy, High Hc

Used where a high remanence is required such as permanent magnets

Soft Materials: Co, Ni, Fe, NiFe, etc.

Low Anisotropy, low Hc

Used where a high magnetic induction and low losses are required such as transformers.

H

M

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Permanent MagnetsHard magnets, also referred to as permanent magnets, are magnetic materials that retain their magnetism after being magnetized (retain alignment without the presence of external field).

Energy has been stored in the magnets!The strongest hard magnets today are Nd-Fe-B and Sm-Co. The transition metals (Fe, Co) provide the high magnetization and the rare-earths (Nd, Sm) the high anisotropy.Maximum Energy product (BH)m is a parameter that characterizes the strength of a permanent magnet. (BH)m= (Mr/2)2 if Hc=Mr/2

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Development of (BH)max

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Nanocomposite Magnets: Next Generation Magnets

Consist of a fine mixture of soft and hard phases with enhanced remanence and energy products in the nanocomposites

bulk Multilayers

M

HH

Hard Phase High Hc

Fine mixture

M

Soft Phase High Ms Hard + Soft

M

H

Coarse

mixture

For optimum exchange coupling, Ds=2 δwh (10 nm for Nd-Fe-B)

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MAGNETIC RECORDING

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Basic Principles of Magnetic Recording

Longitudinal Recording

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MAGNETIC RECORDING

Writing data on a storage medium Reading data from a storage mediumby GMR head

RECO

RDIN

G

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GMR- RECORDING HEADS

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F

S2AF

S1

P

θ = 90° θ = 90°

θ = 180°

θ = 0°

Vsig = - JW ½ ∆ρ cosθ

θ = 90°

SPIN VALVE ANIMATIONSPIN VALVE ANIMATION

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MAGNETIC RECORDING

Computational Micromagnetics Use uniform rectangular discretizations for both media and reader stack. Magnetization M is uniform in each cell.

Magnetization damping follows Landau-Lifshitz-Gilbert Equation

MHeff)(

Mdtd

effs

eff HMMHMM××

λ−×γ=

γ = the gyromagnetic ratio of the free electron spin

λ = damping constant

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MAGNETIC RECORDING

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FUNDAMENTALS OF SPIN

1 In addition to their mass and electric charge, electrons have an intrinsic quantity of angularmomentum called spin, almost as if they were tinyspinning balls.

2 Associated with the spin is a magnetic field likethat of a tiny bar magnet lined up with the spin axis.

3 Scientists represent the spin with a vector. For a sphere spinning "west to east" the vector points"north" or "up." It points "down" for the oppositespin.

4 In a magnetic field, electrons with "spin up" and "spin down" have different energies.

5 In an ordinary electric circuit the spins areoriented at random and have no effect on currentflow.

6 Spintronic devices create spin-polarized currentsand use the spin to control current flow

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SPINTRONICS

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SPINTRONICS

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SPINTRONICS

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MEMORIES and NEW MAGNETIC MEMORIES (MRAMS)

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MEMORIES and NEW MAGNETIC MEMORIES (MRAMS)

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“ΜΑΓΝΗΤΙΚΑ ΥΛΙΚΑ ΓΙΑ ΒΙΟ-ΙΑΤΡΙΚΕΣΕΦΑΡΜΟΓΕΣ

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Magnetic Separation-Biosampling

GMR- Sensor

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Bio-Magnetic GMR Sensors

Schematic of the GMR sensor elements, showing the binding of a magnetic nanoparticle to one or the sensor elements.

Advantage over other sensing methods(Flurescent, Radioactive, etc.):

•Take advantage of GMR’ssensitivity, low cost, and high density•Constant signal•Little background•Insensitive to ambient light•More compact than optical methods•Can be manipulated externally

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FM particles possess hysteretic properties when exposed to a time varyingmagnetic field, which gives rise to magnetically induced heating. The amount ofheat generated per unit volume is given by the frequency multiplied by the areaof the hysteresis loop:

BIOMEDICAL APPLICATIONS-HYPERTHERMIA

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Advantages of nanoparticles for MFH

High Specific Adsorption Rate compared to microparticles

Cell MFH

Size Targeting of Different Organs

Different Modification of Nanoparticles for the targeting of different cellsEtc.

0 20 40 60 80 100 12020

30

40

50

60

Time (seconds)

Tem

pera

ture

(°C

)

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MRI-Enchancement

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MRI WithΜαγνητικάNanoparticlesHighly Sensitive inDetecting ProstateCancer MetastasesBy Anthony J. Brown, MD

NEW YORK Jun 18, 2003 (Reuters Health) - High-resolution MRI with magnetic nanoparticles ishighly sensitive in detecting clinically occult lymph-node metastases in prostate cancer, according toa new report. In fact, routine use of this modalitypreoperatively could obviate many unneededsurgeries.

MRI with nanoparticles correctly identified all of thepatients with nodal disease. In addition, on node-by-node analysis, the sensitivity of this modality, at90.5%, was significantly higher than that ofconventional MRI, at 35.4% (p < 0.001).

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“PM APPLICATIONS AT HIGH TEMPERATURES”

• Selected current classes of materials.- MAGNETIC MATERIALS

BULK MAGNETS-APPLICATIONS

Fig. Xenon gas is delivered to the thruster, ionized, Accelerated and neutralized.

Ion Beam Thruster

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Silicon waffer

membrane

coilsmagnets

19 coils Ø 6 mm(hexagonal array)

(=> up to several100 to 1000s pixels)

Si 2"

Deformable mirror for adaptive optics(astronomy, ophtalmology)

Array of planarmicro-coils

Magnets

Silicon ring

Flexible membrane

Reflective layer

± 5 µm

z

r

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A guide to Magnetism throughout the ages

Τhe sevem moments of magnetism

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ΕΥΧΑΡΙΣΤΙΕΣ

Dr. D. Petridis

Dr. A. Simopoulos

Dr. P. Panagiotopoulos- U of Ioannina

Dr. V. Karanasos

Dr. C. Christides- U of Patras

Dr. G. Hadjipanayis- U of Delaware

Dr. L. Castaldi

Dr. A. Tarvlos

Dr. C. Giannakopoulos

Dr. E. Devlin

Dr. V. Tzitzios

Dr. A. Speliotis

Mr. E. Manios

Mr. V. Alexandrakis

Also

Projects HIDEMAR

DYNAMICS

DYNASPIN

M2EMS

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