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Magnetism - a mysterious force of nature and some of its consequences. Peter Day Royal Institution and UCL, London. Magnets in Nature A magnetic rock – lodestone (Fe 3 O 4 ). The name ‘magnet’ comes from Magnesia in Greece, where lodestone is found. Picture from Wikipedia.

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Magnetism a mysterious force of nature and some of its consequences

Magnetism- a mysterious force of natureand some of its consequences

Peter Day

Royal Institution and UCL, London


Magnets in nature a magnetic rock lodestone fe 3 o 4
Magnets in NatureA magnetic rock – lodestone (Fe3O4)


The name magnet comes from magnesia in greece where lodestone is found
The name ‘magnet’ comes from Magnesia in Greece, where lodestone is found

Picture from Wikipedia


Magnets in nature magnetite particles in bacteria
Magnets in Nature lodestone is foundMagnetite particles in bacteria


In 1851 michael faraday gave the christmas lectures for young people at the royal institution
In 1851 Michael Faraday gave the Christmas Lectures for young people at the Royal Institution


He wanted to illustrate chemistry and physics with an everyday 1851 object
He wanted to illustrate chemistry and physics with an everyday (1851) object

What did he choose?

A candle!


The christmas lectures today
The Christmas Lectures today everyday (1851) object

What everyday object would Faraday use now?


An ipod
An iPod?? everyday (1851) object

And how does it work?MAGNETISM!


The first serious experimental everyday (1851) object

work on magnetism:

William Gilbert, 1628


Beating wrought iron induces magnetism everyday (1851) objectMagnetic domains align in the earth’s field when the material is malleable

From Gilbert, de Magnete


Some other insights from gilbert
Some other insights from Gilbert everyday (1851) object

Lodestone loses its magnetism on heating:“fire destroys the magnetic virtues in a stone, not because it takes away any parts specially attractive, but because the consuming force of the flame mars by the demolition of the material the form of the whole”

Only a few solids are magnetic“why has nature been so stingy as to provide only a small number…”

A piece of wrought iron has a North and South pole and, if cut in half, each of the fragments has, too


Atomic magnets how they line up
Atomic magnets- how they line up everyday (1851) object

Ferromagnet

Antiferromagnet

Ferrimagnet

Canted antiferromagnet

Helimagnet


Further insights came from this man michael faraday
Further insights came from this man everyday (1851) objectMichael Faraday

  • Magnetism and electricity

  • electromagnetic induction

  • electric motors and generators

  • Lines of magnetic flux

  • - concept of ‘fields’ (Maxwell)

  • Paramagnetism and diamagnetism

  • - universal property of matter

  • Magnetism and light

  • - light as electromagnetic radiation

1791- 1867


Moving a magnet through a coil generates electricity
Moving a magnet through a coil generates electricity everyday (1851) object

Faraday’s sketch from his notebook


The apparatus and how it works
The apparatus and how it works everyday (1851) object

From the Faraday Museum,

Royal Institution, London

The world’s first electricity generator!


Electromagnetic rotation
Electromagnetic rotation everyday (1851) object

Experimental setup

The world’s first electric motor!

Faraday’s notebook


Lines of magnetic flux
Lines of magnetic flux everyday (1851) object

Iron filings experiment

Published sketch


Two demonstration experiments
Two demonstration experiments everyday (1851) object

Electromagnet attracts many

objects – even through glass!

Throwing iron filings at a box containing a hidden magnet


Paramagnetism and diamagnetism
Paramagnetism and diamagnetism everyday (1851) object

Search for diamagnetism:

Faraday’s ‘great electromagnet’

Magnetic flux lines in

para- & diamagnets



Faraday s magnetic laboratory
Faraday’s ‘Magnetic Laboratory’ everyday (1851) object

Watercolour by Charlotte Moore


Magnetism and light
Magnetism and light everyday (1851) object

Faraday’s notebook

Arrangements of magnet

pole-pieces and glass



What kind of materials behave as ferro or ferrimagnets
What kind of materials behave as ferro- or ferrimagnets? effect

  • A few metallic elements

    – iron, nickel

  • Intermetallic compounds

    – LaCo5

  • Ternary oxides (ferrimagnets)

    – Magnetite (Fe3O4), Garnets (Y3Fe5O12), Magnetoplumbites (PbFe12 O19)


These are all opaque metals or semiconductors effectAre there any magnets that are electrical insulators and hence transparent?

Very few!

In 1976 we made some – they were also soluble because they contain molecules


A 2 crcl 4 transparent ferromagnets
A effect2CrCl4: transparent ferromagnets

Bellitto and Day 1976


Solvent soluble ferromagnets c n h 2n 1 nh 3 2 crx 4
Solvent-soluble ferromagnets effect(CnH2n+1NH3)2CrX4

Crystal structure

Magnetisation

Bellitto and Day 1978

Hysteresis


Prussian blue first made in 1704 was first shown to be a ferromagnet in the 1970s
Prussian Blue (first made in 1704) was first shown to be a ferromagnet in the 1970s

Guedel et al, 1973; Mayoh and Day, 1975


The first purely organic ferromagnet p nitrophenyl nitronylnitroxide
The first purely organic ferromagnet ferromagnet in the 1970sp-nitrophenyl-nitronylnitroxide

Kinoshita et al 1991


Single molecule magnets
Single molecule magnets ferromagnet in the 1970s

Fe8

Mn12

Lis 1980

Sessoli & Gatteschi 1993

Wieghardt 1984

Gatteschi 1993


Mn 12 is a hard magnet
Mn ferromagnet in the 1970s12 is a ‘hard’ magnet

Remnant Magnetisation

Bistability : in zero field the magnetisation can be positive or negative depending on the sample history

Coercive Field

Sessoli & Gatteschi 1993


Mn ferromagnet in the 1970s12

The magnetisation relaxes very slowly at low temperature

Can this molecule be used to store information??

Magnetisation vs. time at low temperature

Wernsdorfer et al 2000


Another way to store information using magnetism
Another way to store information using magnetism ferromagnet in the 1970s

Grunberg 1986



And this is the basis of the ipod
And this is the basis of the resistanceiPod!

Three cheers for magnetism!


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