Levitating pyrolytic carbon

Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is the result of changes in the orbital motion of electrons. Applying a magnetic field creates a magnetic force on a moving electron in the form of F = Qv × B. This force changes the centripetal force on the electron, causing it to either speed up or slow down in its orbital motion. This changed electron speed modifies the magnetic moment of the orbital in a direction opposing the external field. Image File history File links Download high resolution version (550x700, 153 KB)A small (~6mm) piece of pyrolytic graphite levitating over a permanent neodymium magnet array (5mm cubes on a piece of steel). ... Image File history File links Download high resolution version (550x700, 153 KB)A small (~6mm) piece of pyrolytic graphite levitating over a permanent neodymium magnet array (5mm cubes on a piece of steel). ... Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... Magnetic lines of force of a bar magnet shown by iron filings on paper In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials. ... For other senses of this term, see magnetic field (disambiguation). ... The centripetal force is the external force required to make the body move in a circular path with uniform speed and directed towards the center. ... A bar magnet. ...

Consider two electron orbitals; one rotating clockwise and the other counterclockwise. An external magnetic field into the page will make the centripetal force on an electron rotating clockwise increase, which increases its moment out of the page. That field would make the centripetal force on an electron rotating counterclockwise decrease, decreasing its moment into the page. Both changes oppose the external magnetic field into the page. However, the induced magnetic moment is very small in most everyday materials.

All materials show a diamagnetic response in an applied magnetic field; however for materials which show some other form of magnetism (such as ferromagnetism or paramagnetism), the diamagnetism is completely overpowered. Substances which only, or mostly, display diamagnetic behaviour are termed diamagnetic materials, or diamagnets. Materials that are said to be diamagnetic are those which are usually considered by non-physicists as "non magnetic", and include water, DNA, most organic compounds such as oil and plastic, and many metals such as mercury, gold and bismuth. Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ... Simple Illustration of a paramagnetic probe made up from miniature magnets. ... Impact of a drop of water Water is a chemical substance that is essential to all known forms of life. ... The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Atomic mass 200. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ...

Diamagnetic materials have a relative magnetic permeability that is less than 1, thus a magnetic susceptibility which is less than 0, and are therefore repelled by magnetic fields. However, since diamagnetism is such a weak property its effects are not observable in every-day life. For example, the magnetic susceptibility of diamagnets such as water is = −9.05×10⁻⁶. The most strongly diamagnetic material is bismuth, = −166×10⁻⁶, although pyrolytic graphite may have a susceptibility of = −400×10⁻⁶ in one plane. Nevertheless these values are orders of magnitudes smaller than the magnetism exhibited by paramagnets and ferromagnets. Superconductors may be considered to be perfect diamagnets ( = −1), since they expel all field from their interior due to the Meissner effect. This article is in need of attention. ... In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ... In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ... General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ... Meissner effect Diagram of the Meissner effect. ...

History

In 1778 S. J. Brugmans was the first person to observe that bismuth and antimony were repelled by magnetic fields. However, the term "diamagnetism" was coined by Michael Faraday in September 1845, when he realized that all materials in nature possessed some form of diamagnetic response to an applied magnetic field. General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ... General Name, Symbol, Number antimony, Sb, 51 Chemical series metalloids Group, Period, Block 15, 5, p Appearance silvery lustrous grey Atomic mass 121. ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed significantly to the fields of electromagnetism and electrochemistry. ...

Diamagnetic levitation

A live frog levitates inside a 32 mm diameter vertical bore of a Bitter solenoid in a magnetic field of about 16 teslas at the Nijmegen High Field Magnet Laboratory. Movie

A particularly fascinating phenomenon involving diamagnets is that they may be levitated in stable equilibrium in a magnetic field, with no power consumption. Earnshaw's theorem seems to preclude the possibility of static magnetic levitation. However, Earnshaw's theory only applies to objects with permanent moments m, such as ferromagnets, whose magnetic energy is given by m·B. Ferromagnets are attracted to field maxima, which do not exist in free space. Diamagnetism is an induced form of magnetism, thus the magnetic moment is proportional to the applied field B. This means that the magnetic energy of diamagnets is proportional to B², the intensity of the magnetic field. Diamagnets are also attracted to field minima, and there can be a minimum in B² in free space (in fact ). Image File history File links Frog_diamagnetic_levitation. ... Image File history File links Frog_diamagnetic_levitation. ... A Bitter electromagnet or Bitter solenoid is a type of electromagnet made of metal plates and insulating spacers stacked in a helix configuration, rather than coils of wire. ... SI unit. ... Earnshaws theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. ...

A thin slice of pyrolytic graphite, which is an unusually strong diamagnetic material, can be stably floated in a magnetic field, such as that from rare earth permanent magnets. This can be done with all components at room temperature, making a visually effective demonstration of diamagnetism. Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... Ferrofluid on glass, with a rare-earth magnet underneath. ...

The Radboud University Nijmegen has conducted experiments where they have successfully levitated water and a live frog, amongst other things.^[1] The Radboud University Nijmegen, formerly called Catholic University of Nijmegen is the university of the Dutch city of Nijmegen. ...

Magnetic lines of force of a bar magnet shown by iron filings on paper In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials. ... Superdiamagnetism (or perfect diamagnetism) is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of magnetic susceptibility and the exclusion of the interior magnetic field. ... Simple Illustration of a paramagnetic probe made up from miniature magnets. ... Superparamagnetism is a phenomenon by which magnetic materials may exhibit a behavior similar to paramagnetism even when at temperatures below the Curie or the Néel temperature. ... Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ... In materials that exhibit antiferromagnetism, the spins of magnetic electrons align in a regular pattern with neighboring spins pointing in opposite directions. ... In physics, a ferrimagnetic material is one in which the magnetic moment of the atoms on different sublattices oppose as in antiferromagnetism but the opposing moments are unequal and a spontaneous magnetization remains. ... Metamagnetism is a physical state of matter characterized by a superlinear increase of magnetization over a narrow range of applied magnetic field. ... A spin glass is a disordered material exhibiting high magnetic frustration. ...

References

1. ^ http://www.hfml.sci.kun.nl/froglev.html

External links

• Videos of frogs and other diamagnets levitated in a strong magnetic field
• Video of levitating pyrolytic graphite
• Video of a piece of neodymium magnet levitating between blocks of bismuth.
  • Website about this device, with images (in finnish).