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Topic: Antiferromagnetism


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  Antiferromagnetic images seen in solids
In contrast to familiar magnets such as iron, antiferromagnets are difficult to identify.
Antiferromagnets are “anti” because the fields for neighboring atoms align in opposite directions.
The researchers made X-rays of chromium's antiferromagnetic domains—regions in which the atomic magnetism lies along a particular direction.
www.anl.gov /Media_Center/Frontiers/2003/c2facil.html   (386 words)

  
 Reference.com/Encyclopedia/Antiferromagnetism
Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Néel temperature.
The antiferromagnetic behaviour at low temperature usually results in diamagnetic properties, but can sometimes display ferrimagnetic behaviour, which in many physically observable properties is more similar to ferromagnetic interactions.
Antiferromagnets can also couple to ferromagnetic materials through a mechanism known as exchange anisotropy, in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligning magnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of the antiferromagnet.
www.reference.com /browse/wiki/Antiferromagnet   (374 words)

  
 Synchrotron radiation reveals secrets of antiferromagnetism
There are many different materials with ferromagnetic and antiferromagnetic properties, "but read heads are constructed from these on a trial-and-error basis," says Joachim Stöhr of the IBM Almaden Research Center in San Jose.
To image antiferromagnetic domains, in which spins are aligned opposite to each other, linear polarization is needed.
Lanthanum iron oxide is an antiferromagnetic material whose domain structure is large enough to be resolved by the PEEM2, but it is not the material used in technological devices.
www.eurekalert.org /pub_releases/2000-02/LBNL-Srrs-0902100.php   (1022 words)

  
  EPG471: Photoelectron Spectroscopy Studies of Cr(001) Near-Surface Antiferromagnetism and Surface Ferromagnetism   (Site not responding. Last check: )
Photoelectron Spectroscopy Studies of Cr(001) Near-Surface Antiferromagnetism and Surface Ferromagnetism
The periodicity of these band dispersions indicates that the valence electrons experience and self-consistently establish antiferromagnetism in the near-surface layers of Cr(001).
Almost all of the spectral observations are consistent with a surface-sentitive enhancement of the atomic 3d spin at the Cr(001) surface.
www.physics.nist.gov /Divisions/Div841/Gp3/Pubs/abstract/epg471.html   (204 words)

  
  Antiferromagnetism - Wikipedia, the free encyclopedia
Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Néel temperature.
The antiferromagnetic behaviour at low temperature usually results in diamagnetic properties, but can sometimes display ferrimagnetic behaviour, which in many physically observable properties is more similar to ferromagnetic interactions.
Antiferromagnets can also couple to ferromagnetic materials through a mechanism known as exchange anisotropy, in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligning magnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of the antiferromagnet.
www.sciencedaily.com /encyclopedia/antiferromagnetism   (391 words)

  
 NationMaster - Encyclopedia: Antiferromagnetism
Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Neel temperature.
A ferrimagnetic interaction is a specific type of antiferromagnetic interaction in which the net spin of the system is not equal to zero due to the spin in each direction not being equal, and therefore not cancelling.
Lanthanum iron oxide is an antiferromagnetic material whose domain structure is large enough to be resolved by the PEEM2, but it is not the material used in technological devices.
www.nationmaster.com /encyclopedia/Antiferromagnetism   (1006 words)

  
 [No title]
For paramagnetism, antiferromagnetism, and diamagnetism, the important quantities are the magnetization and the magnetic susceptibility; the susceptibility, represented by the Greek lower case letter chi, is the ratio of magnetization to applied field.
Antiferromagnetism Antiferromagnetism is characterized by an antiparallel pattern of magnetic moments below a critical temperature called the Neel temperature, named for French physicist Louis Neel.
Antiferromagnetism was first verified in 1939 in manganous oxide.
www.angelfire.com /co2/eradani7/magnet.html   (2827 words)

  
 ScienceWeek
Antiferromagnetism has been theoretically predicted(3,4) to be the competing ground state.
A competing ground state is revealed when superconductivity is destroyed by the application of a magnetic field, and antiferromagnetism has been observed in hole-doped materials under the influence of modest fields(5).
This and previous experiments on the hole-doped materials therefore establishes antiferromagnetic order as a competing ground state in the high-Tc copper oxide materials, irrespective of electron or hole doping.
scienceweek.com /2003/sw030808-3.htm   (702 words)

  
 Researchers Examining Phenomenon of Antiferromagnetism Underlying Computer Read Heads
Not as catchy as The Magic Flute, but a lot more practical: antiferromagnetism is a phenomenon vital to the layered structures of today's advanced computer hard-disk read heads and to the memory devices of the future.
While spins in the magnetic domains of antiferromagnetic materials are also parallel, they alternately point in opposite directions, so on average the material is insensitive to applied magnetic fields.
Because exchange-bias devices such as read heads depend upon an overall preferred magnetic orientation in a ferromagnetic layer coupled to an antiferromagnet layer, a "bias" is set during the manufacturing process.
www.lbl.gov /LBL-Science-Articles/Archive/antiferromagnetism-surprise.html   (1018 words)

  
 Physics Today October 2001
Then, assuming that short-range interactions could be antiparallel, Néel developed the concept of antiferromagnetism, in which two interpenetrating atomic lattices are treated in a molecular field approximation.
To describe antiferromagnetism, Lev Landau and Cornelis Gorter suggested quantum fluctuations to mix Néel's solution with that obtained by reversal of moments.
Néel's difficulties with antiferromagnetism and inconclusive discussions in the Strasbourg international meeting of 1939 fostered his skepticism about the usefulness of quantum mechanics; this was one of the few limitations of this superior mind.
www.physicstoday.org /vol-54/iss-10/p88.html   (926 words)

  
 Physics Today June 2002
Shull's obituary, in which he is consistently called "Cliff," says that Shull confirmed antiferromagnetism in manganese oxide, presumably after 1938 (after the "war ended") and confirmed the Néel model for ferrimagnetism for magnetite, probably around 1950, as I interpret it.
Maybe people used to call Cliff "Harry." Maybe the development of the theory of "antiferromagnetism" for manganese oxide is so related to the theory of "ferrimagnetism" for magnetite that distinctions about what "Harry" confirmed, and when and how, are not so important.
originated the name antiferromagnetism in developing a theory of systems in which the magnetic interaction between atoms on crystallographically equivalent sites favored opposite orientation of the magnetic moments on nearest neighbors.
www.physicstoday.org /pt/vol-55/iss-6/p10c.html   (535 words)

  
 Introduction to Magnetochemistry
Antiferromagnetic - When unpaired electrons are held in an alignment with an equal number of spins in each direction, the substance is strongly repelled by a magnet.
The advantage of using effective magnetic moments for describing paramagnetic behavior is that it is a measure of the materials magnetic behavior which is not dependent upon either the temperature or the magnitude of the external field.
Antiferromagnetic compounds show an increase in magnetic susceptibility until their critical temperature, called the Neel temperature, is reached.
server.ccl.net /cca/documents/dyoung/topics-orig/magnet.html   (2840 words)

  
 Model study of antiferromagnetism in high-Tc superconducting oxides.
Model study of antiferromagnetism in high-Tc superconducting oxides.
Oles A.M., Zaanen J. The antiferromagnetic ground state in high-Tc superconducting oxides (HTSO) is studied with a two-band model Hamiltonian by using a Hartree-Fock approximation and the Gutzwiller ansatz.
It is found that the magnetic moments of Cu atoms and the antiferromagnetic gap agree well with the available experimental data for HTSO.
www.fkf.mpg.de /andersen/docs/pub/abstract/and1988-35.html   (77 words)

  
 Classification  of Magnetic Materials
Finally, magnetic materials can also be classified as ferrimagnetic although this is not observed in any pure element but can only be found in compounds, such as the mixed oxides, known as ferrites, from which ferrimagnetism derives its name.
In the periodic table the only element exhibiting antiferromagnetism at room temperature is chromium.
Antiferromagnetic materials are very similar to ferromagnetic materials but the exchange interaction between neighbouring atoms leads to the anti-parallel alignment of the atomic magnetic moments.
www.aacg.bham.ac.uk /magnetic_materials/type.htm   (1102 words)

  
 Properties of Magnetic Materials
There are three general types of magnetic behaviors: paramagnetism, in which the unpaired electrons are randomly arranged, ferromagnetism, in which the unpaired electrons are all aligned, and antiferromagnetism, in which the unpaired electrons line up opposite of one another.
A compound is defined as being ferrimagnetic if the electron spins are orientated antiparrallel to one another but, due to an inequality in the number of spins in each orientation, there exists an overall magnetic moment.
Antiferromagnetic materials can be distinguished from paramagnetic substances in that the value of χ increases with temperature, whereas χ shows no change or decreases in value as temperature rises for paramagnetic compounds.
www.sigmaaldrich.com /Area_of_Interest/Chemistry/Materials_Science/Energy_Source_Materials/Magnetic_Materials/Tutorial/Properties.html   (521 words)

  
 feat11
For a given frequency, the excitations are strongest near the wavevector characterizing the antiferromagnetism Q=(1/2,1/2) - in fact, spin waves lie on a small circle centred on (1/2,1/2).
Doping causes the antiferromagnetism to be destroyed and superconductivity to appear.
In spite of the disappearance of the antiferromagnetism, strong overdamped magnetic excitations still persist for superconducting compositions.
www.isis.rl.ac.uk /isis98/feat11.htm   (871 words)

  
 JYI: Magnetism in Superconducting Tl2223   (Site not responding. Last check: )
Antiferromagnetism is a type of magnetism in solids whereby adjacent ions that behave as tiny magnets spontaneously align themselves at relatively low temperatures into opposite directions throughout the material, resulting in almost no net external magnetism.
In antiferromagnetic materials, which include certain metals and alloys in addition to some ionic solids, the magnetism from magnetic atoms or ions oriented in one direction is canceled out by the set of magnetic atoms or ions that are aligned in the reverse direction.
Mitrovic, VF et al (2003) Antiferromagnetism in the vortex cores of YBa2Cu3O7.
www.jyi.org /volumes/volume10/issue6/articles/prudchenko.html   (1757 words)

  
 Physics Today October 2001
Then, assuming that short-range interactions could be antiparallel, Néel developed the concept of antiferromagnetism, in which two interpenetrating atomic lattices are treated in a molecular field approximation.
To describe antiferromagnetism, Lev Landau and Cornelis Gorter suggested quantum fluctuations to mix Néel's solution with that obtained by reversal of moments.
Néel's difficulties with antiferromagnetism and inconclusive discussions in the Strasbourg international meeting of 1939 fostered his skepticism about the usefulness of quantum mechanics; this was one of the few limitations of this superior mind.
www.aip.org /pt/vol-54/iss-10/p88.html   (926 words)

  
   Theoretical Physics Research Group
The worst structures are the geometrically frustrated lattices, for which there are a variety of possible styles of antiferromagnetism.
The initial task is to try to classify the possible types of antiferromagnetism and assess on symmetry grounds which are the most likely to be observed in nature.
The open-ended part of the project is to investigate which states are preferred by a variety of physical phenomena; Longer-range interactions, temperature, structural distortion, disorder, alloying and quantum mechanics for example, and to try to understand the likely phase transitions to be observed in this style of system.
www.th.ph.bham.ac.uk /ug_courses/projects/hex.htm   (194 words)

  
 Balents Group Research
The most interesting is the transition from a Neél antiferromagnet to a valence bond solid state on a square lattice.
This provides an answer to the old question of how antiferromagnetism is destroyed by frustration in a spin-1/2 magnet (though we described the situation for general spin, and with magnetic anisotropy).
The mechanism for this transition is novel: the topological defects of either phase (skyrmions/vortices in the antiferromagnet and domain walls and their intersections in the valence bond solid) can be shown to carry unusual quantum numbers, such that when they proliferate as their associated order is destroyed, they induce the order of the neighboring phase.
www.physics.ucsb.edu /~balents/research.htm   (5589 words)

  
 Antiferromagnetism, Ferromagnetism, and Phase Separation in the GMR System Sr2-xLa1+xMn2O7
The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters.
The majority phase (81%) adopts a collinear antiferromagnetic structure below ~210 K whereas the minority phase is ferromagnetically ordered below ~125 K. The ordered magnetic moments lie in the xy plane in both phases.
The behavior observed is discussed in terms of the interplay between structural and electronic factors.
pubs.acs.org /cgi-bin/jtext?cmatex/9/i04/abs/cm960632d   (197 words)

  
 Indian physicist makes breakthrough in metallic magnetism
Theoretical understanding of why "frustrated" materials like the sodium cobalt oxide are antiferromagnetic has remained unsolved for the past 40 years.
In antiferromagnetism, the spins align in a regular pattern with neighbouring spins pointing in opposite directions, or anti-parallel.
The kinetic antiferromagnetism in a triangular lattice described by Shastry and Haerter results from the movement of electrons when there is a single "electron hole," or unoccupied site for an electron, in the lattice.
www.expressindia.com /fullstory.php?newsid=53432   (671 words)

  
 Synchrotron Radiation Reveals Secrets Of Antiferromagnetism
PEEM2 was built under a joint Corporate Research and Development Agreement between the IBM Corporation and Berkeley Lab, in collaboration with Arizona State University.
There are many different materials with ferromagnetic and antiferromagnetic properties, "but read heads are constructed from these on a trial-and-error basis," says Joachim Stöhr of the IBM Almaden Research Center in San Jose.
The Néel temperature (like the Curie temperature of other magnetic materials) is the temperature at which antiferromagnetic materials lose magnetism.
www.lbl.gov /Science-Articles/Archive/antiferromagnetism.html   (1052 words)

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