![Evolution of two-dimensional antiferromagnetism with ... -- multiferroic... · 2CoGe 2O 7 were grown by floating-zone technique and characterized in previous stud-ies [9,11,13,18].](https://static.fdocuments.us/doc/165x107/5c68e5da09d3f2e4258c11ee/evolution-of-two-dimensional-antiferromagnetism-with-multiferroic.jpg)
Antiferromagnetism
6
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Antiferromagnetism 1/6 Antiferromagnetism From Wikipedia, the free encyclopedia Jump to: navigation , search Antiferromagnetic ordering In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules , usually related to the spins of electrons , align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism , a manifestation of ordered magnetism . Generally, antiferromagnetic order may exist at sufficiently low temperatures, vanishing at and above a certain temperature, the Néel temperature (named after Louis Néel , who had first identified this type of magnetic ordering). [ 1 ] Above the Néel temperature, the material is typically paramagnetic . Contents [hide ] 1 Measurement 2 Antiferromagnetic materials 3 Geometric frustration 4 Other properties 5 See also 6 References 7 External links Measurement[edit ] When no external field is applied, the antiferromagnetic structure corresponds to a vanishing total magnetization. In an external magnetic field, a kind of ferrimagnetic behavior may be displayed in the antiferromagnetic phase, with the absolute value of one of the sublattice magnetizations differing from that of the other sublattice, resulting in a nonzero net magnetization. Although the net magnetization should be zero at a temperature of absolute zero , the effect of spin canting often causes a small net magnetization to develop, as seen for example in hematite . The magnetic susceptibility of an antiferromagnetic material typically shows a maximum at the Néel temperature. In contrast, at the transition between the ferromagnetic to the paramagnetic phases the susceptibility will diverge. In the antiferromagnetic case, a divergence is observed in the staggered susceptibility. Various microscopic (exchange) interactions between the magnetic moments or spins may lead to antiferromagnetic structures. In the simplest case, one may consider an Ising model on an bipartite
-
Upload
deep-joshi -
Category
Documents
-
view
7 -
download
0
description
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usuallyrelated to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices)pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation ofordered magnetism. Generally, antiferromagnetic order may exist at sufficiently low temperatures,vanishing at and above a certain temperature, the Néel temperature (named after Louis Néel, who hadfirst identified this type of magnetic ordering)
Transcript of Antiferromagnetism
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 1/6
AntiferromagnetismFrom Wikipedia, the free encyclopediaJump to: navigation, search
Antiferromagnetic ordering
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usuallyrelated to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices)pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation ofordered magnetism. Generally, antiferromagnetic order may exist at sufficiently low temperatures,vanishing at and above a certain temperature, the Néel temperature (named after Louis Néel, who hadfirst identified this type of magnetic ordering).[1] Above the Néel temperature, the material is typicallyparamagnetic.
Contents
[hide]
1 Measurement2 Antiferromagnetic materials3 Geometric frustration4 Other properties5 See also6 References7 External links
Measurement[edit]
When no external field is applied, the antiferromagnetic structure corresponds to a vanishing totalmagnetization. In an external magnetic field, a kind of ferrimagnetic behavior may be displayed in theantiferromagnetic phase, with the absolute value of one of the sublattice magnetizations differing fromthat of the other sublattice, resulting in a nonzero net magnetization. Although the net magnetizationshould be zero at a temperature of absolute zero, the effect of spin canting often causes a small netmagnetization to develop, as seen for example in hematite.
The magnetic susceptibility of an antiferromagnetic material typically shows a maximum at the Néeltemperature. In contrast, at the transition between the ferromagnetic to the paramagnetic phases thesusceptibility will diverge. In the antiferromagnetic case, a divergence is observed in the staggeredsusceptibility.
Various microscopic (exchange) interactions between the magnetic moments or spins may lead toantiferromagnetic structures. In the simplest case, one may consider an Ising model on an bipartite
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 2/6
lattice, e.g. the simple cubic lattice, with couplings between spins at nearest neighbor sites. Depending onthe sign of that interaction, ferromagnetic or antiferromagnetic order will result. Geometrical frustrationor competing ferro and antiferromagnetic interactions may lead to different and, perhaps, morecomplicated magnetic structures.
Antiferromagnetic materials[edit]
Antiferromagnetic materials occur commonly among transition metal compounds, especially oxides.Examples include hematite, metals such as chromium, alloys such as iron manganese (FeMn), and oxidessuch as nickel oxide (NiO). There are also numerous examples among high nuclearity metal clusters.Organic molecules can also exhibit antiferromagnetic coupling under rare circumstances, as seen inradicals such as 5dehydromxylylene.
Antiferromagnets can couple to ferromagnets, for instance, through a mechanism known as exchangebias, in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligningmagnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of theantiferromagnet. This provides the ability to "pin" the orientation of a ferromagnetic film, which providesone of the main uses in socalled spin valves, which are the basis of magnetic sensors including modernhard drive read heads. The temperature at or above which an antiferromagnetic layer loses its ability to"pin" the magnetization direction of an adjacent ferromagnetic layer is called the blocking temperature ofthat layer and is usually lower than the Néel temperature.
Geometric frustration[edit]
Main article: Geometrical frustration
Unlike ferromagnetism, antiferromagnetic interactions can lead to multiple optimal states (ground states—states of minimal energy). In one dimension, the antiferromagnetic ground state is an alternatingseries of spins: up, down, up, down, etc. Yet in two dimensions, multiple ground states can occur.
Consider an equilateral triangle with three spins, one on each vertex. If each spin can take on only twovalues (up or down), there are 23 = 8 possible states of the system, six of which are ground states. Thetwo situations which are not ground states are when all three spins are up or are all down. In any of theother six states, there will be two favorable interactions and one unfavorable one. This illustratesfrustration: the inability of the system to find a single ground state. This type of magnetic behavior hasbeen found in minerals that have a crystal stacking structure such as a Kagome lattice or hexagonallattice.
Other properties[edit]Synthetic antiferromagnets (often abbreviated by SAF) are artificial antiferromagnets consisting of twoor more thin ferromagnetic layers separated by a nonmagnetic layer. Due to dipole coupling of theferromagnetic layers which results in antiparallel alignment of the magnetization of the ferromagnets.
Antiferromagnetism plays a crucial role in giant magnetoresistance, as had been discovered in 1988 bythe Nobel prize winners Albert Fert and Peter Grünberg (awarded in 2007) using syntheticantiferromagnets.
There are also examples of disordered materials (such as iron phosphate glasses) that become
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 3/6
antiferromagnetic below their Néel temperature. These disordered networks 'frustrate' the antiparallelismof adjacent spins; i.e. it is not possible to construct a network where each spin is surrounded by oppositeneighbour spins. It can only be determined that the average correlation of neighbour spins isantiferromagnetic. This type of magnetism is sometimes called speromagnetism.
See also[edit]
Exchange biasGiant magnetoresistanceGeometrically frustrated magnetIsing modelANNNI modelMottnessQuantum spin liquid
References[edit]1. L. Néel, Propriétées magnétiques des ferrites; Férrimagnétisme et antiferromagnétisme, Annales de Physique
(Paris) 3, 137–198 (1948).
External links[edit]Magnetism: Models and Mechanisms in E. Pavarini, E. Koch, and U. Schollwöck: EmergentPhenomena in Correlated Matter, Jülich 2013, ISBN 9783893368846
Retrieved from "https://en.wikipedia.org/w/index.php?title=Antiferromagnetism&oldid=671466724"Categories:
Quantum phasesMagnetic orderingQuantum Lattice models
Hidden categories:
Articles needing additional references from May 2014All articles needing additional references
Navigation menu
Personal tools
Create accountNot logged inTalkContributionsLog in
Namespaces
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 4/6
ArticleTalk
Variants
Views
ReadEditView history
More
Search
SearchGo
Navigation
Main pageContentsFeatured contentCurrent eventsRandom articleDonate to WikipediaWikipedia store
Interaction
HelpAbout WikipediaCommunity portalRecent changesContact page
Tools
What links hereRelated changesUpload fileSpecial pagesPermanent linkPage informationWikidata itemCite this page
Print/export
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 5/6
Create a bookDownload as PDFPrintable version
Languages
العربيةCatalàČeštinaDeutschEestiEspañolEsperantoFrançais한국어ՀայերենItalianoעבריתҚазақшаКыргызчаNederlands日本語Norsk nynorskOʻzbekcha/ўзбекчаPolskiPortuguêsRomânăРусскийSlovenčinaSuomiSvenskaTürkçeУкраїнськаTiếng Việt中文
Edit links
This page was last modified on 14 July 2015, at 22:09.Text is available under the Creative Commons AttributionShareAlike License; additional termsmay apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is aregistered trademark of the Wikimedia Foundation, Inc., a nonprofit organization.
Privacy policyAbout WikipediaDisclaimersContact WikipediaDevelopersMobile view
9/29/2015 Antiferromagnetism Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Antiferromagnetism 6/6
