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Topic: Antiferromagnetic interaction

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Ferromagnetic interaction

Mean Field Theory

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	08.16.2004 - Vibrations in crystal lattice plays big role in high temperature superconductors
		The pairing is made possible by interactions between the electrons and the metal atoms vibrating in place in the crystal lattice.
		The alternating spin arrangement that characterizes spin-Peiels behavior is identical to the antiferromagnetic situation in high temperature superconductors.
		The team believes, then, that the mutual feedback of the magnetic and electron-phonon interaction is critical to the high temperature superconducting state.
	www.berkeley.edu /news/media/releases/2004/08/16_Lanzara.shtml (1184 words)

	Ferromagnetic interaction - Wikipedia, the free encyclopedia
		If the energy is expressed as the sum of all pairs, i, j, over an interaction term J(i,j), times the spin of atom i times the spin of atom j, J<0 is a ferromagnetic interaction (aligning spins leads to a lower total energy and is thus favorable energetically, although unfavorable entropically).
		J>0 is an antiferromagnetic interaction acting to anti-align neighboring spins.
		The combination of both can lead to spin glass behavior.
	en.wikipedia.org /wiki/Ferromagnetic_interaction (119 words)

	Jahrbuch-CD der MPG 2003 - Structure and magnetic interact
		The intermolecular interaction is accompanied by spin transfer from R-.
		The nature and the magnitude of the magnetic interaction in these structures are investigated using the band theory.
		At a given topology and geometry of the MMRC stacks the antiferromagnetic interaction in the parent molecular radical crystals...R-.....R-.....
	www.mpg.de /forschungsergebnisse/wissVeroeffentlichungen/archivListenJahrbuch/2002/58/publZIM85.html (191 words)

	[No title]
		The origin of the internal field Hi is the exchange interaction, which reflects the electrostatic Coulomb repulsion of electrons on neighbouring atoms and the Pauli principle, which forbids two electrons from entering the same quantum state.
		In a roughly half-filled band the exchange is antiferromagnetic, whereas in a nearly-filled or nearly empty band it tends to be ferromagnetic (Fig 6.6) Fig 6.6 Electron delocalization in d-bands which are half-full, or almost empty or almost full.
		Elements in the middle of the series Cr, V are antiferromagnetic because the 3d band is approximately half-full.
	www.maths.tcd.ie /~pwalsht/WEBpdf/3015/3015-6.doc (2918 words)

	Abstracts Franz Wegner
		Two applications in condensed matter physics are given as examples: The interaction of an n-orbital model of fermions in the limit of large n is brought to block-diagonal form, and the generation of the effective attractive two-electron interaction due to the elimination of electron-phonon interaction is given.
		Interactions small in comparison to this strong interaction introduce anisotropies into the SO(5)-space and determine whether it is favorable for the system to be superconducting or antiferromagnetic.
		Two applications in condensed matter physics are given as examples: (i) the interaction of an n-orbital model of fermions in the limit of large n is brought to block-diagonal form, and (ii) the generation of the effective attractive two-electron interaction due to the elimination of electron-phonon interaction is given.
	www.tphys.uni-heidelberg.de /~wegner/Abstracts.html (11186 words)

	T_research
		Their periodicity as a function of flux is doubled for strong enough repulsive interactions because electrons cannot hop coherently between the chains and have to travel along the full edge of the Moebius ladder, thus encircling the flux twice.
		The interplay of topology and interactions is shown to lead to interesting finite-size effects on the odd harmonics of the persistent current.
		The competition between the entropy carried by the holons and that carried by the backflow of the spinons gives rise to an unusual temperature and doping dependence of the thermopower which is qualitatively similar to that observed in the normal state of high- T c superconductors and certain quasi-one-dimensional organic conductors.
	www.physics.arizona.edu /~stafford/oned.html (782 words)

	Research Area: Magnetic semiconductors
		This suggests a competition between two interactions: a weak antiferromagnetic interaction due to superexchange, and a ferromagnetic interaction due to an indirect exchange mechanism mediated by free carriers.
		When a divalent dopant such as Mn substitutes for a Group III atom such as Ga, a hole is introduced; this is the reason GaAs becomes ferromagnetic while ZnSe does not.
		Interestingly, this coupling is antiferromagnetic for nearest-neighbor Mn atoms, but ferromagnetic for most separations greater than this.
	dave.nrl.navy.mil /ResearchAreas/MagneticSemiconductors (811 words)

	Condensed Matter Theory - Florian Meier
		Depending on the quantum dot energy level scheme, the interaction of a singly doped quantum dot with a cavity photon generates entanglement of electron spin and cavity states or allows one to implement a SWAP gate for spin and photon states.
		Molecular magnetic clusters with antiferromagnetic exchange interaction and easy axis anisotropy belong to the most promising candidate systems for the observation of coherent spin quantum tunneling on the mesoscopic scale.
		Antiferromagnetic molecular clusters are promising candidates for the observation of coherent quantum tunneling on the mesoscopic scale.
	theorie5.physik.unibas.ch /meier (2119 words)

	Correlations in Arrays of Superconducting Rings
		Two nearby but electrically isolated rings can interact magnetically; this interaction favors an antiparallel alignment of moments and is thus analogous to an antiferromagnetic spin-spin interaction.
		This "antiferromagnetic" configuration of the two spins is thus especially stable.
		We have searched for antiferromagnetic correlations between moments in the rings arrays using a variety of techniques, including SQUID susceptometry and scanning Hall probe microscopy.
	www.physics.colostate.edu /groups/fieldgroup/Rings.html (559 words)

	\bigrmbf Antiferromagnetic exchange and spin-fluctuation pairing mechanisms in cuprates (Site not responding. Last check: 2007-10-27)
		Antiferromagnetic exchange and spin-fluctuation pairing mechanisms in cuprates
		We have proved, by a direct calculation of these functions without any decoupling, that the pairing is mediated by the conventional antiferromagnetic exchange interaction J originating from the interband hopping, as in the t-J model, and is driven by the lowering of kinetic energy.
		The self-energy derived in the second order of the intraband hopping describes the spin-fluctuation d-wave pairing induced by the kinematic interaction.
	phyvax.ir.miami.edu:8001 /hts04/prog_abstracts/plakida_nikolay_1.html (230 words)

	Jahn-Teller distortion and magnetoresistance in electron doped Sr1-xCexMnO3(x = 0.1, 0.2, 0.3 and 0.4)
		The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the
		Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance appears for
		The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size may be responsible for the absence of double exchange ferromagnetism and CMR effect.
	www.edpsciences.org /articles/epjb/abs/2000/07/b9576/b9576.html (297 words)

	Antiferromagnetic Exchange Interaction among the Three Spins Placed in an Isosceles Triangular Configuration in ...
		Antiferromagnetic Exchange Interaction among the Three Spins Placed in an Isosceles Triangular Configuration in 2,4-Dimethoxy-1,3,5-benzenetriyltris(N-tert-butyl nitroxide)
		Temperature dependence of molar susceptibility for a microcrystalline sample obtained by SQUID measurements suggested that the antiferromagnetic interaction produces a doublet ground state in triradical 3.
		In triradical 3, therefore, the ground spin state would be a doublet with the stronger antiferromagnetic interaction between the spins at 1 and 3 positions and 3 and 5 positions polarizing the ferromagnetic alignment of the 1 and 5 spins, providing the first demonstration of an organic triradical showing competing interactions.
	pubs.acs.org /cgi-bin/abstract.cgi/jacsat/1996/118/i39/abs/ja961849b.html (327 words)

	6.1.1 Theories
		In order to estimate the conditions for spin Peierls transition, a quantum mechanical treatment of the spin system is necessary, because singlet-pair formations are involved in the transition mechanism.
		is the antiferromagnetic interaction between the spins on the i-th and the
		In zero-field, the ground state is either the Néel state or spin-Peierls state, depending on the magnitude of the inter-chain interaction.
	musr.physics.ubc.ca /theses/Kojima/node62.html (766 words)

	[No title]
		The elementary excitations from the magnetic ground state are spin waves (magnons) which are described by a dispersion relation E = Dswq2 in the ferromagnetic caase.
		When ferromagnetic and antiferromagnetic interactions compete, and cannot all be satisfied simultaneously, the system is said to be frustrated.
		In disordered and amorphous solids, frustrated antiferromagnetic interactions, or competing ferromagnetic and antiferromagnetic interactions may give rise to spin freezing in random directions.
	www.maths.tcd.ie /~pwalsht/WEBpdf/3015/3015-7.doc (816 words)

	Magnetic interactions and the co-operative Jahn-Teller effect in KCuF3
		For each system, the total energy difference between ferro- and antiferromagnetic states at the same geometry is ‘normalized’ to -1, and differences in the various components of the total energy between the two phases defined relative to this.
		In the antiferromagnetic states, there is a spin polarization of the fluorine ion, since the spatial orbitals are no longer constrained to be orthogonal, and thus the exchange repulsion may be reduced by shifting alpha density towards the Cu ion with beta polarization, and vice versa.
		For antiferromagnetic superexchange contacts, the lowering of kinetic energy is the dominant contribution, while in the equivalent ferromagnetic interaction in orbitally-ordered planes, the electron-nuclear repulsion predominates.
	www.tcm.phy.cam.ac.uk /~mdt26/kcuf3/kcuf3.html (5319 words)

	Research Area: Magnetic Materials
		We have recently suggested that a vibrationally induced modification of the spin-orbit interaction may be an important interaction.
		This suggests a competition between two interactions: a weak antiferromagnetic interaction due to superexchange, and a ferromagnetic interaction due to an indirect exchange mechanism mediated by free carriers.
		Interestingly, this coupling is antiferromagnetic for nearest-neighbor Mn atoms, but ferromagnetic for all separations greater than this.
	cst-www.nrl.navy.mil /ResearchAreas/MagneticMaterials (1053 words)

	ILL : ANNUAL REPORT 2001
		A linear array of such spins 1/2 coupled by antiferromagnetic interaction is perhaps the most fundamental macroscopic quantum system.
		However, it is possible to “switch off” the macroscopic quantum behaviour of the spin 1/2 chain: applying a large magnetic field restores the classical individual of compass needles.
		The entirely altered excitation spectrum at large magnetic fields reflects the different character of the ferromagnetic and the antiferromagnetic groundstate: the continuous excitation spectrum at zero field is due to free spinon pairs, the fingerprint of the macroscopic quantum ground state of the antiferromagnetic spin 1/2 chain.
	www.ill.fr /AR-01/p-26.htm (1218 words)

	Discipline of Chemistry - Honours & Post Graduate
		It is proposed to investigate these relations by performing density functional calculations on the systems to be studied followed by detailed analysis of the binding center using the atoms in molecules (AIM) method to study the properties of the bound atoms and their associated critical points in the electron density.
		A detailed investigation of the antiferromagnetic interaction between the copper centres in molecules containing acetate bridged binuclear copper units.
		Structural characterisation is needed to establish the actual geometry obtained and magnetic characterisation involves determination of the interactions between the magnetic centres.
	www.jcu.edu.au /fmhms/school/pms/chem/honours_postgrad (3163 words)

	Abstract 381
		Thus, two different types of exchange interactions are present within this cluster: a ferromagnetic interaction between the octahedral Co(II) ions and an antiferromagnetic interaction between the octahedral and the tetrahedral Co(II) ions.
		As a result of the single-ion anisotropy of the octrahedral Co(II) ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co spin cluster is anisotropic and is expressed as H = -2
		are the components of the exchange interaction between the octahedral and tetrahedral Co(II) ions.
	www.dcb.unibe.ch /groups/guedel/abs01/hug_a381.htm (491 words)

	Victor Yakovenko: Research in 1995 (Site not responding. Last check: 2007-10-27)
		We argue that the peak may occur due to spin-flip electron excitations across the superconducting gap that are enhanced by antiferromagnetic interaction between Cu spins.
		Radtke, A. Liechtenstein, V. Yakovenko, and S. Das Sarma, ``Antiferromagnetic Interactions and the Superconducting Gap Function: Where are the Nodes?'', Phys.
		``Antiferromagnetic Interactions and the Superconducting Gap Function: Where are the Nodes?'' and ``Neutron scattering and superconducting order parameter in
	www.glue.umd.edu /~yakovenk/reports/1995.html (410 words)

	ACNS Conference 2004
		For most heavy fermion compounds, which are based on Ce, Yb, or U, the nonmagnetic heavy Fermi liquid ground state is believed to be associated with the Kondo effect arising from an antiferromagnetic exchange interaction between conduction electron spins and magnetic moments of the R or A ions with partially-filled f-electron shells (Kondo lattice).
		This suggests that magnetic dipole moment fluctuations are responsible for the NFL behavior and mediate the pairing of superconducting electrons in at least some of these materials.
		Heavy fermion behavior has been observed in several Pr compounds with nonmagnetic Pr ionic ground states in the crystalline electric field that appears to be due to the interaction between the charges of the conduction electrons and Pr electric quadrupole moments.
	www.ncnr.nist.gov /acns/program/abstract/t2d1.html (314 words)

	Bursill_h04_98
		The spins are coupled to the lattice degrees of freedom (ions, or phonons) in that the antiferromagnetic interaction (superexchange) between neighbouring spins depends on the separation of the Cu ions on which they reside.
		In the second half of 1998 we moved onto the Peierls-Heisenberg model of spins interacting with phonons (the lattice).
		The advantage of the technique is that it keeps the size of the truncated Hilbert space fixed as the lattice is grown while retaining excellent accuracy for the eigenvalues and wavefunctions, e.g., for the spin-1 antiferromagnetic chain, the infinite lattice ground state energy density was found to machine precision.
	anusf.anu.edu.au /annual_reports/annual_report98/Appendix_B/E_Bursill_h04_98.html (1836 words)

	Theses from Uppsala University : 2098 - Magnetism of manganites, semiconductors and spin glasses
		Due to random distribution of manganese in a Ag(Mn) alloy, competing ferromagnetic and antiferromagnetic interaction appears, yielding magnetic frustration and the appearance of a spin glass phase at low temperature.
		For an optimum doping x, a ferromagnetic order is established, and large changes of their electrical resistance with an applied magnetic field are observed; a magnetoresistance which can be tailored by adding oriented grain boundaries in thin films of these materials.
		The Manganese appears in the system as Mn and Mn, and both ferromagnetic and antiferromagnetic interaction is mediated by the charge carriers along the Mn-O-Mn bonds of the perovskite structure.
	publications.uu.se /theses/abstract.xsql?dbid=2098 (373 words)

	Physik: DPG Tagungen - Sitzung MA 21
		Since the copper triangles are coupled via hydrogen bonds, which naively are assumed to be weak exchange pathways, one expects that the chain shows a pronounced plateau at 1/3 of the saturation magnetization.
		The observed magnetization and susceptibility curves are successfully interpreted by a theoretical model, in which the inter- and intra-triangle exchange parameters are of similar size.
		For this material, as result of the Dzyaloshinskii-Moriya interaction and a staggered g-tensor, the ground state is characterized by an anisotropic field induced spin excitation gap and a staggered magnetization.
	www.dpg-tagungen.de /archive/2004/ma_21.html (1206 words)

	Cluster magnetism (Site not responding. Last check: 2007-10-27)
		Magnetic interaction has its origin in the electrostatic interaction: In a magnetic metal the ions have total spin and the exchange interaction between electrons determine the magnetic order.
		We have applied the Ising model and the Heisenberg model for studying the size-dependence of magnetism in ferromagnetic[1] and antiferromagnetic clusters[2].
		In the classical limit of the Heisenberg model with antiferromagnetic exchange interaction, a phenomenon analogous to zero-temperature phase transitions can be observed in certain clusters.
	www.phys.jyu.fi /research/clusters/magn.htm (274 words)

	093012pe
		Curie-Weiss temperature is related to the strength of antiferromagnetic interaction.
		On the other hand, with Sr and Mn further substitution for La and Fe antiferromagnetic interaction is promoted by increasing the proportion of Mn -O-Mn Therefore, the resistivity evidently is enhanced.
		The electrical behaviors of all specimens demonstrate insulator and the electrical resistivity increases with Mn and Sr ions doped.
	china.chemistrymag.org /cji/2007/093012pe.htm (1564 words)

	[No title] (Site not responding. Last check: 2007-10-27)
		The effect is due to second order interactions as in NMR when chemical shifts and coupling constants are of comparable magnitudes.
		The exchange interactions were all measured with a SQUID magnetometer.
		Interactions are possible for the Mo dimers over very large numbers of intervening bonds in the spacer.
	www.chm.bris.ac.uk /emr/Conferences/Mo (613 words)

	PASPS III Conference: Poster Session
		The shape of the line and its width indicate exchange interaction between Mn^2+ ions, which form pairs and other clusters for actual Mn concentration.
		Small ferromagnetic (FM) and antiferromagnetic (AFM) contributions to PM magnetization were also observed.
		Such beavior reflects the antiferromagnetic interaction between Mn ions and confirms results of EPR.
	www.sainc.com /pasps3/agendaposterView.asp?paperID=65 (438 words)

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