PROXIMITY EFFECTS AND CURIE TEMPERATURE ENHANCEMENT IN Co/EuS AND Fe/EuS MULTILAYERS

Two identical Co/EuS and Fe/EuS multilayers of six periods each and with individual layers of about 4 nm thick are grown by e-beam evaporation under ultrahigh vacuum conditions. The films show polycrystalline structure with a grain size limited by the individual layer thickness. Both multilayers consist of almost continuous layers with some roughness. The surface peak-to-peak roughness is about 4–5 nm. Magnetization measurements and calculations of the loops based on a Stoner–Wohlfarth-like model allow us to determine the direct antiferromagnetic exchange coupling constant between the 3d metal and EuS at 5 K. Both samples show strong enhancement of the Curie temperature of EuS up to at least 50 K with a EuS magnetization tail, which persists up to about 100 K. The J = 7/2 character of the EuS layers is shown to be responsible for the large Curie temperature enhancement.

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ESR effects of singlet–triplet mixing in radical pairs. Determination of the individual g tensors and the exchange coupling constant from spectral shifts due to off‐diagonal Zeeman terms

The Journal of Chemical Physics ◽

10.1063/1.445469 ◽

1983 ◽

Vol 78 (9) ◽

pp. 5413-5419 ◽

Cited By ~ 8

Author(s):

J. R. Byberg ◽

Nis Bjerre ◽

A. Lund ◽

P.‐O. Samskog

Keyword(s):

Exchange Coupling ◽

Coupling Constant ◽

Radical Pairs ◽

Spectral Shifts ◽

Exchange Coupling Constant ◽

The Individual

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Metal pyrazolate polymers. Part 2. Synthesis, structure, and magnetic properties of [Cu(4-Xpz)2]x polymers (where X = Cl, Br, Me, H; pz = pyrazolate)

Canadian Journal of Chemistry ◽

10.1139/v91-065 ◽

1991 ◽

Vol 69 (3) ◽

pp. 432-439 ◽

Cited By ~ 28

Author(s):

Martin K. Ehlert ◽

Steven J. Rettig ◽

Alan Storr ◽

Robert C. Thompson ◽

James Trotter

Keyword(s):

Exchange Coupling ◽

Structural Parameters ◽

Magnetic Data ◽

Antiferromagnetic Exchange ◽

Coupling Constant ◽

Orthorhombic Space Group ◽

Magnetic Exchange ◽

Linear Chains ◽

Green Form ◽

Reliable Methods

Novel and reliable methods for the synthesis of the polymers [Cu(4-Xpz)2]x (where X = H, Cl, Br, and Me; pz = pyrazolate) are presented. The X = Cl compound was obtained as green and brown forms. Single crystals of the polymers with X = Me and X = Cl (green form) suitable for X-ray analysis have been obtained. [Cu(4-Mepz)2]x and [Cu(4-Clpz)2]x are isomorphous, crystallizing with four formula units per unit-cell in the orthorhombic space group Ibam, a = 9.7436(6), 9.155(4), b = 12.6106(8), 12.968(6), and c = 7.7482(6), 7.717(5) Å, respectively, for the 4-Me and 4-Cl derivatives. The structures were refined by full-matrix least-squares procedures to R = 0.027 and 0.041 for 430 and 246 reflections with I ≥ 3σ(I), respectively. Magnetic susceptibility studies over the temperature range 2 to 300 K have revealed that all the polymers exhibit very strong antiferromagnetic exchange between copper(II) centres in the extended linear chains. Discontinuities displayed in the susceptibility versus temperature plots suggest the presence of phase transitions at ~133 and ~108 K in the X = Cl (green form) and X = Br materials, respectively. The four compounds, X = H, Br, Me, and Cl (green form) also exhibit thermochromism over the 77 to 176 K region. The magnetic data have been analyzed employing an isotropic Heisenberg model for antiferromagnetic exchange in extended chain polymers. Values of the exchange coupling constant, J, for the room temperature forms of these materials are determined as −81, −105, −96, −104, and −88 cm−1 for 4-X = H, Br, Me, Cl (green form), and Cl (brown form), respectively. The magnitude of the exchange coupling is discussed in relation to structural parameters for the X = H, Me, and Cl (green form) compounds. Key words: copper(II) 4-substituted pyrazolate polymers, crystal structures, magnetic exchange.

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ChemInform Abstract: ESR EFFECTS OF SINGLET-TRIPLET MIXING IN RADICAL PAIRS. DETERMINATION OF THE INDIVIDUAL G TENSORS AND THE EXCHANGE COUPLING CONSTANT FROM SPECTRAL SHIFTS DUE TO OFF-DIAGONAL ZEEMAN TERMS

Chemischer Informationsdienst ◽

10.1002/chin.198333051 ◽

1983 ◽

Vol 14 (33) ◽

Author(s):

J. R. BYBERG ◽

N. BJERRE ◽

A. LUND ◽

P.-O. SAMSKOG

Keyword(s):

Exchange Coupling ◽

Coupling Constant ◽

Radical Pairs ◽

Spectral Shifts ◽

Exchange Coupling Constant ◽

The Individual

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Synthesis and characterization of the mixed valence Cu(l)/Cu(ll) 3,5-bis(trifluoromethyl)-pyrazolate complex, [Cu(ll)2Cu(l)(F6dmpz)5]

Canadian Journal of Chemistry ◽

10.1139/v97-057 ◽

1997 ◽

Vol 75 (5) ◽

pp. 491-498 ◽

Cited By ~ 15

Author(s):

Martin K. Ehlert ◽

Alan Storr ◽

David A. Summers ◽

Robert C. Thompson

Keyword(s):

Exchange Coupling ◽

Mixed Valence ◽

Direct Methods ◽

Magnetic Data ◽

Antiferromagnetic Exchange ◽

Coupling Constant ◽

Copper Metal ◽

X Ray ◽

R Value

The reaction of molten 3,5-bis(trifluoromethyl)pyrazole (F6dmpzH) with copper metal shot under an atmosphere of dioxygen yields the green trimetallic mixed valence [Cu(II)2Cu(1)(F6dmpz)5]. Crystals of [Cu(II)2Cu(I)(F6dmpz)5] are triclinic, a = 9.0557(2), b = 9.6164(2), c = 11.8874(3) Å, α= 105.406(1)°, β = 112.317(1)°, γ = 90.662(1)°, Z= 1, space group P͞1. The crystal structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R value of 0.0538 for 2591 reflections with I≥2σ(I). Magnetic susceptibility studies over the range 2–300 K reveal strong antiferromagnetic exchange coupling between the two copper(II) centers. Fits of the magnetic data to the Bleaney-Bowers equation for two interacting S= ½ centers gives the exchange coupling constant J = –235 cm–1. Key words: trimetallic, copper, 3,5-bis(trifluoromethyl)pyrazolates, X-ray structure, antiferromagnetism.

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Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

10.26434/chemrxiv.7976474.v2 ◽

2019 ◽

Author(s):

Xianghai Sheng ◽

Lee Thompson ◽

Hrant Hratchian

Keyword(s):

Density Functional Theory ◽

Exchange Coupling ◽

Density Functional ◽

Spin Crossover ◽

Coupling Constants ◽

Spin Projection ◽

Coupling Constant ◽

Projection Model ◽

Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

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