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4 Acta Physica Polonica A

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Highly Degenerated Ground States in Some Rings Modeled by the Ising Spins with Competing Interactions

100%

Florek W. , Antkowiak M. , Kamieniarz G. , Jaśniewicz-Pacer K.

nr 3

411-413

We discuss three Ising ring systems with competing interactions which are analogs of quantum systems and we show that they exhibit similar properties. In particular, the archetypal system of three antiferromagnetically coupled spins s has two magnetically degenerated ground states with |M|=s, when 0

Structural and Magnetic Properties of Co Thin Films on Au(111) Substrates

100%

Walczak A. , Ślusarski T. , Lehmann-Szweykowska A. , Kamieniarz G.

nr 3

653-659

The structural and magnetic properties of thin Co films grown on Au(111) substrates are investigated using ab initio local-spin-density calculations in the generalized gradient approximation. It is shown that a large lattice intermismatch between Co and Au(111) leads to a strong contraction of the interlayer distances within the Co layer, which adopts either the hexagonal close-packed (α-phase) or the face-centered cubic (β-phase) structure of bulk Co. Magnetic moments in the Co layer are increased beyond their value in bulk Co, the enhancement being strongest at the free surface and at the Co/Au interface, and more modest in the central part of the adlayer. Moderating influence of capping Ag layers on the structure and the magnetic properties of the films has also been considered. It is shown that Ag capping reduces the magnetic moments in comparison to uncovered Co/Au systems.

DFT Estimation of Exchange Coupling Constant of Cr₈ Molecular Ring using the Hybrid Functional B3LYP

100%

Wojciechowski M. , Brzostowski B. , Kamieniarz G.

nr 2

407-409

A study of electronic and magnetic properties of an octametallic chromium-based homonuclear molecule Cr₈F₈(CO₂-C(CH₃)₃)₁₆ is presented, using density functional theory (DFT) approach and linearized augmented plane wave (LAPW) method with Perdew, Burke and Ernzerhof (PBE) and Becke 3-term correlation (B3LYP) functionals. The exchange coupling parameters between transition metals ions are extracted, taking into account two different (ferro- and antiferromagnetic) spin configurations. The value J=3.1 meV found for the hybrid B3LYP functional improves significantly the one obtained for the PBE functional and gives an evidence for the superiority of the former in simulation of molecular nanomgnets. Moreover, the hybrid functional yields excellent spin density localisation, an enhancement of the HOMO-LUMO gaps and the value 2.81 μ_B of magnetic moment at the chromium centre in good agreement with experiment.

Mapping of the DFT Spin Configuration Energies of Cr8Cd Molecular Ring onto the Energy Structure of Falicov-Kimball Model

100%

Wojciechowski M. , Brzostowski B. , Lemański R. , Kamieniarz G.

nr 2

410-412

A comprehensive study of electronic and magnetic properties of a recently synthesized nonametalic chromium-based heteronuclear molecule Cr₈CdF₉(O₂C-C(CH₃)₃)₁₈ is presented, using DFT and Falicov-Kimball (FK) model approach. The magnetic moments are calculated and the spin charge density map is discussed. The exchange coupling parameters between transition metals ions are extracted, taking into account all the nonequivalent spin configurations. It is demonstrated that the energies of the spin configurations can be reproduced by the FK model with a set of parameters consistent with that for the parent Cr8 molecule. For molecular ring considered, the ground state corresponds to the antiferromagnetic configuration and the ferromagnetic configuration yields the highest energy.

Magnet with Ferromagnetic Nearest-Neighbor and Antiferromagnetic Next-Nearest-Neighbor Exchange Interactions

63%

Szymczak R. , Szymczak H. , Kamieniarz G. , Szukowski G. , Jaśniewicz-Pacer K. , Florek W. , Maltsev V. , Babonas G.

Acta Physica Polonica A

2009

tom 115

nr 5

925-930

Magnetic properties of Pb[Cu(SO_4)(OH)_2] (linarite) natural single crystals were studied by magnetization and specific heat measurements. The angular dependences of magnetization were revealed which correlated with the regularities of the crystal structure. At about 2.8 K this quasi-one-dimensional Heisenberg system undergoes a phase transition to the long-range antiferromagnetic order with antiparallel magnetic moments aligned probably along the b-axis. The antiferromagnetic order is evidenced by the metamagnetic transition and pronounced λ-type anomaly at T_N in the specific heat. Using phenomenological modeling based on a quantum transfer-matrix method, we argue that at higher temperatures linarite is a quasi-one-dimensional system with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions.