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Universal Sequence of the Ground States and Energy Level Ordering in Frustrated Antiferromagnetic Rings with a Single Bond Defect

100%
Antkowiak M., Florek W., Kamieniarz G.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
890-892
EN
The universal sequence of the ground states for antiferromagnetic frustrated rings with the odd number of the local spins s and a single bond defect α described by the isotropic Heisenberg Hamiltonian is discussed. The Lieb-Mattis energy level ordering in a pentanuclear ring is revealed and the arising magnetisation steps are demonstrated.
2
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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.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
411-413
EN
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
3
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Zero Temperature Magnetic Frustration in Nona-Membered s=3/2 Spin Rings with Bond Defect

100%
Antkowiak M., Kozłowski P., Kamieniarz G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1102-1104
EN
Zero-temperature limits of the local and global thermodynamic quantities in the nine-membered antiferromagnetic s=3/2 spin ring are investigated by means of numerical exact diagonalization. An anisotropic Heisenberg model with tunable bond defect reflecting continuously varying topology (from closed to open ring) is exploited. The frustrated and non-frustrated phases are identified in the ground-state phase diagram determined by a bond-defect strength and magnetic field. Near the phase boundaries significance of the thermal fluctuations affecting the estimates of the local magnetic quantities found earlier at T=1 K is revealed. For the global quantities the effects of thermal fluctuations are found much weaker. A sequence of the local magnetic moments is analysed and their experimental verification at the edges of the non-frustrated and within the entire frustrated phase is suggested at sufficiently low temperature.
4
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Modeling of the Experimental Molecular-Based Ring-Shaped Nanomagnets

76%
Antkowiak M., Kozłowski P., Musiał G., Florek W., Kamieniarz G., Esposito F.
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issue 5
965-966
EN
Quantum transfer matrix technique and numerically exact diagonalization method are applied to the Heisenberg spin systems to model ring-shaped molecules. Two cases are investigated: (i) a dozen of S = 1 spins with additional biquadratic exchange and (ii) a dimetallic molecule Cr_7Cd, where it is assumed that exchange anisotropy is determined in a local coordination system. In the latter case the calculated susceptibility is compared with experimental results.
5
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Anisotropy, Geometric Structure and Frustration Effects in Molecule-Based Nanomagnets

52%
Kamieniarz G., Kozłowski P., Antkowiak M., Sobczak P., Ślusarski T., Tomecka D., Barasiński A., Brzostowski B., Drzewiński A., Bieńko A., Mroziński J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
992-998
EN
In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n → ∞) frustration can be considered as the opposite to bipartiteness in the odd numbered (3 ≤ n ≤ 9) s = 3/2 quantum spin rings. We analyse the influence of exchange interactions and anisotropy on magnetic susceptibility of bimetallic (S = 3/2, s = 1/2) chains composed of Cu ions linked to different 3d ions by fitting experimental data. We reach the remarkable consistency of the density functional theory estimates of the magnetic couplings in Cr_8 molecule and provide strong support to the spin models exploited in the literature.
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