Approximate Approach to Magnetic and Thermodynamic Properties of Mixed Spin (1/2-S) Chains with AB and AB2 Topology

R. Pełkaa and D. Pinkowiczb aThe Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, E. Radzikowskiego 152, 31-342 Kraków, Poland bFaculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland

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Motivated by the rapid development in the synthesis of novel molecule-based magnets, we have investigated magnetic and thermodynamic properties of mixed spin (s-S) exchange coupled chains displaying a simple linear AB or a knotted AB2 arrangement. Approximate approach for s = 1/2 and S ≥ 5/2, treating at an intermediate step spin S operator as a commuting variable and using the transfer matrix technique, is used. Susceptibility, magnetization and heat capacity of both spin systems are evaluated numerically from the corresponding free energy for S = 5/2. Uniform: ferromagnetic and antiferromagnetic couplings are discussed. The procedure reproduces the right values of saturation magnetization and the entropy content of the systems, corroborating its correctness. χ T curves are shown to depend crucially on the μB H/J ratio. For zero-field heat capacity a double-peak structure is revealed for the AB chain, whereas for the AB2 chain only one broad anomaly is observed.

DOI: 10.12693/APhysPolA.118.959 PACS numbers: 75.10.Pq, 71.70.Gm, 75.30.Cr, 75.40.Cx