Cooperative spin-crossover-like transitions in the inhomogeneous chain of exchange clusters

• Published in: Physical chemistry chemical physics : PCCP 2013-06, Vol.15 (24), p.9931-9939
• Main Author: Morozov, Vitaliy A
• Format: Article
• Language: English
• Subjects: Approximation; Breathing; Chains; Clusters; Crystals; Magnetic permeability; Mathematical analysis; Mathematical models
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp50689d

A statistical theory of temperature-induced spin-crossover-like transitions has been developed for spin chains with a few exchange clusters in a unit cell. Using static magnetic susceptibility measurements, a general expression for the effective magnetic moment eff of exchange clusters is obtained for an arbitrary structure of cluster terms. For heterospin Cu(hfac) 2 L R complexes (breathing crystals) with a head-to-head chain motif, a two-point approximation for a partition function of the JahnTeller Cu +2 paramagnetic center (spin 1/2) is suggested. Theoretical results are compared with available experimental data on thermal spin-crossover-like transitions in the breathing crystal compounds. It is shown that the model developed is able to successfully describe both of the cases of smooth and abrupt (cooperative) spin transitions for chains of three-spin exchange clusters. Spin-crossover-like transitions of a new type with step-wise changes in a positive exchange integral are predicted. A theory of cooperative spin transitions for exchange cluster chains is developed to describe the magnetic properties of breathing crystal compounds.