Topology of exchange interactions in copper-nitroxide based molecular magnets studied by EPR

Abstract

Switchable copper-nitroxide based molecular magnets Cu(hfac)₂L^R (‘breathing crystals’) have one-dimensional (1D) polymer-chain structure and 1D magnetic motif; however, the directions of polymer and magnetic chains in the crystal do not coincide. In this work we report the detailed electron paramagnetic resonance (EPR) study of the topology of intercluster exchange interactions forming the magnetic chains in a series of breathing crystals. The obtained results provide unambiguous manifestation of 1D magnetic behaviour, which degree correlates with the magnitude of intercluster exchange interaction. Analysis of experimental angular-dependent EPR data allowed us to determine relative orientations of magnetic chains with respect to polymer chains. The obtained angle between them is ≈40–46° for three studied compounds. The comparison of EPR and x-ray diffraction data confirms that 1D magnetic chains are formed by interacting adjacent spin triads of neighbouring polymer chains.

Keywords:

• EPR
• molecular magnetism
• 1D magnets
• copper
• nitroxides

Acknowledgements

This work was supported by the Russian Foundation for Basic Research (Nos. 11-03-00158, 12-03-33010, 12-03-31184 and 12-03-31396), the RF President's Grant (MK-1662.2012.3, MK-868.2011.3, Nsh-2429.2012.3), RAS (No. 5.1.1) and The Ministry of Education and Science of Russian Federation (projects 8436 and 8456).