Random mixed-metal Co1-xNix single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges

This paper reports the magnetic properties of a series of isomorphous metal-organic frameworks based on random heterometallic Co1-xNix chains with simultaneous azide, carboxylate and tetrazolate bridges. All the mixed-metal compounds show intrachain FM interactions, field-induced metamagnetism, and SCM-like slow magnetic relaxation. These behaviors are quite different from the parent Co(II) and Ni(II) materials, and even a small amount of metal replacement can cause significant magnetic changes. The static properties such as AF ordering, metamagnetic critical field and the hysteresis parameters show complicated composition dependence. Most interestingly, the mixed-metal systems can show a higher blocking temperature than the Co(II) compound, suggesting that the randomly distributed metal ions have synergistic effects on slow relaxation of magnetization. This is phenomenologically associated with the competitive effects of Delta(tau) and tau(o).