Single-chain magnet features in 1D MnR_4TPP TCNE compounds

摘要

Molecular chains of antiferrimagnetically coupled Mn -ion (S = 2) and TCNE (tetracyanoethylene) radical moments (s = 1/2) show different behaviour depending on group R substituted to TPP (tetraphenylporphyrin) and on the substitution site. The compound with R = F in Ortho position is a Single-Chain Magnet (SCM) with blocking temperature T_b = 6.6K, while that with R = F in Meta position shows both blocking (T_b = 5.4 K) and magnetic ordering transition (T_c = 10 K). For bulky groups R = OC_nH_(2n+1), the magnetically ordered phase is observed (T_c ≈ 22 K), which does not however prevent slow relaxation at T <8 K. Magnetic hysteresis with coercive field H_c of 2 T at 2.3 K is like that of SCM. The frequency dependent AC susceptibility in the superimposed DC field reveals common features of all systems. The energy of intrachain ferromagnetic coupling between effective spin units 3/2, relevant at low temperatures, is determined for all compounds and the interchain dipolar coupling is estimated. It is concluded that slow relaxation is inherent for all quasi one-dimensional compounds and for the magnetically ordered ones shows up in the high enough magnetic field.