Direct evidence of exchange interaction dependence of magnetization relaxation in a family of ferromagnetic-type single-chain magnets

Abstract

Three Mn2Ni chains having the same repeating motif,[–MnIII–ON–NiII–NO–MnIII–(OPh)2–]n, possessing a structural C2 axis on the NiII ion and an inversion center at the midpoint of MnIII– (OPh)2–MnIII have beensynthesized:[Mn2(saltmen)2Ni(L)2(py)2](A)(saltmen22=N,N9–(1,1,2,2-tetramethylethylene)bis(salicylideneiminate); L = 1-methylimidazole-2-aldoximate (miao2), A = ClO4 2, 1; PF6 2, 2; L = 1-ethylimidazole-2-aldoximate (eiao2), A = ClO4 2, 3). Due to the strong antiferromagnetic interaction (J/kB # 219 K) between the MnIII and NiII ions via the –ON– linkage and the weak ferromagnetic interaction (J9/kB = +0.43 to +0.49 K) between the [Mn–ON– Ni–NO–Mn] trimer units via the –(OPh)2– linkage in addition to the strong anisotropy of the trimer unit (D/kB = 22.6 to 23.0 K), all three compounds can be viewed at low temperatures as chains of ferromagnetically coupled Ising-like anisotropic ST = 3 units. The combination of DC and AC susceptibility measurements revealed their single-chain magnet behavior (t0 # 1 6 10210 s, D/kB # 59 K). The observed energy barrier (D) is smaller than D/kB # 70 K found in the original series of MnIII 2Ni single-chain magnets possessing D/kB#22.5 K and J9/kB # +0.7 K, and is significantly larger than D/kB # 21 K of the MnIII 2Ni single-molecule magnets possessing D/kB = 22.4 K reported previously. The present report is the first systematic investigation of the linear exchange coupling (J9) dependence of the magnetization relaxation in a family of compounds including related Mn2Ni single-chain magnets and single-molecule magnets.