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

2007; Royal Society of Chemistry; Volume: 17; Issue: 19 Linguagem: Inglês

10.1039/b617493k

1364-5501

Ayumi Saitoh, Hitoshi Miyasaka, Masahiro Yamashita, Rodolphe Clérac,

Organic and Molecular Conductors Research

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 been synthesized: [Mn2(saltmen)2Ni(L)2(py)2](A)2 (saltmen2− = N,N′–(1,1,2,2-tetramethylethylene)bis(salicylideneiminate); L = 1-methylimidazole-2-aldoximate (miao−), A = ClO4−, 1; PF6−, 2; L = 1-ethylimidazole-2-aldoximate (eiao−), A = ClO4−, 3). Due to the strong antiferromagnetic interaction (J/kB ≈ −19 K) between the MnIII and NiII ions via the –ON– linkage and the weak ferromagnetic interaction (J′/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 = −2.6 to −3.0 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 (τ0 ≈ 1 × 10−10 s, Δ/kB ≈ 59 K). The observed energy barrier (Δ) is smaller than Δ/kB ≈ 70 K found in the original series of MnIII2Ni single-chain magnets possessing D/kB ≈ −2.5 K and J′/kB ≈ +0.7 K, and is significantly larger than Δ/kB ≈ 21 K of the MnIII2Ni single-molecule magnets possessing D/kB = −2.4 K reported previously. The present report is the first systematic investigation of the linear exchange coupling (J′) dependence of the magnetization relaxation in a family of compounds including related Mn2Ni single-chain magnets and single-molecule magnets.