Several metal–radical alternating chains ([Co(hfac)2(CnPNN)]) were prepared, and their crystal structures and magnetic properties were systematically studied, where CnPNN stands for a phenylnitronyl nitroxide ligand having a linear Cn alkoxy group at the ortho or para position. X-ray crystal structure analysis was successfully performed for [Co(hfac)2(p-C5PNN)] (p-5). The chain structure is similar to those of the known p-butoxy and o-ethoxy derivatives. Compound p-5 showed a very large coercive field of 51 kOe (4.1 MA m−1) and a saturation magnetization of 9.7 × 103 erg Oe−1 mol−1 at 6 K. o-Propoxy and o-pentoxy derivatives also exhibited large coercive fields of 50–54 kOe at 5–6 K. The activation energies of magnetization reorientation for the present compounds were estimated to be as large as 290–360 K from Arrhenius analysis using ac susceptibility data. In a temperature range of ca. 10–40 K, all of the present compounds behaved as very soft magnets, as indicated by no hysteresis in the ferromagnetic M–H curves. We propose a mechanism for the drastic soft–hard switch. The hard character grows immediately after freezing of the spin dynamics owing to the strong magnetic anisotropy.
制备了几种
金属自由基交替链([Co(hfac)2(Cn
PNN)]),并系统研究了它们的晶体结构和磁性能,其中Cn
PNN代表邻位或邻位具有直链Cn烷氧基的苯基
硝酰基硝基氧
配体。对位。成功对 [Co(hfac)2(p-C5
PNN)] (p-5) 进行了 X 射线晶体结构分析。链结构与已知的对丁氧基和邻乙氧基衍
生物的链结构相似。化合物 p-5 在 6 K 时表现出非常大的矫顽磁场 51 kOe (4.1 MA m−1) 和 9.7 × 103 erg Oe−1 mol−1 的饱和磁化强度。邻丙氧基和邻戊氧基衍
生物也表现出很大的磁化强度。 5-6 K 时的矫顽磁场为 50-54 kOe。根据使用交流磁化率数据的阿伦尼乌斯分析,本发明化合物的磁化重新取向的活化能估计高达 290-360 K。在约的温度范围内。在 10–40 K 下,所有现有化合物都表现得非常软,正如
铁磁 M–H 曲线中没有磁滞现象所表明的那样。我们提出了一种彻底的软硬切换机制。由于强磁各向异性,自旋动力学冻结后,硬特性立即增长。