The results of a study of the dynamic (alternating current magnetic susceptibility) and static magnetic properties, as well as Fe Mössbauer spectrometry and ferromagnetic resonance of two-line ferrihydrite nanoparticle systems with varying intensities of magnetic interparticle interactions are reported. The strength of the magnetic interparticle interactions has been tuned by coating (with various degrees of coating) the ferrihydrite particles (2–4 nm in size and an average size ∼2.7 nm) of the initial synthetic sample by arabinogalactan. Also, a biogenic ferrihydrite sample (an average particle size of 2-nm) with a natural organic coating was studied and it has the weakest magnetic interparticle interactions among of all the samples. Relaxation times of the particle’s magnetic moment were determined by the data of static and dynamic magnetic susceptibilities and from analysis of Fe Mössbauer spectrometry. Based on the temperature dependences of the relaxation times, it has been concluded that the predominantly collective processes of freezing of the particle magnetic moments occur under the action of the magnetic interparticle interactions. It is shown that an important role in these processes is played by a magnetic subsystem of the surface spins of the particles. The effect of the interplay between the surface spin and magnetic moment subsystems on the static magnetic properties (low-temperature magnetic hysteresis loops) and the parameters of the microwave absorption line under the magnetic resonance conditions is discussed.

中文翻译：

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调节超细水铁矿纳米颗粒集合中颗粒间相互作用的磁性集体态形成

报道了具有不同磁性颗粒间相互作用强度的两线水铁矿纳米颗粒系统的动态（交流磁化率）和静态磁特性以及铁穆斯堡尔谱和铁磁共振的研究结果。通过用阿拉伯半乳聚糖涂覆（不同程度的涂覆）初始合成样品的水铁矿颗粒（尺寸为 2-4 nm，平均尺寸~2.7 nm），可以调节磁性颗粒间相互作用的强度。此外，还研究了具有天然有机涂层的生物水铁矿样品（平均粒径为 2 nm），它在所有样品中具有最弱的磁性颗粒间相互作用。粒子磁矩的弛豫时间由静态和动态磁化率数据以及铁穆斯堡尔谱分析确定。基于弛豫时间的温度依赖性，可以得出结论，颗粒磁矩冻结的主要集体过程是在磁性颗粒间相互作用的作用下发生的。结果表明，颗粒表面自旋的磁性子系统在这些过程中发挥着重要作用。讨论了表面自旋和磁矩子系统之间的相互作用对磁共振条件下静磁特性（低温磁滞回线）和微波吸收线参数的影响。