Hiroi Kosuke, Kura Hiroaki, Ogawa Tomoyuki, Takahashi Migaku, Sato Tetsuya
Department of Applied Physics & Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama, 223-8522, Japan.
J Phys Condens Matter. 2014 Apr 30;26(17):176001. doi: 10.1088/0953-8984/26/17/176001. Epub 2014 Apr 8.
The magnetic behavior of α-Fe/Au nanoparticle (NP) assemblies is studied over a very wide range of dipolar interactions among α-Fe NPs, by changing the volume density of the α-Fe NP. The assembly whose α-Fe NP density is lower than 0.1% exhibits typical superparamagnetic behavior. When Fe NP density exceeds 8.6% the magnetic dynamics changes to that resembling superspin glass. Moreover, NP assembly with highest Fe concentration (43%), whose dipolar interaction is enormously strong compared with previous studies, exhibits a two-stage magnetic transition, i.e., ferromagnetic and spin glass-like transitions at 385 K and around 150 K, respectively. Therefore, we first observed the reentrant spin glass-like magnetism at the limit of strong interaction in a close-packed NP assembly. Based on these observations, the magnetic phase diagram of the interacting α-Fe NP assembly is determined over a very wide range of interaction.
通过改变α-Fe纳米颗粒（NP）的体积密度，研究了α-Fe/Au纳米颗粒组装体在α-Fe NP之间非常广泛的偶极相互作用范围内的磁行为。α-Fe NP密度低于0.1%的组装体表现出典型的超顺磁行为。当Fe NP密度超过8.6%时，磁动力学转变为类似于超自旋玻璃的状态。此外，具有最高Fe浓度（43%）的NP组装体，其偶极相互作用与先前的研究相比非常强，表现出两阶段磁转变，即在385 K和150 K左右分别发生铁磁和自旋玻璃状转变。因此，我们首次在密堆积NP组装体的强相互作用极限下观察到重入自旋玻璃状磁性。基于这些观察结果，确定了相互作用的α-Fe NP组装体在非常广泛的相互作用范围内的磁相图。
