Kim Taehun, Lim Sumin, Hong Jaeyoung, Kwon Soon Gu, Okamoto Jun, Chen Zhi Ying, Jeong Jaehong, Kang Soonmin, Leiner Jonathan C, Lim Jung Tae, Kim Chul Sung, Huang Di Jing, Hyeon Taeghwan, Lee Soonchil, Park Je-Geun
Center for Correlated Electron Systems, Institute for Basic Science, Seoul, 08826, Korea.
Department of Physics & Astronomy, Seoul National University, Seoul, 08826, Korea.
Sci Rep. 2018 Mar 23;8(1):5092. doi: 10.1038/s41598-018-23456-6.
Most interesting phenomena of condensed matter physics originate from interactions among different degrees of freedom, making it a very intriguing yet challenging question how certain ground states emerge from only a limited number of atoms in assembly. This is especially the case for strongly correlated electron systems with overwhelming complexity. The Verwey transition of FeO is a classic example of this category, of which the origin is still elusive 80 years after the first report. Here we report, for the first time, that the Verwey transition of FeO nanoparticles exhibits size-dependent thermal hysteresis in magnetization, Fe NMR, and XRD measurements. The hysteresis width passes a maximum of 11 K when the size is 120 nm while dropping to only 1 K for the bulk sample. This behavior is very similar to that of magnetic coercivity and the critical sizes of the hysteresis and the magnetic single domain are identical. We interpret it as a manifestation of charge ordering and spin ordering correlation in a single domain. This work paves a new way of undertaking researches in the vibrant field of strongly correlated electron physics combined with nanoscience.
凝聚态物理中大多数有趣的现象都源于不同自由度之间的相互作用，这使得一个非常有趣但具有挑战性的问题是，在仅由有限数量原子组成的体系中，某些基态是如何出现的。对于具有极大复杂性的强关联电子系统来说尤其如此。FeO的韦尔维转变就是这类情况的一个经典例子，自首次报道以来，其起源在80年后仍然难以捉摸。在此我们首次报道，FeO纳米颗粒的韦尔维转变在磁化强度、Fe核磁共振和X射线衍射测量中表现出尺寸依赖的热滞现象。当尺寸为120 nm时，热滞宽度达到最大值11 K，而对于块状样品则降至仅1 K。这种行为与磁矫顽力非常相似，并且热滞和磁单畴的临界尺寸相同。我们将其解释为单畴中电荷有序和自旋有序相关性的一种表现。这项工作为在强关联电子物理学与纳米科学相结合的活跃领域开展研究开辟了一条新途径。
