Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK.
J Phys Condens Matter. 2010 Nov 3;22(43):436005. doi: 10.1088/0953-8984/22/43/436005. Epub 2010 Oct 11.
The structural and magnetic properties of 1.8 nm Co particles dispersed in a Mn matrix by co-depositing pre-formed mass-selected Co clusters with an atomic vapour of Mn onto a common substrate have been studied by using EXAFS (extended x-ray absorption fine structure), XMCD (x-ray magnetic circular dichroism), magnetometry, and theoretical modelling. At low Co volume fraction (5%) Co@Mn shows a significant degree of alloying and the well-defined particles originally deposited become centres of high Co concentration CoMn alloy that evolves from pure Co at the nanoparticle centre to the pure Mn matrix within a few nm. Each inhomogeneity is a core-shell particle with a Co-rich ferromagnetic core in contact with a Co-depleted antiferromagnetic shell. The XMCD reveals that the Co moment localized on the Co atoms within the Co-rich cores is much smaller than the ferromagnetic moment of the Co nanoparticles deposited at the same volume fraction in Ag. Electronic structure calculations indicate that the small magnitude of the core Co moment can be understood only if significant alloying occurs. Monte Carlo modelling replicates the exchange bias (EB) behaviour observed at low temperature from magnetometry measurements. We ascribe EB to the interaction between the ferromagnetic Co-rich cores and the antiferromagnetic Mn-rich shells.
通过将预先形成的质量选择的 Co 团簇与 Mn 的原子蒸气共沉积到共同基底上，在 Mn 基体中分散 1.8nm Co 颗粒的结构和磁性能已通过 EXAFS（扩展 X 射线吸收精细结构）、XMCD（X 射线磁圆二色性）、磁测量和理论建模进行了研究。在低 Co 体积分数（5%）下，Co@Mn 表现出明显的合金化程度，最初沉积的规则颗粒成为高 Co 浓度 CoMn 合金的中心，该合金从纳米颗粒中心的纯 Co 演化到几 nm 范围内的纯 Mn 基体。每个不均匀性都是一个具有富 Co 铁磁核的核壳颗粒，与 Co 耗尽的反铁磁壳接触。XMCD 表明，在 Co 富核内局域在 Co 原子上的 Co 矩远小于在相同体积分数沉积在 Ag 中的 Co 纳米颗粒的铁磁矩。电子结构计算表明，只有发生明显的合金化，才能理解核 Co 矩的小幅度。蒙特卡罗模拟复制了从磁测量中观察到的低温下的交换偏置（EB）行为。我们将 EB 归因于铁磁 Co 富核与反铁磁 Mn 富壳之间的相互作用。
