ABSTRACT In this study, the exchange bias effect (EBE) revealed by the HCP-FCC structural phase transformation in Cobalt nanoparticles (CoNPs) are modeled and investigated by using the Ising model within the framework of the Effective Field Theory developed by Kaneyoshi. CoNPs are mixed (indistinguishable HCP and FCC) phase at T < 0.36 and T > TcFCC. For the non-structural transformation, CoNPs exhibit no exchange bias effect (HEB = 0.0) and they have normal symmetric coercive field points. But, they have asymmetric coercive field points and they have an exchange bias field for the HCP → FCC transformation or the inverse (HCP ← FCC). Additionally, an intersection point (Hi) revealed by EBE is obtained between the irreversible M–H curve of the FCC and HCP phase (Hi = Hc1FCC = −0.39 and −0.13). Our results show that the exchange bias effect strongly depends on their irreversible structural phase transformations in the materials.

中文翻译：

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钴纳米粒子的 HCP 和 FCC 结构之间的不可逆结构转变揭示的交换偏置效应

摘要 在这项研究中，钴纳米粒子 (CoNPs) 中 HCP-FCC 结构相变揭示的交换偏置效应 (EBE) 是通过在 Kaneyoshi 开发的有效场理论框架内使用 Ising 模型进行建模和研究的。CoNP 在 T < 0.36 和 T > TcFCC 时混合（无法区分 HCP 和 FCC）相。对于非结构变换，CoNPs 没有交换偏置效应（HEB = 0.0）并且它们具有正常的对称矫顽场点。但是，它们具有不对称的矫顽场点，并且它们具有用于 HCP → FCC 变换或逆变换 (HCP ← FCC) 的交换偏置场。此外，在 FCC 和 HCP 相的不可逆 M-H 曲线之间获得了 EBE 显示的交点（Hi）（Hi = Hc1FCC = -0.39 和 -0.13）。