Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Nano Lett. 2012 Jan 11;12(1):246-51. doi: 10.1021/nl2034514. Epub 2011 Dec 5.
Monodisperse 35 nm FeO nanoparticles (NPs) were synthesized and oxidized in a dry air atmosphere into core/shell FeO/Fe(3)O(4) NPs with both FeO core and Fe(3)O(4) shell dimensions controlled by reaction temperature and time. Temperature-dependent magnetic properties were studied on FeO/Fe(3)O(4) NPs obtained from the FeO NPs oxidized at 60 and 100 °C for 30 min. A large exchange bias (shift in the hysteresis loop) was observed in these core/shell NPs. The relative dimensions of the core and shell determine not only the coercivity and exchange field but also the dominant reversal mechanism of the ferrimagnetic Fe(3)O(4) component. This is the first time demonstration of tuning exchange bias and of controlling asymmetric magnetization reversal in FeO/Fe(3)O(4) NPs with antiferromagnetic core and ferrimagnetic shell.
单分散 35nm 的 FeO 纳米颗粒（NPs）被合成出来，并在干燥的空气氛围中氧化，形成具有可控 FeO 核和 Fe(3)O(4)壳尺寸的核/壳 FeO/Fe(3)O(4) NPs，其尺寸由反应温度和时间控制。在 60 和 100°C 下氧化 30 分钟得到的 FeO NPs 上研究了温度依赖性的磁性。在这些核/壳 NPs 中观察到了大的交换偏置（磁滞回线的移动）。核和壳的相对尺寸不仅决定了矫顽力和交换场，还决定了铁磁性 Fe(3)O(4)组分的主要反转机制。这是首次在具有反铁磁核和铁磁壳的 FeO/Fe(3)O(4) NPs 中调谐交换偏置和控制非对称磁化反转的演示。
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