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首页> 外文期刊>Journal of geophysical research. Solid earth: JGR >Magnetic characterization of noninteracting, randomly oriented, nanometer-scale ferrimagnetic particles
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Magnetic characterization of noninteracting, randomly oriented, nanometer-scale ferrimagnetic particles

机译：非相互作用，随机取向，纳米级亚铁磁性粒子的磁性表征

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Studying the magnetic properties of ultrafine manometer-scale ferrimagnetic particles (<10 nm) is vital to our understanding of superparamagnetism and its applications to environmental magnetism, biogeomagnetism, iron biomineralization, and biomedical technology. However, magnetic properties of the ultrafine nanometer-sized ferrimagnetic grains are very poorly constrained because of ambiguities caused by particle magnetostatic interactions and unknown size distributions. To resolve these problems, we synthesized magnetoferritins using the recombinant human H chain ferritin (HEM). These ferrimagnetic HFn were further purified through size exclusion chromatography to obtain monodispersed ferrimagnetic HFn. Transmission electron microscopy revealed that the purified ferrimagnetic HFn are monodispersed and each consists of an iron oxide core (magnetite or maghemite) with an average core diameter of 3.9 ± 1.1 mm imbedded in an intact protein shell. The R value of the Wohlfarth-Cisowski test measured at 5 K is 0.5, indicating no magnetostatic interactions. The saturation isothermal remanent magnetization acquired at 5 K decreased rapidly with increasing temperature with a median unblocking temperature of 8.2 K. The preexponential frequency factor f_0 determined by AC susceptibility is (9.2 ± 7.9) x 10~(10) Hz. The extrapolated M_(rs)/M_s and B_(cr)/B_c at 0 K are 0.5 and 1.12, respectively, suggesting that the ferrimagnetic HFn cores are dominated by uniaxial anisotropy. The calculated effective magnetic anisotropy energy constant K_(eff) = 1.2 x 10~5 J/m~3, which is larger than previously reported values for bulk magnetite and/or maghemite or magnetoferritin and is attributed to the effect of surface anisotropy. These data provide useful insights into superparamagnetism as well as biomineralization of ultrafine ferrimagnetic particles.
机译：研究超细压力计级亚铁磁性颗粒（<10 nm）的磁性对于我们对超顺磁性及其在环境磁性，生物地磁，铁生物矿化和生物医学技术中的应用的理解至关重要。然而，由于颗粒静磁相互作用和未知的尺寸分布所引起的歧义性，极细的纳米级亚铁磁性晶粒的磁性能受到的约束非常有限。为了解决这些问题，我们使用重组人H链铁蛋白（HEM）合成了磁铁蛋白。通过尺寸排阻色谱法进一步纯化这些亚铁磁性HFn，以获得单分散的亚铁磁性HFn。透射电子显微镜显示，纯化的亚铁磁性HFn是单分散的，每个由铁氧化物核（磁铁矿或磁赤铁矿）组成，平均铁心直径为3.9±1.1毫米，嵌入完整的蛋白质壳中。在5 K下测得的Wohlfarth-Cisowski测试的R值为0.5，表明没有静磁相互作用。随着温度的升高，在5 K处获得的饱和等温剩余磁化强度迅速降低，中值解锁温度为8.2K。由AC磁化率确定的指数前频率因子f_0为（9.2±7.9）x 10〜（10）Hz。在0 K处外推的M_（rs）/ M_s和B_（cr）/ B_c分别为0.5和1.12，这表明亚铁磁性HFn磁芯以单轴各向异性为主。计算的有效磁各向异性能量常数K_（eff）= 1.2 x 10〜5 J / m〜3，大于先前报道的块状磁铁矿和/或磁赤铁矿或磁铁蛋白的值，并且归因于表面各向异性的影响。这些数据为超顺磁性以及超细亚铁磁性颗粒的生物矿化提供了有用的见识。

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