Magnetic properties of oleic acid/oleylamine coated magnetite nanoparticles of average diameter D=4, 6, 8, 10, and 12 nm are reported. The samples were characterized by transmission electron microscopy and x-ray diffraction (XRD) with XRD showing increasing disorder with decreasing D. Magnetization M vs temperature T data show the blocking temperature T_B decreasing with decreasing D from T_B=38 K for 12 nm to T_B=6.5 K for D=4 nm. The saturation magnetization M_s at 2 K also decreases from M_s=62 emu/g for 12 nm to M_s=17 emu/g for 4 nm but the coercivity at 2 K increases with a decrease in D. It is shown that M_s fits M_s=92(l-2d/D)~3 with d =0.68 nm for D>4 nm and d=0.S6 for D=4 nm. This equation is derived assuming a core-shell model with shell of thickness d consisting of disordered spins not contributing to M_s.
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机译:报道了油酸/油胺涂覆的平均直径d = 4,6,8,10和12nm的油酸/油胺涂覆磁铁矿纳米颗粒的磁性。通过透射电子显微镜和X射线衍射(XRD)表征样品,X射线衍射(XRD)显示随着降低的紊乱D.磁化M VS温度T数据显示阻塞温度T_B从T_B = 38K减小D减小12 nm至t_b d = 6.5 k for d = 4nm。 2 k的饱和磁化强度M_S也从M_S = 62 emu / g减少12nm至m_s = 17 emu / g 4nm,但在2k时的矫顽力随下降的减少而增加。显示M_s fits m_s = 92(L-2D / D)〜3具有D = 0.68nm的D> 4nm和d = 0.s6,对于d = 4nm。假设具有厚度D的壳体模型的核心壳模型导出了该等式,该核心壳模型由无序的旋转组成而没有贡献M_S。
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