Lähderanta E, Lashkul A V, Lisunov K G, Zherebtsov D A, Galimov D M, Titkov A N
Department of Mathematics and Physics, Lappeenranta University of Technology, PO Box 20, FIN-53851 Lappeenranta, Finland.
J Nanosci Nanotechnol. 2012 Dec;12(12):9156-62. doi: 10.1166/jnn.2012.6779.
Magnetization M(T, B) of powder and glassy samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co, is investigated at temperatures T between - 3-300 K in magnetic fields B up to 5T. According to atomic force microscopy data, a system of carbon particles has a broad size distribution, given by the average and the maximum radii of -60 nm and - 110 nm, respectively. In low fields of B << B(K), where B(K) - 1T is the mean anisotropy field, M(T) exhibits large irreversibility or deviation of zero-field cooled and field-cooled magnetizations, which is suppressed completely at B > B(K). The dependence of M(B) saturates above B - 2T at T - 150-300 K and contains a large paramagnetic-like response below - 50-150 K. Hysteresis is observed already at 300 K and is characterized by a power-law temperature decay of the coercive field, B(c)(T). This is described by the exponent n approximately 0.8 and by the low-temperature values of B(c) (0) increasing from -36-53 mT in the undoped sample and those doped with Ag and Au, up to 80 mT in the Co-doped material, yielding the blocking temperatures T(b) approximately 400-580 K. Analysis of the experimental magnetization data above suggests distribution of the magnetization close to the surface of the particles, yielding a thickness of the near-surface layer, h, filled with localized magnetic moments, micro1 - microB, to be close to the average distance, a, between the moments, h approximately a - 1 nm. This is consistent with the origin of magnetism in nanocarbon being presumably due to intrinsic near-surface defects.
研究了含有碳纳米颗粒、未有意掺杂以及掺杂了银、金和钴的粉末和玻璃态样品在温度(T)介于(-3)至(300K)、磁场(B)高达(5T)时的磁化强度(M(T,B))。根据原子力显微镜数据，碳颗粒系统具有宽泛的尺寸分布，平均半径和最大半径分别为(-60nm)和(-110nm)。在(B\ll B(K))的低场中，其中(B(K) - 1T)是平均各向异性场，(M(T))表现出大的不可逆性或零场冷却和场冷却磁化强度的偏差，在(B > B(K))时这种偏差被完全抑制。在(T - 150 - 300K)时，(M(B))的依赖关系在(B - 2T)以上饱和，并且在(-50 - 150K)以下包含大的类似顺磁的响应。在(300K)时就观察到了磁滞现象，其特征是矫顽场(B(c)(T))的幂律温度衰减。这由指数(n)约为(0.8)以及(B(c)(0))的低温值来描述，在未掺杂样品以及掺杂银和金的样品中，(B(c)(0))从(-36 - 53mT)增加，在钴掺杂材料中高达(80mT)，得出阻塞温度(T(b))约为(400 - 580K)。对上述实验磁化强度数据的分析表明，磁化强度分布在颗粒表面附近，得出充满局域磁矩(\mu_1 - \mu_B)的近表面层厚度(h)接近磁矩之间的平均距离(a)，(h\approx a - 1nm)。这与纳米碳中磁性的起源大概是由于本征近表面缺陷是一致的。
