Tsoufis Theodoros, Tomou Aphrodite, Gournis Dimitrios, Douvalis Alexios P, Panagiotopoulos Ioannis, Kooi Bart, Georgakilas Vasilios, Arfaoui Imad, Bakas Thomas
Department of Materials Science and Engineering, University of Ioannina, GR-45110, Ioannina, Greece.
J Nanosci Nanotechnol. 2008 Nov;8(11):5942-51.
Multiwalled carbon nanotubes (MWCNTs) were used as nanotemplates for the dispersion and stabilization of FePt nanoparticles (NPs). Pre-formed capped FePt NPs were connected to the MWCNTs external surface via covalent binding through organic linkers. Free FePt NPs and MWCNTs-FePt hybrids were annealed in vacuum at 700 degrees C in order to achieve the L1(0) ordering of the FePt phase. Both as prepared and annealed samples were characterized and studied using a combination of experimental techniques, such as Raman and Mössbauer spectroscopies, powder X-ray Diffraction (XRD), magnetization and transmittion electron microscopy (TEM) measurements. TEM measurements of the hybrid sample before annealing show that a fine dispersion of NPs along the MWCNTs surface is achieved, while a certain amount of free particles attached to each other in well connected dense assemblies of periodical or non-periodical particle arrangements is also observed. XRD measurements reveal that the FePt phase has the face-centered cubic (fcc) disordered crystal structure in the as prepared samples, which is transformed to the face-centered tetragonal (fct) L1(0) ordered crystal structure after annealing. An increase in the average particle size is observed after annealing, which is higher for the free NPs sample. Superparamagnetic phenomena due to the small FePt particle size are observed in the Mössbauer spectra of the as prepared samples. Mössbauer and magnetization measurements of the MWCNTs-FePt hybrids sample reveal that the part of the FePt particles attached to the MWCNTs surface shows superparamagnetic phenomena at RT even after the annealing process. The hard magnetic L1(0) phase characteristics are evident in the magnetization measurements of both samples after annealing, with the coercivity of the hybrid sample over-scaling that of the free NPs sample by a factor of 1.25.
多壁碳纳米管（MWCNTs）被用作纳米模板，用于分散和稳定FePt纳米颗粒（NPs）。预先形成的封端FePt NPs通过有机连接体经由共价键合连接到MWCNTs的外表面。将游离的FePt NPs和MWCNTs-FePt杂化物在真空中于700℃退火，以实现FePt相的L1(0)有序化。使用拉曼光谱和穆斯堡尔光谱、粉末X射线衍射（XRD）、磁化和透射电子显微镜（TEM）测量等多种实验技术对制备态和退火态样品进行了表征和研究。退火前杂化样品的TEM测量表明，NPs沿MWCNTs表面实现了精细分散，同时还观察到一定数量的游离颗粒在周期性或非周期性颗粒排列的连接紧密的组装体中相互附着。XRD测量表明，制备态样品中FePt相具有面心立方（fcc）无序晶体结构，退火后转变为面心四方（fct）L1(0)有序晶体结构。退火后观察到平均粒径增加，游离NPs样品的粒径增加幅度更大。在制备态样品的穆斯堡尔谱中观察到由于FePt粒径小而产生的超顺磁现象。MWCNTs-FePt杂化样品的穆斯堡尔和磁化测量表明，即使在退火过程后，附着在MWCNTs表面的部分FePt颗粒在室温下仍表现出超顺磁现象。退火后两个样品的磁化测量中硬磁L1(0)相特征明显，杂化样品的矫顽力比游离NPs样品高1.25倍。
