Macroscopic behavior and microscopic magnetic properties of nanocarbon E. Lähderanta a,n , V.A. Ryzhov a,b , A.V. Lashkul a , D.M. Galimov a,c , A.N. Titkov a,d , V.V. Matveev a,e , M.V. Mokeev f , A.I. Kurbakov b , K.G. Lisunov a,g a Lappeenranta University of Technology, PO Box 20, FIN-53851 Lappeenranta, Finland b Petersburg Nuclear Physics Institute, NRC “Kurchatov Institute”, Orlova Coppice, Gatchina, Leningrad province 188300, Russia c South Ural State University, 454080 Chelyabinsk, Russia d A. F. Ioffe Physico-Technical Institute,194021 St. Petersburg, Russia e Saint-Petersburg State University, Saint-Petersburg 198504, Russia f Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia g Institute of Applied Physics ASM, Academiei Str., 5, MD 2028 Kishinev, Moldova article info Article history: Received 19 June 2014 Received in revised form 21 October 2014 Keywords: Nanocarbon Neutron diffraction NMR Magnetic properties abstract Here are presented investigations of powder and glass-like samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co. The neutron diffraction study reveals an amorphous structure of the samples doped with Au and Co, as well as the magnetic scattering due to a long-range FM order in the Co-doped sample. The composition and molecular structure of the sample doped with Au is clarified with the NMR investigations. The temperature dependence of the magnetization, M (T), exhibits large irreversibility in low fields of B ¼1–7 mT. M (B) saturates already above 2 T at high tem- peratures, but deviates from the saturation behavior below 50 (150 K). Magnetic hysteresis is observed already at 300 K and exhibits a power-law temperature decay of the coercive field, B c (T). The macro- scopic behavior above is typical of an assembly of partially blocked magnetic nanoparticles. The values of the saturation magnetization, M s , and the blocking temperature, T b , are obtained as well. However, the hysteresis loop in the Co-doped sample differs from that in other samples, and the values of B c and M s are noticeably increased. & 2014 Published by Elsevier B.V. 1. Introduction A broad variety of carbon-based materials attracts attention due to unusual magnetic properties, including ferromagnetic (FM) behavior with evidence for a possibility of a long-range magnetic order [1,2]. Some of them are characterized by FM Curie tem- perature, T C , lying above the room temperature [1–4]. Possible utilization of such materials stretches from spintronics and light magnets in technical devices to applications for biological and medical purposes [1,2]. Most known bulk modifications of carbon, as ordered graphite and diamond with negligible concentration of intrinsic defects, exhibit a pronounced diamagnetism [1,2,5]. However, introduction of additional defects has shown that the material acquires FM-like properties, which takes place e.g. in proton-irradiated graphite [2,6,7]. Generally, it is widely believed that unconventional magnetism of carbon materials is connected with formation of defects or disorder in an ordered host matrix [1,2]. On the other hand, possible role of magnetic impurities in triggering the FM order still cannot be excluded unambiguously [1,2], although evidence of a π-electron ferromagnetism in metal-free carbon samples has been established [8,9]. Hence, investigations of car- bon structures with metallic atoms, magnetic or not, which have been introduced in the material intentionally, is interesting ques- tion for clarification the role of such atoms in formation of the magnetic properties of the material, as well as for application purposes [7–13]. Intrinsic magnetism of carbon materials has been predicted also in extensive theoretical investigations. It has been shown a possibility of FM behavior on a graphite surface with negative Gaussian curvature [14], in a mixture of carbon atoms with alter- nation of sp 2 and sp 3 bonds [15], in the presence of the graphene zigzag edges [16,17] and in disordered graphite with randomly distributed single-atom defects, preserving the ordered stacking of the graphene layers [18]. A possibility of the ferrimagnetic order in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.10.104 0304-8853/& 2014 Published by Elsevier B.V. n Corresponding author. Fax: þ358 5 6212898. E-mail address: Erkki.Lahderanta@lut.fi (E. Lähderanta). Please cite this article as: E. Lähderanta, et al., Journal of Magnetism and Magnetic Materials (2014), http://dx.doi.org/10.1016/j. jmmm.2014.10.104i Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎