Magnetic phase separation and unusual scenario of its temperature evolution in porous carbon-based nanomaterials doped with Au and Co
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RYZHOV, Vyacheslav, LASHKUL, Alexander V., MATVEEV, Vladimir, MOLKANOV, P., KURBAKOV, Alexander, KISELEV, I., LISUNOV, Konstantin, GALIMOV, D., LÄHDERANTA, Erkki. Magnetic phase separation and unusual scenario of its temperature evolution in porous carbon-based nanomaterials doped with Au and Co. In: Journal of Magnetism and Magnetic Materials, 2018, vol. 445, pp. 84-94. ISSN 0304-8853. DOI: https://doi.org/10.1016/j.jmmm.2017.08.077
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Journal of Magnetism and Magnetic Materials
Volumul 445 / 2018 / ISSN 0304-8853

Magnetic phase separation and unusual scenario of its temperature evolution in porous carbon-based nanomaterials doped with Au and Co

DOI:https://doi.org/10.1016/j.jmmm.2017.08.077
CZU: 538.9

Pag. 84-94

Ryzhov Vyacheslav12, Lashkul Alexander V.2, Matveev Vladimir3, Molkanov P.1, Kurbakov Alexander31, Kiselev I.1, Lisunov Konstantin24, Galimov D.25, Lähderanta Erkki2
 
1 Petersburg Nuclear Physics Institute, NRC “Kurchatov Institute”,
2 Lappeenranta University of Technology,
3 Saint Petersburg State University,
4 Institute of Applied Physics, Academy of Sciences of Moldova,
5 South Ural State University
 
 
Disponibil în IBN: 22 februarie 2018


Rezumat

Two porous glassy carbon-based samples doped with Au and Co were investigated. The magnetization study as well as measurements of the nonlinear longitudinal response to a weak ac field (NLR) and electron magnetic resonance give evidences for a presence of magnetic nanoparticles (MNPs) embedded in paramagnetic/ferromagnetic matrix respectively, both samples being in magnetically phase-separated state at temperatures above 300 K. Matrix, forming by paramagnetic centers located in matrix outside the MNPs, reveals exchange interactions providing its ferromagnetic (FM) ordering below TC ≈ 210 K in Au-doped sample and well above 350 K in Co-doped one. For the former, NLR data suggest a percolation character of the matrix long-range FM order, which is mainly caused by a porous amorphous sample structure. Temperature dependence of the magnetization in the Au-doped sample evidences presence of antiferromagnetic (AF) interactions of MNPs with surrounding matrix centers. At magnetic ordering below TC these interactions promote origination of “domains” involving matrix fragment and surrounding MNPs with near opposite orientation of their moments that decreases the magnetostatic energy. On further cooling, the domains exhibit AF ordering below Tcr ∼ 140 K < TC, resulting in formation of a peculiar “ferrimagnet”. The porous amorphous structure leads to absence of translational and other symmetry features through the samples that allows canted ordering of magnetic moments in domains and in whole sample providing “canted ferrimagnetism”. At low temperatures Ttr ∼ 3 K, “order-oder” transition, evidencing the non-Heisenberg character of this magnetic material, occurs from ordering like “canted ferrimagnet” to FM alignment, which is stimulated by external magnetic field. The data for Co-doped sample imply the similar evolution of magnetic state but at higher temperatures above 350 K. This state exhibits more homogeneous arrangement of the FM nanoparticles and the FM matrix. Order-order transition occurs in it at higher Ttr ∼ 10–15 K as well and followed by formation of long-range FM ordering found earlier by neutron diffraction. Doping of carbon-based nanomaterials by magnetic metals provides advantages for their possible practical applications as Co-doped sample with higher TC (>350 K) and larger remanent magnetization evidences.

Cuvinte-cheie
Carbon-based materials, Magnetic ordering, Magnetic phase separation