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Carbon-based magnetic nanomaterials
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite.

Abstract [sv]

Magnetism av kolbaserade material är ett utmanande område för både grundforskning och möjliga tillämpningar.

Vi presenterar studier med låg-dimensionella kolbaserade magnetiska system (fulleren-utspädda molekylära magneter, kolnanorör, grafit fluorid och nanoporösa kol) med hjälp av SQUID magnetometer, röntgendiffraktion och vibrerande spektroskopi, de senare tekniker som används som komplement instrument för att finna sambandet mellan den magnetiska uppträdande och strukturen hos proven.

I den första delen av avhandlingen är egenheter från magnetisering processen i linje filmer av kolnanorör med låg koncentration av järn diskuteras. Det visas att magnetism av sådana strukturer påverkas av kvantmekaniska effekter och anisotropin beteende är motsatsen till vad som observerats i kraftigt dopade nanorör.

I den tvåa delen är Mn12-baserade enda-molekyl magneter med olika karboxylsyror ligander och deras 1:1 fulleren-utspädda komplex studeras. Vi visar att magnetiska egenskaperna hos sådana system beror i hög grad på miljön, och i princip är det möjligt att utforma en magnet med önskvärda egenskaper. En av de studerade föreningarna visade en post blockeringstemperaturen för en enda molekylär magnet. Både fulleren-utspädda komplex visade "magnetisering utbildning" effekt i alternerande magnetfält och möjligheten att bevara magnetiskt moment.

Den tredje och fjärde delarna av avhandlingen är avsedda för inneboende magnetism av analys av olika bidrag till magnetisk susceptibilitet av metall-fritt kol-baserade system -inskjutna föreningar grafit fluorider och nanoporösa O2-eroderade grafit. Magnetiska egenskaperna hos dessa system är starkt beroende av strukturen, och kan fint avstämmas genom att man ändrar π-elektronsystem av grafit, i. e. med graden av fluorering av inskjutna föreningar och genom införandet av bor föroreningar till värd matris av nanoporösa grafit.

Ort, förlag, år, upplaga, sidor
Umeå University , 2012. , s. 77
Nyckelord [en]
carbon nanotube, fullerene, single molecular magnet, Mn12, graphite fluoride, nanoporous carbon, molecular magnetism, magnetic properties, SQUID magnetometry, x-ray diffraction, Raman spectroscopy
Nationell ämneskategori
Fysik
Forskningsämne
materialvetenskap
Identifikatorer
URN: urn:nbn:se:umu:diva-53568ISBN: 987-91-7459-396-9 (tryckt)OAI: oai:DiVA.org:umu-53568DiVA, id: diva2:513512
Disputation
2012-04-27, Naturvetarhuset, N200, Umeå Universitet, Umeå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2012-04-04 Skapad: 2012-04-02 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
Delarbeten
1. Magnetic properties of carbon nanotubes with low content of Fe
Öppna denna publikation i ny flik eller fönster >>Magnetic properties of carbon nanotubes with low content of Fe
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2010 (Engelska)Ingår i: Fullerenes, nanotubes, and carbon nanostructures (Print), ISSN 1536-383X, E-ISSN 1536-4046, Vol. 18, nr 4-6, s. 569-573Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Films of oriented carbon nanotubes containing different concentrations of ferrocene (0.5%, 1%, 1.5%, 2%, 2.5% and 5%) have been synthesized by CVD method and studied by means of SQUID and force microscopy. Strong dependence of magnetization process on nanotubes parameters is observed. Magnetic anisotropy of low-doped nanotubes is shown to have an easy magnetic axis perpendicular to the aligned nanotubes.

Nyckelord
Carbon nanotubes, low iron content, magnetic properties, Raman spectroscopy
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:umu:diva-37341 (URN)10.1080/1536383X.2010.488082 (DOI)000283555000039 ()
Anmärkning
Available online:27 Oct 2010. Proceedings of the 9th Biennial International Workshop “Fullerenes and Atomic Clusters”— Part 1Tillgänglig från: 2010-10-27 Skapad: 2010-10-27 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
2. Synthesis and magnetic properties of Mn-12-Based single molecular magnets with benzene and pentafluorobenzene carboxylate ligands
Öppna denna publikation i ny flik eller fönster >>Synthesis and magnetic properties of Mn-12-Based single molecular magnets with benzene and pentafluorobenzene carboxylate ligands
2011 (Engelska)Ingår i: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 24, nr 1-2, s. 855-859Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on the synthesis and magnetic properties of Mn12-based single molecular magnets (SMMs) with benzene and pentafluorobenzene carboxylate ligands. The changes in ligand structure are shown to have a decisive effect on the magnetic properties of the complexes produced. The compound with benzene demonstrates an unusual magnetic behavior, namely, temperature dependencies of magnetization taken under the zero-field-cooled and field-cooled conditions are split below 10 K and furthermore remnant magnetization and coercive force remain nonzero in this temperature range. In contrast, the compound with pentafluorobenzene displays the customary signatures of the blocking temperature at 3 K. The effect of ligand substitution was theoretically studied within the local density approximation taking into account on-site Coloumb repulsion. Calculation results confirm that the electronic structure and the magnetic exchange interactions between different Mn atoms strongly depend on the type of ligand.

Nyckelord
Mn12, SMM, agnetic properties
Identifikatorer
urn:nbn:se:umu:diva-44084 (URN)10.1007/s10948-010-1030-3 (DOI)
Tillgänglig från: 2011-05-19 Skapad: 2011-05-19 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
3. Preparation and magnetic properties of Mn-12 clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)(16)(H2O)(4)] and its tetraphenylphosphonium salts
Öppna denna publikation i ny flik eller fönster >>Preparation and magnetic properties of Mn-12 clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)(16)(H2O)(4)] and its tetraphenylphosphonium salts
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2012 (Engelska)Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 324, nr 18, s. 2746-2752Artikel i tidskrift (Övrigt vetenskapligt) Published
Abstract [en]

The new Mn12 magnetic clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)16(H2O)4] (1) and its singly (2) and doubly (3) reduced analogues as their tetraphenylphosphonium salts, have been synthesized and characterized by elemental analyses, Raman, ESI-MS spectra and magnetic measurements with a SQUID magnetometer. Unlike the known Mn12 oxocarboxylate clusters, which are very soluble in CH3CN or CH2Cl2, the complex 1 is not dissolved in organic solvents providing an indication for strong intermolecular interactions which lead to strong dipole-dipole interactions between clusters and affect the magnetic behaviour. The one-electron and two-electron reduced clusters (2, 3) contain the bulk counterion and dissolve in CH3CN. They show magnetic properties characteristic for anion Mn12 single-molecule magnets.

Nyckelord
Molecular magnetism, Manganese, Ligand design, Magnetic properties, Electrospray ionization mass spectrometry
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:umu:diva-53565 (URN)10.1016/j.jmmm.2012.03.061 (DOI)000304762400011 ()
Tillgänglig från: 2012-04-02 Skapad: 2012-04-02 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
4. Fullerene-induced magnetization training effect in single molecular magnet
Öppna denna publikation i ny flik eller fönster >>Fullerene-induced magnetization training effect in single molecular magnet
2010 (Engelska)Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 247, nr 11, s. 3018-3021Artikel i tidskrift (Refereegranskat) Published
Ort, förlag, år, upplaga, sidor
Weinheim: WILEY-VCH, 2010
Nyckelord
fullerene, magnetism, single molecular magnet, mn12
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fasta tillståndets fysik
Identifikatorer
urn:nbn:se:umu:diva-37961 (URN)10.1002/pssb.201000115 (DOI)000285798400089 ()
Tillgänglig från: 2010-11-19 Skapad: 2010-11-19 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
5. The magnetic memory effect in fullerene-containing single molecular magnets
Öppna denna publikation i ny flik eller fönster >>The magnetic memory effect in fullerene-containing single molecular magnets
2010 (Engelska)Ingår i: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 74, nr 10, s. 1426-1429Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We studied the influence of fullerenes on the properties of molecular magnets of the family of oxocarboxylate clusters of Mn12. A strong asymmetry in the hysteresis loop was observed for the first time. As opposed to the well-known effect of the displacement of a hysteresis loop along the magnetic field axis (the phenomenon of exchange bias), the observed effect of magnetic memory resides in the displacement along the vertical axis.

Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:umu:diva-37343 (URN)10.3103/S1062873810100308 (DOI)
Anmärkning
Proceedings of the XXI International Conference “Innovations in Magnetism and Magnetic Materials”. Original Russian Text © V.S. Zagainova, T.L. Makarova, N.G. Spitsyna, 2010, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2010, Vol. 74, No. 10, pp. 1486–1488.Tillgänglig från: 2010-10-27 Skapad: 2010-10-27 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
6. Structural evolution and magnetic properties of underfluorinated C2F
Öppna denna publikation i ny flik eller fönster >>Structural evolution and magnetic properties of underfluorinated C2F
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2012 (Engelska)Ingår i: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, nr 1, s. 79-83Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A series of layered inclusion compounds based on fluorinated graphite C2F x (x≤1) was obtained by a room temperature synthesis. Inclusion compounds (intercalates) of fluorinated graphite matrix were n-hexane and dichloromethane, i.e., organic guest molecules that differ in size and symmetry. The changes in C2F x stoichiometry are shown to have a decisive effect on magnetic properties of produced complexes. The spin concentration decreases with the increase of fluorine content in fluorocarbon matrix. All samples have groups of correlated spins; at the temperatures 1.75–5 K nonlinear magnetization is observed, indicating a high-spin state. Application of the Langevin formula shows that the clusters consist of 10–20 interacting spins.

Ort, förlag, år, upplaga, sidor
Springer, 2012
Nyckelord
Graphite fluoride, Magnetic properties, X-ray diffraction, Infrared spectroscopy
Nationell ämneskategori
Fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:umu:diva-45911 (URN)10.1007/s10948-011-1209-2 (DOI)
Tillgänglig från: 2011-08-20 Skapad: 2011-08-20 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
7. The influence of boron doping on magnetic properties of oxygen-eroded graphite
Öppna denna publikation i ny flik eller fönster >>The influence of boron doping on magnetic properties of oxygen-eroded graphite
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

A series of nanoporous oxygen-eroded graphites prepared by a redox reaction in a closed system between graphite and CuO, with varying amounts of boron, has been studied. We have found that introduction of boron affects the defect-induced magnetism of disordered nanoporous carbon in a complex way, changing both paramagnetic and diamagnetic contributions. Small concentrations of boron dopant enhance magnetic response from the system, while higher concentrations suppress magnetism due to annihilation of localized states.

Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:umu:diva-53567 (URN)
Tillgänglig från: 2012-04-02 Skapad: 2012-04-02 Senast uppdaterad: 2012-04-03

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