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Structure of Iron Oxide Nanoparticles Studied by ^{57}Fe NMR

100%
Křišťan P., Chlan V., Štěpánková H., Řezníček R., Görnert P., Payer P.
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vol. 126
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issue 1
138-139
EN
In this work we apply nuclear magnetic resonance (NMR) spectroscopy of ^{57}Fe nuclei for investigation of submicron and nanocrystalline iron oxide systems. The studied iron oxide particles are obtained from ferrous hydroxide gels (prepared from FeCl_{2} and KOH) by aging at elevated temperatures (90 °C) with KNO_{3} as oxidant. The ^{57}Fe NMR spectra of the samples are measured in temperature range 4.2-370 K in a zero external magnetic field. Signals of ^{57}Fe nuclei assigned to tetrahedral and octahedral iron sites are well resolved. The NMR spectra and their temperature dependences are compared with those of stoichiometric and nonstoichiometric magnetite single crystals, as well as with samples of maghemite.
2
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Tuned Probehead for NMR Spectroscopy in Magnetically Ordered Materials

84%
Sedlák B., Kouřil K., Chlan V., Řezníček R., Křišťan P., Pfeffer M., Englich J., Štěpánková H.
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issue 5
924-925
EN
This work describes the design of a tuned NMR probehead that was developed for measurement of very broad spectra in fully impedance matched mode. The probehead is constructed as an insert of continuous flow cryostat to allow operation down to helium temperatures. Properties of the probehead are demonstrated on ^{57}Fe NMR in magnetic oxide with spinel structure.
3
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Nuclear Magnetic Resonance in Hexaferrite/Maghemite Composite Nanoparticles

84%
Křišťan P., Hondlík O., Štěpánková H., Chlan V., Kouřil K., Řezníček R., Pollert E., Veverka P.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
514-516
EN
Due to their bio-compatibility and non-toxicity, ferrimagnetic iron oxides are suitable for various medical applications. In the case of hyperthermia, the promising approach how to reach desired magnetic properties is to combine more phases into a composite material. A series of samples containing maghemite and M-hexaferrite was prepared by sol-gel method with subsequent thermal treatment where annealing temperature and time were varied. The samples were characterized by X-ray diffraction. In this paper we focused mainly on application of nuclear magnetic resonance spectroscopy to investigate these strongly inhomogeneous nanoparticle composites. Frequency-swept ⁵⁷Fe NMR spectra of nanoparticle samples were measured in a zero external magnetic field at 4.2 K. Utilizing differences in optimal excitation field strengths and in relaxation times, we were able to resolve NMR signal assigned to hexagonal ferrite of M-phase from signal which showed features attributed to maghemite.
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