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1
Content available remote

Hyperfine Fields and Lattice Deformations in Ba and Sr Hexaferrites

100%
Chlan V., Kouřil K., Štěpánková H.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
594-596
EN
Hyperfine magnetic fields on ⁵⁷Fe nuclei in Sr and Ba hexagonal ferrites are calculated in dependence on unit cell volume and c/a ratio. By analysing the local deformations of Fe-O-Fe triads the results are explained as changes to contact hyperfine field due to Fe-O covalency effects and supertransferred hyperfine fields. Most pronounced effect is found for bipyramidal iron Fe(b) where the total contact field is reduced due to noticeable shortening of Fe(b)-O bonds.
2
Content available remote

Giant Magnetoelectricity in Aluminium Substituted Y-Hexaferrites

100%
Novák P., Chlan V., Knížek K.
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issue 5
723-724
EN
The electron structure of Al containing Y-hexaferrite that exhibits the giant magnetoelectricity is calculated. Results show strong preference of Al for octahedral sites. Orbital moment of some of the iron ions is found to be unusually large.
3
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Study of Y-type Hexaferrite by Means of ^{57}Fe NMR and Electronic Structure Calculations

88%
Chlan V., Kouřil K., Štěpánková H., Řezníček R., Englich J.
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vol. 126
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issue 1
42-43
EN
The electron structure and site preferences of Zn and Fe cations in Y hexaferrite system were calculated. The hyperfine magnetic fields on ^{57}Fe nuclei were determined using WIEN2k and corrections for hyperfine contact interaction. The calculated fields were compared to ^{57}Fe nuclear magnetic resonance (NMR) experiment in Ba_2Zn_2Fe_{12}O_{22} single crystal with an aim of interpretation of experimental NMR spectrum.
4
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Antisite Defects in Epitaxial Films of Lutetium Doped Yttrium Iron Garnets Studied by Nuclear Magnetic Resonance

76%
Chlan V., Štěpánková H., Englich J., Řezníček R., Kouřil K., Kučera M., Nitsch K.
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issue 5
846-847
EN
Series of lutetium doped yttrium iron garnet films is studied by means of ^{57}Fe nuclear magnetic resonance. Satellite spectral lines are resolved and identified in the spectra and concentrations of lutetium in dodecahedral sites as well as yttrium/lutetium antisite defects in octahedral sites are estimated. Compared to yttrium, lutetium cations are found to have stronger disposition towards creating the antisite defects.
5
Content available remote

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

76%
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.
6
Content available remote

NMR Study of Multiferroic Iron Niobate Perovskites

76%
Kouřil K., Chlan V., Štěpánková H., Řezníček R., Laguta V., Raevski I.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
234-236
EN
We present ^{93}Nb, ^{207}Pb and ^{135,137}Ba NMR study of multiferroic lead iron niobate and barium iron niobate ceramics. We ascribe development of NMR spectra on cooling below room temperature to magnetism of ferric ions close to resonating nuclei and introduce a framework capable of describing key features of the observed temperature induced changes. We show that the ferric ions have much stronger influence on hyperfine fields at nuclei of large cations in lead compound and estimate strength of interaction of superantiferromagnetic clusters.
7
Content available remote

Tuned Probehead for NMR Spectroscopy in Magnetically Ordered Materials

64%
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.
8
Content available remote

Distribution of Zn in Magnetoelectric Y-Type Hexaferrite

64%
Kouřil K., Chlan V., Štěpánková H., Telfah A., Novák P., Knížek K., Hiraoka Y., Kimura T.
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issue 5
732-733
EN
We employ ^{67}Zn NMR to study distribution of Zn^{2+} in cationic sites of magnetoelectric Y-type hexaferrite single crystal, Ba_{0.5} Sr_{1.5} Zn_2 Fe_{12} O_{22}. The experimental data are interpreted by comparison with NMR spectra simulated from ab initio calculated hyperfine parameters.
9
Content available remote

Nuclear Magnetic Resonance in Hexaferrite/Maghemite Composite Nanoparticles

64%
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.
10
Content available remote

Cluster Superconductivity in the Magnetoelectric Pb(Fe_{1/2}Sb_{1/2})O₃ Ceramics

52%
Laguta V., Marysko M., Stephanovich V., Raevsky I., Olekhnovich N., Pushkarev A., Radyush Y., Raevskaya S., Kuzian R., Chlan V., Štěpánková H.
Acta Physica Polonica A
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2017
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vol. 131
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issue 6
1534-1539
EN
We report the observation of cluster (local) superconductivity in the magnetoelectric Pb(Fe_{1/2}Sb_{1/2})O₃ ceramics prepared at a hydrostatic pressure of 6 GPa and temperatures 1200-1800 K to stabilize the perovskite phase. The superconductivity is manifested by an abrupt drop of the magnetic susceptibility at the critical temperature T_{c} ≈7 K. Both the magnitude of this drop and T_{c} decrease with magnetic field increase. Similarly, the low-field paramagnetic absorption measured by EPR spectrometer drops significantly below T_{c} as well. The observed effects and their critical magnetic field dependence are interpreted as manifestation of the superconductivity and the Meissner effect in metallic Pb nanoclusters existing in the ceramics. Their volume fraction and average size were estimated as 0.1-0.2% and 140-150 nm, respectively. The superconductivity related effects disappear after oxidizing annealing of the ceramics.
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