Ultra-broadband EPR spectroscopy in field and frequency domains

Neugebauer, Petr; Bloos, D.; Marx, Raphael; Lutz, Philipp; Kern, Michal; Aguilà, David; Vaverka, J.; Laguta, Oleksii; Dietrich, Carolin; Clérac, Rodolphe; Slageren, Joris van

doi:10.1039/c7cp07443c

Cited by 60 publications

(53 citation statements)

References 58 publications

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“…Additional EPR measurements were performed with the home-made high frequency spectrometer operated at frequencies from 82.5 GHz up to 1100 GHz in the magnetic field 0  15 T and the temperature 4.6 and 260 K. The field sweep resolution was 28000 points for the 0 15 T region with the sweep time of 100-150 min for one spectrum. Details of this spectrometer design can be found in [31] and in supplementary material to this publication.…”

Section: Methodsmentioning

confidence: 99%

Oxygen-vacancy donor-electron center in Y3Al5O12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

et al. 2020

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F + center, an electron trapped at oxygen vacancy (VO), was investigated in the oxygen deficient Y3Al5O12 (YAG) garnet crystals by electron paramagnetic resonance (EPR). The measurements were performed in the wide temperature interval 5450 K and the frequency region 9.4350 GHz with using both the conventional continue wave and pulse EPR technique. The pulse electron-nuclear double resonance was applied to resolve the hyperfine interaction of the trapped electron with surrounding nuclei. The measurements show that at low temperatures, T < 50 K, EPR spectrum of the F + center is anisotropic with g factors in the range 1.9991.988 and originates from three magnetically inequivalent positions of the center in garnet lattice according to different directions of the Al(IV) -VO -Al(VI) chains, where Al(IV) and Al(VI) are the tetrahedral and octahedral Al sites, respectively. As the temperature increases, the EPR spectrum becomes isotropic suggesting a motional averaging of the anisotropy due to motion of F + -center electron between neighboring oxygen vacancies. With further increase of the temperature to T > 200 K, we observed delocalization of the F + -center electron into the conduction band with the activation energy about 0.40.5 eV that resulted in substantial narrowing of the EPR spectral line with simultaneous change of its shape from the Gaussian to Lorentzian due to diminish up to zero of the Fermi contact hyperfine field at 27 Al and 89 Y nuclei. Such temperature behavior of the F + -center electron in YAG is completely similar to behavior of a donor electron in a semiconductor. Our findings is further supported by measurements of the conductivity and dielectric properties. In particular, these data show that the conduction electrons are not homogeneously distributed in the crystal: there are high-conductive regions separated by poorly-conductive dielectric layers. This leads to the so-called Maxwell-Wagner dielectric relaxation with huge apparent dielectric constant at low frequencies. To the best of our knowledge, this is probably the first observation of a donor-like behavior of F + center in wide band-gap insulating crystals.

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Section: Methodsmentioning

confidence: 99%

Oxygen-vacancy donor-electron center in Y3Al5O12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

et al. 2020

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“…High Field EPR : HFEPR measurements were obtained on ground powders (≈15 mg of sample each) wrapped in teflon and pressed into a 5 mm cylindrical pellet to avoid reorientation of the microcrystallites. The radiation source (0–20 GHz signal generator, Anritsu) was combined with an amplifier‐multiplier chain (VDI) to obtain the desired frequencies.…”

Section: Methodsmentioning

confidence: 99%

Magnetic Anisotropy Switch: Easy Axis to Easy Plane Conversion and Vice Versa

Perfetti

Sørensen

Hansen

et al. 2018

Adv Funct Materials

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The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single-molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic anisotropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic anisotropy switches as a function of these parameters. Thus, this paper experimentally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field.

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“…Additional EPR measurements were performed with the home-made high frequency spectrometer operated at frequencies from 82.5 GHz up to 1100 GHz in the magnetic field 0 − 15 T and temperatures 10 -300 K. The field sweep resolution was 28000 points for the 0− 15 T region with the sweep time of 100-150 min for one spectrum. Details of this spectrometer design can be found in [28] and in supplementary material to this publication. Five bands with maxima at about 424 nm (1), 598 nm (2), 822 nm (3), 1150 nm (4) and 1300 nm (5) can be clearly resolved in the spectra.…”

Section: Samples and Experimental Setupmentioning

confidence: 99%

Vanadium in yttrium aluminum garnet: Charge states and localization in the lattice

et al. 2019

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Vanadium ions charge states and their incorporation in the yttrium aluminum garnet Y 3 Al 5 O 12 (YAG) lattice were studied by the correlated optical absorption and electron paramagnetic resonance (EPR) measurements. In as-grown crystals, the occupation of the V 3+ at both the octahedral and tetrahedral aluminum sites was proven. The V 3+ to V 4+ charge transformation was observed after annealing in air, whereas annealing in the hydrogen atmosphere resulted exclusively in a slight weakening of the V 3+ absorption bands due to partial recharge of these ions. Spin Hamiltonian parameters of the V 3+ and V 4+ ions at the tetrahedral sites including the zero field splitting and the 51 V hyperfine constants have been determined using the high-frequency, up to 300 GHz, EPR measurements. From the analysis of the spin Hamiltonian parameters in the framework of the crystal field theory, the ground state energy levels splitting of the V 3+ and V 4+ ions were calculated. The charge distribution over the tetrahedral V 3+ and its nearest oxygen surroundings was found to be strongly inhomogeneous whereas the tetrahedral V 4+ ion concentrated the charge with very weak participation of surrounding ligands. Furthermore, the correlation of the optical and EPR data allowed the proper assignment of the optical absorption peaks in YAG:V crystals.

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Ultra-broadband EPR spectroscopy in field and frequency domains

Cited by 60 publications

References 58 publications

Oxygen-vacancy donor-electron center in Y3Al5O12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

Oxygen-vacancy donor-electron center in Y3Al5O12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

Magnetic Anisotropy Switch: Easy Axis to Easy Plane Conversion and Vice Versa

Vanadium in yttrium aluminum garnet: Charge states and localization in the lattice

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