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145 results on '"Brueckel, Th."'

70. Strong coupling of Sm and Fe magnetism in SmFeAsO

Author

Nandi, S., Su, Y., Xiao, Y., Price, S., Wang, X. F., Chen, X. H., Herrero-Martin, J., Mazzoli, C., Walker, H. C., Paolasini, L., Francoual, S., Shukla, D. K., Strempfer, J., Chatterji, T., Kumar, C. M. N., Mittal, R., Roennow, H. M., Ruegg, Ch., McMorrow, D. F., and Brueckel, Th.

Published
2012

71. Effect of substitution of Y on the structural, magnetic, and thermal properties of hexagonal DyMnO3 single crystals

Author

Nair, Harikrishnan S, Kumar, CMN, Bhat, HL, Elizabeth, Suja, and Brueckel, Th

Subjects
Physics, Condensed Matter::Strongly Correlated Electrons, ddc:530
Abstract

We investigate the structural, magnetic, and specific heat behavior of the hexagonal manganite Dy0.5Y0.5MnO3 in order to understand the effect of dilution of Dy magnetism with nonmagnetic yttrium. In this compound, the triangular Mn lattice orders antiferromagnetic at T-N(Mn) approximate to 68 K observed experimentally in the derivative of magnetic susceptibility as well as in specific heat. In addition, a low-temperature peak at T-N(Dy) similar to 3 K is observed in specific heat which is attributed to rare earth order. The T-N(Mn) increases by 9 K compared to that of hexagonal (h) DyMnO3 while T-N(Dy) is unchanged. A change in slope of thermal evolution of lattice parameters is observed to occur at temperature close to T-N(Mn). This hints at strong magnetoelastic coupling in this geometric multiferroic. In magnetization measurements, steplike features are observed when the magnetic field is applied along the c axis which shift to higher fields with temperature and vanish completely above 40 K. The presence of different magnetic phases at low temperature and strong magnetoelastic effects can lead to such field-induced transitions which resemble metamagnetic transitions. This indicates the possibility of strong field-induced effects in dielectric properties of this material, which is unexplored to date.

Published
2011
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73. Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

Author

Disch, S., Hermann, R. P., Wetterskog, Erik, Podlesnyak, A. A., An, K., Hyeon, T., Salazar-Alvarez, German, Bergström, Lennart, Brueckel, Th., Disch, S., Hermann, R. P., Wetterskog, Erik, Podlesnyak, A. A., An, K., Hyeon, T., Salazar-Alvarez, German, Bergström, Lennart, and Brueckel, Th.

Abstract

We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Lande factor g = 2.05(2) as expected for maghemite (gamma-Fe2O3) nanoparticles. A large effective anisotropy field of B-A,B-eff = 0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles., AuthorCount:9

Published
2014
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74. Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

Author

Disch, Sabrina, Hermann, R. P., Wetterskog, E., Podlesnyak, A. A., An, K., Hyeon, T., Salazar-Alvarez, G., Bergstrom, L., Brueckel, Th., Disch, Sabrina, Hermann, R. P., Wetterskog, E., Podlesnyak, A. A., An, K., Hyeon, T., Salazar-Alvarez, G., Bergstrom, L., and Brueckel, Th.

Abstract

We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Lande factor g = 2.05(2) as expected for maghemite (gamma-Fe2O3) nanoparticles. A large effective anisotropy field of B-A,B-eff = 0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles.

Published
2014

77. Pressure-driven Phase Transition in CaFeAsF at 40 and 300 K

Author

Mishra, S K, primary, Mittal, R, additional, Chaplot, S L, additional, Ovsyannikov, S V, additional, Trots, D M, additional, Dubrovinsky, L, additional, Su, Y, additional, Brueckel, Th, additional, Matsuishi, S, additional, Hosono, H, additional, and Garbarino, G, additional

Published
2012
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80. High-Pressure Structural Phase Transitions in FeAs Based Compounds at Ambient and Low Temperatures

Author

Mittal, R., primary, Mishra, S. K., additional, Chaplot, S. L., additional, Ovsyannikov, S. V., additional, Greenberg, E., additional, Trots, D. M., additional, Dubrovinsky, L., additional, Su, Y., additional, Brueckel, Th., additional, Matsuishi, S., additional, Hosono, H., additional, Garbarino, G., additional, Garg, Alka B., additional, Mittal, R., additional, and Mukhopadhyay, R., additional

Published
2011
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83. Field-induced spin reorientation and giant spin-lattice coupling inEuFe2As2

Author

Xiao, Y., primary, Su, Y., additional, Schmidt, W., additional, Schmalzl, K., additional, Kumar, C. M. N., additional, Price, S., additional, Chatterji, T., additional, Mittal, R., additional, Chang, L. J., additional, Nandi, S., additional, Kumar, N., additional, Dhar, S. K., additional, Thamizhavel, A., additional, and Brueckel, Th., additional

Published
2010
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84. Pressure dependence of phonon modes across the tetragonal to collapsed-tetragonal phase transition inCaFe2As2

Author

Mittal, R., primary, Heid, R., additional, Bosak, A., additional, Forrest, T. R., additional, Chaplot, S. L., additional, Lamago, D., additional, Reznik, D., additional, Bohnen, K.-P., additional, Su, Y., additional, Kumar, N., additional, Dhar, S. K., additional, Thamizhavel, A., additional, Rüegg, Ch., additional, Krisch, M., additional, McMorrow, D. F., additional, Brueckel, Th., additional, and Pintschovius, L., additional

Published
2010
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86. Tetragonal To Collapsed Tetragonal Phase Transition In BaFe[sub 2]As[sub 2] and CaFe[sub 2]As[sub 2]

Author

Mittal, R., primary, Mishra, S. K., additional, Chaplot, S. L., additional, Ovsyannikov, S. V., additional, Greenberg, E., additional, Trots, D. M., additional, Dubrovinsky, L., additional, Su, Y., additional, Brueckel, Th., additional, Matsuishi, S., additional, Hosono, H., additional, Garbarino, G., additional, Aswal, Dinesh K., additional, and Debnath, Anil K., additional

Published
2010
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90. Phonon spectra inCaFe2As2andCa0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison withab initioand shell model calculations

Author

Mittal, R., primary, Rols, S., additional, Zbiri, M., additional, Su, Y., additional, Schober, H., additional, Chaplot, S. L., additional, Johnson, M., additional, Tegel, M., additional, Chatterji, T., additional, Matsuishi, S., additional, Hosono, H., additional, Johrendt, D., additional, and Brueckel, Th., additional

Published
2009
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97. Tetragonal To Collapsed Tetragonal Phase Transition In BaFe2As2 and CaFe2As2.

Author

Mittal, R., Mishra, S. K., Chaplot, S. L., Ovsyannikov, S. V., Greenberg, E., Trots, D. M., Dubrovinsky, L., Su, Y., Brueckel, Th., Matsuishi, S., Hosono, H., and Garbarino, G.

Subjects
PHASE transitions, BARIUM compounds, CALCIUM compounds, SUPERCONDUCTIVITY, PRESSURE, X-ray diffraction, EQUATIONS of state
Abstract

Superconductivity in MFe2As2 (M = Ba, Ca) compounds appears either at a critical doping level at ambient pressure or in the parent compound itself by application of pressure above a critical value. We report high pressure powder x-ray diffractions studies for these compounds at 300 K up to about 56 GPa using membrane diamond anvil cells. The measurements for BaFe2As2 show a new tetragonal to collapsed tetragonal phase transition at about 22 GPa that remains stable upto 56 GPa. CaFe2As2 is already known to transform to collapsed phase at 1.7 GPa at 300 K. Our measurements on CaFe2As2 do not show any post collapsed phase transition on increase of pressure 50 GPa at 300 K. It is important to note that the transition in both compounds occurs when they are compressed to almost the same value of the unit cell volume and attain similar ct/at ratios. We present a detailed analysis of the pressure dependence and structure phase transitions as well as equation of state in these important FeAs compounds that should be useful in the context of possible superconductivity in the collapsed phase. [ABSTRACT FROM AUTHOR]

Published
2010
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98. Amplitude, wavevector and frequency dependence of magnetic fluctuations in YBa2Cu3O6+δ

Author

Schaerpf, O., Capellmann, H., Brueckel, Th., Comberg, A., and Passing, H.

Abstract

Polarized neutrons and polarization analysis were used to determine the total amplitude of magnetic fluctuations in tetragonal YBa2Cu3O6+d for energies below 30 meV, both in the magnetically ordered state below and in the paramagnetic state above the Neél temperature. An energy analysis of the local magnetic correlation function (=S(r=0,?)) was performed. The wavevector dependence of the energy integrated correlation function at high temperatures is dominated by local (i.e.q-independent) fluctuations. Total intensity, energy and wavevector dependence are substantially different from those of stable moments with quasi two-dimensional couplings. Magnetic amplitude fluctuation might be responsible for the observed behaviour.

Published
1990
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99. Dynamical interaction of antiferromagnetic subsystems: a neutron scattering study of the spinwave spectrum of the garnet Fe2Ca3(GeO4)3

Author

Brueckel, Th., Dorner, B., Gukasov, A. G., Plakhty, V. P., Prandl, W., Shender, E. F., and Smirnow, O. P.

Abstract

The Fe3+ ions in the garnet Ca3Fe2Ge3O12 form two identical antiferromagnetic subsystems. The interaction between the two subsystems is vanishing within molecular field approximation forq=0. A coupling appears due to the spin fluctuations. The dynamics of the system is described by the Hamiltonian for a Heisenberg antiferromagnet. Symmetry requirements impose two exchange parameters between the sublattices (nearest neighbours)J1 in the direction of the 3-fold axis andJ'1 in the other three space diagonals. The interaction within each sublattice (second nearest neighbours) is described by the exchange parameterJ2. The measured spin wave dispersion curves for the three principal symmetry directions are very well reproduced by a model calculation withJ1=-0.909(9) K,J'1=-0.307(8) K andJ2=-0.615(2)K. The observed intensities are in agreement with predictions from the model. Forq?0 the model predicts two acoustic branches going towards zero frequency. A calculation beyond linear spin wave theory forq=0 predicts a quantum gap for the lower acoustic branch. This gap has been found at 0.033(4) THz. An anisotropy gap of 0.007 THz has been taken from the literature.

Published
1988
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100. Anomalous Hall effect and magnetic structure of the topological semimetal (Mn0.78Fe0.22)3Ge

Author

Rai, V., Stunault, A., Schmidt, W., Jana, S., Persson, J., Soh, J. -R., Brueckel, Th., and Nandi, S.

Subjects
mn3sn, weak ferromagnetism, transition, triangular spin configuration
Abstract

Me3+8Ge, being a Weyl semimetal, shows a large anomalous Hall effect (AHE), which decreases slowly with an increase in 8 from 0.1 to 0.4. However, AHE in this compound remains significantly large in the whole range of 8 because of the robust nature of the topology of bands. To explore the possibility of tuning the anomalous transport effects in Weyl semimetals, we have studied the single-crystal hexagonal-(Mn0.78Fe0.22)3Ge compound. Magnetization of this compound shows two magnetic transitions at 242 K (TN1) and 120 K (TN2). We observed that the AHE persists between TN2-TN1 and vanishes below TN2. Further, we performed single-crystal neutron diffraction experiments (using spherical neutron polarimetry and unpolarized neutron diffraction) to determine the magnetic structures of (Mn0.78Fe0.22)3Ge at different temperatures. Our neutron diffraction results show that the sample possesses a collinear antiferromagnetic structure below TN2. However, the magnetic structure of the sample remains noncollinear antiferromagnetic, the same as Mn3Ge, between TN1 to TN2. The presence of AHE, and noncollinear magnetic structure in (Mn0.78Fe0.22)3Ge, between TN1 and TN2, suggest the existence of Weyl points in this temperature regime. Below TN2, AHE is absent, and the magnetic structure also changes to a collinear antiferromagnetic structure. These observations signify a strong link between the magnetic structure of the sample and AHE.

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