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Longitudinal Magnetic Field (longitudinal + magnetic_field)

Distribution by Scientific Domains

Physics and Astronomy	100%

Distribution within Physics and Astronomy

Astronomy & Astrophysics	63%
Solid State Physics	18%

Selected Abstracts

Photon echo in ruby doped only by 53Cr isotope ions

LASER PHYSICS LETTERS, Issue 8 2008
V.V. Samartsev
Abstract The signals of photon echo (PE) are investigated firstly in a ruby crystal doped only by the 53Cr isotope ions in a concentration of 0.03 , 0,05 wt%. The optical experiments were performed in backward regime at the wavelength of 693.4 nm both with a low magnetic field (200 G) and without it. Since the 53Cr isotope ions have hyperfine structure of levels the special attention was paid to the study of the stimulated photon echo and primarily to the investigation of its decay kinetics. It is established that this decay has a form which is typical to the signals of longlived PE. But in contrast to the long-lived PE the decay time in our case is less than the lifetime of the excited 2E () state. The signals of primary photon echo and stimulated photon echo at a low longitudinal magnetic field and their decay curves are investigated. We observed the beats of temporal shape of these signals with a period of several tens of nanoseconds. Theoretical analysis shows that they are due to the hyperfine interaction of valence electrons of 53Cr isotope ions with their own nuclei. The obtained decay curves allow us to estimate the phase relaxation time at the presence of a magnetic field. It proves to be equal to 98 ns. The spectrum of stimulated photon echo signal in the doped ruby exposed to a magnetic field is measured. (© 2008 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Laser frequency stabilization using selective reflection from a vapor cell with a half-wavelength thickness

LASER PHYSICS LETTERS, Issue 11 2007
E.A. Gazazyan
Abstract We have experimentally studied the selective reflection spectra of a circularly-polarized laser beam from a sub-micrometric Rb vapor cell with a thickness L around , /2 (, = 780 nm being the laser wavelength tuned to the D2 line) in the presence of a longitudinal magnetic field. Based on the results of these studies, we propose a new method for the tunable locking of the diode laser frequency, which does not require frequency modulation nor complex electronics. The experimental realization of the technique has demonstrated its effectiveness and its competitiveness with the known DAVVL-type methods. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Discovery of magnetic fields in the , Cephei star ,1 CMa and in several slowly pulsating B stars,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006
S. Hubrig
ABSTRACT We present the results of a magnetic survey of a sample of eight , Cephei stars and 26 slowly pulsating B (SPBs) stars with the FOcal Reducer low dispersion Spectrograph at the Very Large Telescope. A weak mean longitudinal magnetic field of the order of a few hundred Gauss is detected in the , Cephei star ,1 CMa and in 13 SPB stars. The star ,1 CMa becomes the third magnetic star among the , Cephei stars. Before our study, the star , Cas was the only known magnetic SPB star. All magnetic SPB stars for which we gathered several magnetic field measurements show a field that varies in time. We do not find a relation between the evolution of the magnetic field with stellar age in our small sample. Our observations imply that , Cephei and SPB stars can no longer be considered as classes of non-magnetic pulsators, but the effect of the fields on the oscillation properties remains to be studied. [source]

Spin orientation of excitons, trions and tetraons in charge tunable InP quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009
Yasuaki Masumoto
Abstract In the longitudinal magnetic field, photoluminescence (PL) polarization in InP quantum dots (QDs) dramatically changed depending on the number of doped electrons. Under linearly polarized excitation, PL polarizes resonantly at two magnetic fields where bright and dark excitons anticross each other in neutral QDs. On the other hand, PL polarization monotonously increases with the increase of longitudinal magnetic field in one- and two-electron doped QDs, where thermal spin orientation of a photoexcited hole determines the PL polarization of a trion and a tetraon. At low temperatures, however, the electron-hole exchange interaction reduces the thermal spin orientation of holes. In two-electron doped QDs, the anisotropic electron-hole exchange interaction gives small structure in the magnetic-field-dependent circular polarization at the low field region. Time-resolved circular polarization clearly shows the dynamical spin polarization process in charged QDs in the longitudinal magnetic field. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Measurements of mean longitudinal magnetic fields in the Of?p stars HD 108 and HD 191612,

ASTRONOMISCHE NACHRICHTEN, Issue 8 2010
S. Hubrig
Abstract Using polarimetric spectra obtained with the SOFIN spectrograph installed at the Nordic Optical Telescope, we detect a longitudinal magnetic field ,Bz, = ,168±35 G in the Of?p star HD 108. This result is in agreement with the longitudinal magnetic field measurement of the order of ,150 G recently reported by the MiMeS team. The measurement of the longitudinal magnetic field in the Of?p star HD 191612 results in ,Bz, = +450±153 G. The only previously published magnetic field measurement for this star showed a negative longitudinal magnetic field ,Bz, = ,220±38 G, indicating a change of polarity over ,100 days. Further, we report the detection of distinct Zeeman features in the narrow Ca II and Na I doublet lines for both Of?p stars, hinting at the possible presence of material around these stars. The origin of these features is not yet clear and more work is needed to investigate how magnetic fields interact with stellar wind dynamics (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

New magnetic field measurements of , Cephei stars and slowly pulsating B stars,

ASTRONOMISCHE NACHRICHTEN, Issue 4 2009
S. Hubrig
Abstract We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate , Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B-type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three , Cephei stars and two stars suspected to be , Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3, has been diagnosed in two normal B-type stars, the nitrogen-rich early B-type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of , Cephei stars have detected magnetic fields: Out of 13 , Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected , Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non-magnetic pulsating stars in the H-R diagram. We find that their domains in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i -values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dependence of the permeability-frequency spectra of Fe88Zr7B4Cu alloys on dc magnetic fields

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2004
W. Qin
Abstract Effects of applied dc transverse and longitudinal magnetic fields on the dynamic magnetization of Nanoperm alloys are studied by using permeability spectroscopy. It is observed that the permeability-frequency spectra of Nanoperm alloys are very sensitive to the dc transverse magnetic fields. The applied dc transverse magnetic fields may strengthen the domain wall pinning, making the permeability decrease and the relaxation frequency move toward higher frequency. The dc longitudinal magnetic fields have no significant influence on the permeability-frequency spectra. The contribution to initial permeability only results from the bulging of the domain walls parallel to the applied ac magnetic field. The effect of the Earth's magnetic field on the dynamic magnetic properties of Nanoperm alloys must be considered in actual application. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Measurements of mean longitudinal magnetic fields in the Of?p stars HD 108 and HD 191612,

Evolution of magnetic fields in stars across the upper main sequence: II.

ASTRONOMISCHE NACHRICHTEN, Issue 6 2007
Observed distribution of the magnetic field geometry
Abstract We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M, are concentrated towards the centre of the main-sequence band. In contrast, stars with masses M > 3 M, seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M, and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main-sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities , is detected in both higher and lower mass stars. It is quite possible that the angle , becomes close to 0. in slower rotating stars of mass M > 3 M, too, analog to the behaviour of angles , in slowly rotating stars of M < 3 M,. The obliquity angle distribution as inferred from the distribution of r -values appears random at the time magnetic stars become observable on the H-R diagram. After quite a short time spent on the main sequence, the obliquity angle , tends to reach values close to either 90. or 0. for M < 3 M,. The evolution of the obliquity angle , seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of , with the elapsed time on the main sequence for stars with M > 3 M,, no similar trend is found for stars with M < 3 M,. However, the predominance of high values of , at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]