arXiv subjects

D. Dimitrov

Publications and source records attributed to D. Dimitrov.

40 records · Page 3Linked to original sources

arXiv2007

Search for pulsation among suspected A-type binaries and the new multiperiodic Delta Scuti star HD217860

We have explored a sample of suspected A-type binaries in a systematic way, both spectroscopically and photometrically. Due to their location in the H-R diagram, indications of pulsation and/or chemical peculiarities among these suspected binary (or multiple) systems may be found. High-resolution spectroscopy obtained with the ELODIE and MUSICOS spectrographs was used in combination with a few nights of differential CCD photometry in order to search for pulsation(s). Of the 32 investigated targets, eight are spectroscopic binaries, one of which is a close binary also showing eclipses, and three have been identified as Delta Scuti pulsators with rapid line-profile variations. Among the latter stars, HD 217860 reveals interesting multiperiodic photometric and spectroscopic variations, with up to eight frequencies common to two large photometric data sets. We suggest that at least one radial overtone mode is excited among the two most dominant frequencies. We furthermore found evidence for a strong modulation of the amplitude(s) and/or the (radial) frequency content of this intriguing Delta Scuti star.

astro-ph↗

arXiv2007

Parameters of the Dzyaloshinsky-Moriya type weak ferromagnetism for some perovskite compounds

Compounds with distorted perovskite structure of the 4-f and 3-d transition metals with the common formula LnTO3 (where Ln is rare-earth element, T is an element from the Fe group) are the most multifold binary oxides of these two groups elements. Wide range of stability for this structure allows the realization of combinations of the Lanthanides with all the transition metals except the Nickel. Quite interesting physical phenomena take place in these oxides like charge and orbital ordering; relatively independent magnetic lattices of the both metals; particular magnetic structures; high optical indicators; giant magneto-resistance; peculiar dielectric and ferroelectric properties etc. We have investigated the magnetic properties of pure ferrites and chromium-based materials as well as of some mixed type oxides like HoxTb1-xO3, HoMnxFe1-xO3, HoMnxCr1-xO3 and DyFexCr1-xO3.

cond-mat.str-el↗

arXiv2007

Peculiarities in the properties of some rare-earth compounds with orthorhombic structures

Rare-earth manganites are fascinating, because they display a wide variety of fundamental properties from magnetism to ferroelectricity, from colossal magnetoresistance to semi-metallicity, and because they can be used in a number of important technological applications such as controlling a magnetic memory by an electric field or vice versa, new types of attenuators or transducers etc. In this paper, we present our investigation on monocrystal samples with an orthorhombic structure, grown in two different space groups: D2h(16) for La0.78Pb0.22MnO3 and Pr0.7Sr0.3MnO3 and D2h(9) for HoMn2O5 and TbMn2O5. The doped perovskite manganites Ln1-x Ax MnO3 (where Ln is a rare-earth ion and A is a divalent ion) from the group D2h(16), which crystallized in different modifications of the perovskite structure, characterized by the parameter deformation of the type c/√2<b<a. Many properties of these compounds (especially the giant magnetoresistance GMR, being interesting for practical applications) depend strongly on the carrier density, on the specific zone structure, on the type and the quantity of dopants, on the defects of the crystal and their magnetic structure, or on the applied magnetic fields.

cond-mat.other↗

arXiv2004

Magnetic properties and Hall effect of $Pr_{0.7}Sr_{0.3}MnO_3$ single crystal

Measurements of DC magnetization, AC susceptibility and Hall effect of $Pr_{0.7}Sr_{0.3}MnO_3$ single crystal are reported. The various features are discussed in terms of competing electronic and spin ordering phase transitions, in particular concerning the $e_g$ and $t_{2g}$ competition and its effect on spin ordering.

cond-mat.str-el↗