290 research outputs found
Modes of magnetic resonance of S=1 dimer chain compound NTENP
The spin dynamics of a quasi one dimensional bond alternating spin-gap
antiferromagnet Ni(CHN)NO(ClO) (abbreviated as NTENP) is
studied by means of electron spin resonance (ESR) technique. Five modes of ESR
transitions are observed and identified: transitions between singlet ground
state and excited triplet states, three modes of transitions between spin
sublevels of collective triplet states and antiferromagnetic resonance
absorption in the field-induced antiferromagnetically ordered phase.
Singlet-triplet and intra-triplet modes demonstrate a doublet structure which
is due to two maxima in the density of magnon states in the low-frequency
range. A joint analysis of the observed spectra and other experimental results
allows to test the applicability of the fermionic and bosonic models. We
conclude that the fermionic approach is more appropriate for the particular
case of NTENP.Comment: 11 pages, 11 figures, published in Phys.Rev.
Electron spin resonance study of anisotropic interactions in a two-dimensional spin gap magnet PHCC
Fine details of the excitation spectrum of the two-dimensional spin-gap
magnet PHCC are revealed by electron spin resonance investigations. The values
of anisotropy parameters and the orientations of the anisotropy axes are
determined by accurate measurements of the angular, frequency-field and
temperature dependences of the resonance absorption. The properties of a
spin-gap magnet in the vicinity of critical field are discussed in terms of
sublevel splittings and g-factor anisotropy.Comment: submitted to PR
Finite amplitudes helical waves on the surface of the conducting fluid earth core as an example of the self-exciting homopolar heterogeneous dynamo
International audienceHelical waves of the finite amplitude on a surface of the fluid conducting Earth core are examined for generation of the magnetic field. Estimates are made for the differentially rotating cylindrical conducting fluid body, with the helical surface wave structure on its top. This structure is similar to the self-exciting Faraday-disk homopolar heterogeneous dynamo. Estimations of angular velocity and magnetic field magnitude for a polar vortex on the surface of the Earth's liquid outer core gives reasonable numbers and proves this hypothesis to be of value for further detailed analysis. As magnetic field generation by the helical structure is a surface effect, it is possible to find connection between Earth magnetic field fluctuations and fast relief changes on the iron fluid core ? the silicate mantle boundary of the Earth
Novel magnetic phases in a Gd2Ti2O7 pyrochlore for a field applied along the [100] axis
We report on longitudinal and transverse magnetisation measurements performed
on single crystal samples of Gd2Ti2O7 for a magnetic field applied along the
[100] direction. The measurements reveal the presence of previously unreported
phases in fields below 10 kOe in an addition to the higher-field-induced phases
that are also seen for H//[111], [110], and [112]. The proposed H-T phase
diagram for the [100] direction looks distinctly different from all the other
directions studied previously.Comment: 4 pages, 5 figure
Bose-Einstein condensation of magnons in TlCuCl
A quantitative study of the field-induced magnetic ordering in TlCuCl in
terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is
shown that the hitherto proposed simple BEC scenario is in quantitative and
qualitative disagreement with experiment. It is further shown that even very
small Dzyaloshinsky-Moriya interactions or a staggered tensor component of
a certain type can change the BEC picture qualitatively. Such terms lead to a
nonzero condensate density for all temperatures and a gapped quasiparticle
spectrum. Including this type of interaction allows us to obtain good agreement
with experimental data.Comment: 2 pages, 2 figures, submitted to SCES'0
Spin-resonance modes of the spin-gap magnet TlCuCl_3
Three kinds of magnetic resonance signals were detected in crystals of the
spin-gap magnet TlCuCl_3.
First, we have observed the microwave absorption due to the excitation of the
transitions between the singlet ground state and the excited triplet states.
This mode has the linear frequency-field dependence corresponding to the
previously known value of the zero-field spin-gap of 156 GHz and to the closing
of spin-gap at the magnetic field H_c of about 50 kOe.
Second, the thermally activated resonance absorption due to the transitions
between the spin sublevels of the triplet excitations was found. These
sublevels are split by the crystal field and external magnetic field.
Finally, we have observed antiferromagnetic resonance absorption in the
field-induced antiferromagnetic phase above the critical field H_c. This
resonance frequency is strongly anisotropic with respect to the direction of
the magnetic field.Comment: v.2: typo correction (one of the field directions was misprinted in
the v.1
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