208 research outputs found
Magnetoelectric properties of [FeCl(HO)] with K, Rb, Cs
The compounds [FeCl(HO)] with K, Rb, Cs are identified as
new linear magnetoelectric materials. We present a detailed investigation of
their linear magnetoelectric properties by measurements of pyroelectric
currents, dielectric constants and magnetization. The anisotropy of the linear
magnetoelectric effect of the K-based and Rb-based compound is consistent with
the magnetic point group , already reported in literature. A symmetry
analysis of the magnetoelectric effect of the Cs-based compound allows to
determine the magnetic point group and to develop a model for its
magnetic structure. In addition, magnetic-field versus temperature phase
diagrams are derived and compared to the closely related multiferroic
(NH)[FeCl(HO)].Comment: 17 pages, 10 figures (updated to the weakly revised version that has
been accepted for publication
Anisotropy study of multiferroicity in the pyroxene NaFeGeO
We present a study of the anisotropy of the dielectric, magnetic and
magnetoelastic properties of the multiferroic clinopyroxene NaFeGeO.
Pyroelectric currents, dielectric constants and magnetic susceptibilities as
well as the thermal expansion and the magnetostriction were examined on large
synthetic single crystals of NaFeGeO. The spontaneous electric
polarization detected below K in an
antiferromagnetically ordered state ( K) is mainly lying
within the plane with a small component along , indicating a triclinic
symmetry of the multiferroic phase of NaFeGeO. The electric
polarization can be strongly modified by applying magnetic fields along
different directions. We derive detailed magnetic-field versus temperature
phase diagrams and identify three multiferroic low-temperature phases, which
are separated by a non-ferroelectric, antiferromagnetically ordered state from
the paramagnetic high-temperature phase.Comment: 14 pages, 8 figures. (minor modifications and corrections of the
text
Kinetics of the Multiferroic Switching in MnWO
The time dependence of switching multiferroic domains in MnWO has been
studied by time-resolved polarized neutron diffraction. Inverting an external
electric field inverts the chiral magnetic component within rise times ranging
between a few and some tens of milliseconds in perfect agreement with
macroscopic techniques. There is no evidence for any faster process in the
inversion of the chiral magnetic structure. The time dependence is well
described by a temperature-dependent rise time suggesting a well-defined
process of domain reversion. As expected, the rise times decrease when heating
towards the upper boundary of the ferroelectric phase. However, switching also
becomes faster upon cooling towards the lower boundary, which is associated
with a first-order phase transition
Muon-spin relaxation and heat capacity measurements on the magnetoelectric and multiferroic pyroxenes LiFeSi2O6 and NaFeSi2O6
The results of muon-spin relaxation and heat capacity measurements on two
pyroxene compounds LiFeSi2O6 and NaFeSi2O6 demonstrate that despite their
underlying structural similarity the magnetic ordering is considerably
different. In LiFeSi2O6 a single muon precession frequency is observed below
TN, consistent with a single peak at TN in the heat capacity and a commensurate
magnetic structure. In applied magnetic fields the heat capacity peak splits in
two. In contrast, for natural NaFeSi2O6, where multiferroicity has been
observed in zero-magnetic-field, a rapid Gaussian depolarization is observed
showing that the magnetic structure is more complex. Synthetic NaFeSi2O6 shows
a single muon precession frequency but with a far larger damping rate than in
the lithium compound. Heat capacity measurements reproduce the phase diagrams
previously derived from other techniques and demonstrate that the magnetic
entropy is mostly associated with the build up of correlations in the
quasi-one-dimensional Fe3+ chains
Low-temperature ordered phases of the spin- XXZ chain system CsCoCl
In this study the magnetic order of the spin-1/2 XXZ chain system
CsCoCl in a temperature range from 50 mK to 0.5 K and in applied
magnetic fields up to 3.5 T is investigated by high-resolution measurements of
the thermal expansion and the specific heat. Applying magnetic fields along a
or c suppresses completely at about 2.1 T. In addition, we find
an adjacent intermediate phase before the magnetization saturates close to 2.5
T. For magnetic fields applied along b, a surprisingly rich phase diagram
arises. Two additional transitions are observed at critical fields T and T, which we propose to
arise from a two-stage spin-flop transition.Comment: 10 pages, 10 figure
Electronic excitations in J=0 Os halides studied by RIXS and optical spectroscopy
We demonstrate that the cubic antifluorite-type halides KOsCl,
KOsBr, and RbOsBr are excellent realizations of non-magnetic
J=0 compounds. The magnetic susceptibility shows the corresponding Van-Vleck
type behavior and no sign of defects. We investigate the electronic excitations
with two complementary techniques, resonant inelastic x-ray scattering (RIXS)
and optical spectroscopy. This powerful combination allows us to thoroughly
study, e.g., on-site intra- excitations and -to-
excitations as well as inter-site excitations across the Mott gap and an
exciton below the gap. In this way, we determine the electronic parameters with
high accuracy, altogether yielding a comprehensive picture. In KOsCl,
we find the spin-orbit coupling constant =0.34 eV, Hund's coupling
=0.43 eV, the onset of excitations across the Mott gap at =2.2 eV,
the cubic crystal-field splitting 10Dq=3.3 eV, and the charge-transfer energy
=4.6 eV. With =1.3, KOsCl is in the
intermediate-coupling regime. In a -only Kanamori picture, the above
values correspond to =0.41 eV and =0.28 eV, which is
very close to results reported for related iridates. In the tetragonal
phase at 5 K, the non-cubic crystal field causes a peak splitting of the J=1
state as small as 4 meV. Compared to KOsCl, the bromides KOsBr
and RbOsBr show about 12-14 % smaller values of 10Dq and ,
while the spin-orbit-entangled intra- excitations below 2 eV and hence
and are reduced by less than 4 %. Furthermore, the Mott gap in
KOsBr is reduced to about 1.8 eV.Comment: 14 pages, 14 figure
Annual Feedback Is an Effective Tool for a Sustained Increase in Calcium Intake among Older Women
We aimed to optimize calcium intake among the 2,000+ older women taking part in the Vital D study. Calcium supplementation was not included in the study protocol. Our hypothesis was that annual feedback of calcium intake and informing women of strategies to improve calcium intake can lead to a sustained increase in the proportion of women who consume adequate levels of the mineral. Calcium intake was assessed on an annual basis using a validated short food frequency questionnaire (FFQ). Supplemental calcium intake was added to the dietary estimate. Participants and their nominated doctor were sent a letter that the participant’s estimated daily calcium intake was adequate or inadequate based on a cutoff threshold of 800 mg/day. General brief statements outlining the importance of an adequate calcium intake and bone health were included in all letters. At baseline, the median daily consumption of calcium was 980 mg/day and 67 percent of 1,951 participants had calcium intake of at least 800 mg per day. Of the 644 older women advised of an inadequate calcium intake at baseline (<800 mg/day), 386 (60%) had increased their intake by at least 100 mg/day when re-assessed twelve months later. This desirable change was sustained at 24 months after baseline with almost half of these women (303/644) consuming over 800 mg calcium per day. This study devised an efficient method to provide feedback on calcium intake to over 2,000 older women. The improvements were modest but significant and most apparent in those with a low intake at baseline. The decreased proportion of these women with an inadequate intake of calcium 12- and 24-months later, suggests this might be a practical, low cost strategy to maintain an adequate calcium intake among older women
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