2,123 research outputs found
Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6
Exchange bias effect in the ferromagnetic double perovskite compound
YCoMnO, which is also a multiferroic, is reported. The exchange bias,
observed below 8~K, is explained as arising due to the interface effect between
the ferromagnetic and antiferromagnetic clusters created by {\it antisite}
disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with
metamagnetic "steps" and significant coercive field, 10~kOe are
observed in this compound which has a 75~K. A model based on
growth of ferromagnetic domains overcoming the elastic energy of structurally
pinned magnetic interfaces, which closely resembles martensitic-like
transitions, is adapted to explain the observed effects. The role of {\it
antisite} disorder in creating the domain structure leading to exchange bias
effect is highlighted in the present work.Comment: 4 pages two-column, 4 figures, accepted to Appl. Phys. Let
Anomalous temperature-induced volume contraction in GeTe
The recent surge of interest in phase change materials GeTe,
GeSbTe, and related compounds motivated us to revisit the
structural phase transition in GeTe in more details than was done before.
Rhombohedral-to-cubic ferroelectric phase transition in GeTe has been studied
by high resolution neutron powder diffraction on a spallation neutron source.
We determined the temperature dependence of the structural parameters in a wide
temperature range extending from 309 to 973 K. Results of our studies clearly
show an anomalous volume contraction of 0.6\% at the phase transition from the
rhombohedral to cubic phase. In order to better understand the phase transition
and the associated anomalous volume decrease in GeTe we have performed phonon
calculations based on the density functional theory. Results of the present
investigations are also discussed with respect to the experimental data
obtained for single crystals of GeTe
Risk factors for incidence and persistence of disability in chronic major depression and alcohol use disorders: longitudinal analyses of a population-based study
BackgroundMajor depression and alcohol use disorders are risk factors for incidence of disability. However, it is still unclear whether a chronic course of these health conditions is also prospectively associated with incidence of disability. The aim of the present study was, first, to confirm whether chronic major depression (MD) and alcohol use disorders (AUD) are, respectively, risk factors for persistence and incidence of disability in the general population; and then to analyze the role of help-seeking behavior in the course of disability among respondents with chronic MD and chronic AUD. MethodData from two assessments in the National Epidemiologic Survey on Alcohol and Related Conditions were analyzed. Disability was measured by eight domains of the Short Form 12 Health Survey version 2 (SF-12). Generalized estimating equations and logistic regression models were run to estimate risk factors for persistence and incidence of disability, respectively. ResultsAnalyses conducted on data from the US general population showed that chronic MD was the strongest risk factor for incidence and persistence of disability in the social functioning, emotional role and mental health domains. Chronic AUD were risk factors for incidence and persistence of disability in the vitality, social functioning, and emotional role domains. Within the group of chronic MD, physical comorbidity and help-seeking were associated with persistent disability in most of the SF-12 domains. Help-seeking behavior was also associated with incidence of problems in the mental health domain for the depression group. Regarding the AUD group, comorbidity with physical health problems was a strong risk factor for persistence of disability in all SF-12 domains. Help-seeking behavior was not related to either persistence or incidence of disability in the chronic alcohol group. ConclusionsChronic MD and chronic AUD are independent risk factors for persistence and incidence of disability in the US general population. People with chronic MD seek help for their problems when they experience persistent disability, whereas people with chronic AUD might not seek any help even if they are suffering from persistent disability.<br/
Magnetoelastic effects in Jahn-Teller distorted CrF and CuF studied by neutron powder diffraction
We have studied the temperature dependence of crystal and magnetic structures
of the Jahn-Teller distorted transition metal difluorides CrF and CuF
by neutron powder diffraction in the temperature range 2-280 K. The lattice
parameters and the unit cell volume show magnetoelastic effects below the
N\'eel temperature. The lattice strain due to the magnetostriction effect
couples with the square of the order parameter of the antiferromagnetic phase
transition. We also investigated the temperature dependence of the Jahn-Teller
distortion which does not show any significant effect at the antiferromagnetic
phase transition but increases linearly with increasing temperature for CrF
and remains almost independent of temperature in CuF. The magnitude of
magnetovolume effect seems to increase with the low temperature saturated
magnetic moment of the transition metal ions but the correlation is not at all
perfect
Inelastic neutron scattering study of crystal field excitations of Nd<sup>3+</sup> in NdFeAsO
Inelastic neutron scattering experiments were performed to investigate the
crystalline electric field (CEF) excitations of Nd3+ (J = 9/2) in the iron
pnictide NdFeAsO. The crystal field level structures for both the
high-temperature paramagnetic phase and the low-temperature antiferromagnetic
phase of NdFeAsO are constructed. The variation of CEF excitations of Nd3+
reflects not only the change of local symmetry but also the change of magnetic
ordered state of the Fe sublattice. By analyzing the crystal field interaction
with a crystal field Hamiltonian, the crystal field parameters are obtained. It
was found that the sign of the fourth and sixth-order crystal field parameters
change upon the magnetic phase transition at 140 K, which may be due to the
variation of exchange interactions between the 4f and conduction electrons.Comment: 5 pages, 4 figure
Deep Linear Networks can Benignly Overfit when Shallow Ones Do
We bound the excess risk of interpolating deep linear networks trained using
gradient flow. In a setting previously used to establish risk bounds for the
minimum -norm interpolant, we show that randomly initialized deep
linear networks can closely approximate or even match known bounds for the
minimum -norm interpolant. Our analysis also reveals that interpolating
deep linear models have exactly the same conditional variance as the minimum
-norm solution. Since the noise affects the excess risk only through
the conditional variance, this implies that depth does not improve the
algorithm's ability to "hide the noise". Our simulations verify that aspects of
our bounds reflect typical behavior for simple data distributions. We also find
that similar phenomena are seen in simulations with ReLU networks, although the
situation there is more nuanced
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