53 research outputs found
Local electromagnetic properties of magnetic pnictides: A comparative study probed by NMR measurement
75As and 31P NMR studies are performed in PrCoAsO and NdCoPO respectively.
The Knight shift data in PrCoAsO indicate the presence of an antiferromagnetic
interaction between the 4f moments along the c axis in the ferromagnetic state
of Co 3d moments. We propose a possible spin structure in this system. The 75As
quadrupolar coupling constant, increases continuously with the decrease
of temperature and is found to vary linearly with the intrinsic spin
susceptibility, Kiso. This indicates a possibility of the presence of a
coupling between charge density and spin density fluctuations. Further, 31P NMR
Knight shift and spin lattice relaxation rate (1/T1) in the paramagnetic state
of NdCoPO indicate that the differences between LaCoPO and NdCoPO with SmCoPO
are due to the decrement of inter layer separation and not due to the moments
of 4f electrons. Nuclear spin lattice relaxation time (T1) in NdCoPO shows weak
anisotropy at 300 K. Using self consistent renormalization (SCR)theory of
itinerant ferromagnet, it is shown that in the ab plane, the spin fluctuations
are three dimensional ferromagnetic in nature. From SCR theory the important
spin fluctuation parameters (, , ) are evaluated. The
similarities and dissimilarities of the NMR results in As and P based systems,
with different rare earths have also been discussed.Comment: 18 pages,13 figures, accepted for publication in J. Phys. Condens.
Matte
Study of electron spin dynamics in grain aligned LaCoPO: an itinerant ferromagnet
139La NMR study was performed in grain aligned (c|| H0) sample of LaCoPO and
polycrystalline LaFePO. Knight shift is isotropic and temperature independent
in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The
spin-lattice relaxation rate in LaCoPO clearly reveals the existence of 3D spin
fluctuations both in the paramagnetic and ferromagnetic state over and above
the dominant 2D spin fluctuations in the paramagnetic state, observed earlier
from 31P NMR measurements in the same oriented sample. The spin fluctuation
parameters in LaCoPO determined from 139La NMR relaxation and magnetization
data, using the self consistent renormalization (SCR) theory, are in close
agreement and follow the universal Rhodes-Wohlfarth curve.Comment: Accepted in PR
Long-range and short-range magnetic correlations, and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3P4O14
Spin-spin correlations and microscopic origin of net magnetization in the
spin-1 trimer chain compound CaNi3P4O14 have been investigated by powder
neutron diffraction. The present study reveals a 3D long-range magnetic
ordering below 16 K where the magnetic structure consists of ferromagnetic
trimers that are coupled ferromagnetically along the spin-chain. The moment
components along the a and c axes arrange antiferromagnetically. Our study
establishes that the uncompensated moment components along the b axis result in
a net magnetization per unit cell. The magnetic structure, determined in the
present study, is in agreement with the results of recent first principles
calculation; however, it is in contrast to a fascinating experimental
prediction of ferrimagnetic ordering based on the periodicity of the exchange
interactions in CaNi3P4O14. Our study also confirms the presence of broad
diffuse magnetic scattering, due to 1D short-range spin-spin correlations, over
a wide temperature range below ~50 K down to a temperature well below the Tc.
Total neutron scattering analysis by the RMC method reveals that the dominating
spin-spin correlation above Tc is ferromagnetic and along the b axis. The
nearest neighbour spin-spin correlations along the a and c axes are found to be
weakly antiferromagnetic. The nature of the trimer spin structure of the
short-range state is similar to that of the 3D long-range ordered state. The
present investigation of microscopic nature of the magnetic ground state also
explains the condition required for the 1/3 magnetization plateau to be
observed in the trimer spin-chains. In spite of the S=1 trimer chain system,
the present compound CaNi3P4O14 is found to be a good realization of 3D magnet
below the Tc=16 K with full ordered moment values of ~2 mu_B/Ni2+ (1.98 and
1.96 mu_B/Ni2+ for two Ni sites, respectively) at 1.5 K.Comment: 10 pages, 8 figure
Crossover of the dimensionality of 3d spin fluctuations in LaCoPO
dc magnetization and 31^P spin lattice relaxation rate in the polycrystalline
sample of LaCoPO suggest a spin fluctuation dominated ferromagnetically ordered
state. Moreover, NMR data clearly indicate a crossover from 2D to 3D spin
fluctuations across T_C. In contrast to isotropic hyperfine field, H_hf at the
31^P site in LaFePO, H_hf is anisotropic in LaCoPO. The data of spin lattice
relaxation rate also exhibit anisotropic spin fluctuation. The anisotropy
vanishes near T_C
Interaction effects of region-level GDP per capita and age on labour market transition rates in Italy
Abstract The aim of this paper is to measure the effect of the interaction between age for the population of males and females aged 18 to 74 and region-level GDP per capita on labour market transition probabilities in Italy. We compare different occupational states in a sample of males and females who remained in their region of residence at two points in time (12 months apart). We estimate the transition probabilities using a flexible hierarchical logit model with interaction effects between worker age and region-level GDP per capita. We apply this model using longitudinal data from the Italian Labour Force Survey that cover the 2004–2013 period. We find empirical support for the assumption that people in the same age cohort have different labour market opportunities based on the level of GDP per capita in their region of residence. These differences are particularly relevant among younger workers
The long-run behaviour of the terms of trade between primary commodities and manufactures : a panel data approach
This paper examines the Prebisch and Singer hypothesis using a panel of twenty-four commodity prices from 1900 to 2010. The modelling approach stems from the need to meet two key concerns: (i) the presence of cross-sectional dependence among commodity prices; and (ii) the identification of potential structural breaks. To address these concerns, the Hadri and Rao (Oxf Bull Econ Stat 70:245–269, 2008) test is employed. The findings suggest that all commodity prices exhibit a structural break whose location differs across series, and that support for the Prebisch and Singer hypothesis is mixed. Once the breaks are removed from the underlying series, the persistence of commodity price shocks is shorter than that obtained in other studies using alternative methodologies.info:eu-repo/semantics/publishedVersio
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