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, $\nu_Q$ 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 ($T_0$, $T_A$, $\bar{F}_1$) 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

Anisotropic spin-fluctuations in SmCoPO revealed by 31^P NMR measurement

31^P NMR spectral features in polycrystalline SmCoPO reveal an axially symmetric local magnetic field. At low temperature, the anisotropy of the internal magnetic field increases rapidly, with K_ab increasing faster than that of K_c. The dominant contribution to this anisotropy arises from Sm-4f electron contribution over that of Co-3d. The intrinsic width 2*(Beta) deviates from linearity with respect to bulk susceptibility below 170 K due to the enhancement of (1/T_2)dynamic, which along with the continuous increase of anisotropy in the internal magnetic field is responsible for the wipe out effect of the NMR signal, well above T_C. 1/T_1 shows large anisotropy confirming a significant contribution of Sm-4f electron spin fluctuations to 1/T_1, arising from indirect RKKY type exchange interaction indicating a non-negligible hybridization between Sm-4f orbitals and the conduction band, over the itinerant character of the Co-3d spins. This anisotropy in originates from the orientation dependence of chi"(q,omega). The 3d-spin fluctuations in the ab plane is 2D FM in nature, while along the c-axis, a signature of a weak 2D AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a field of 7 T and far above T_N is observed. The enhancement of this AFM fluctuations of the Co-3d spins along c-axis, at further low temperature is responsible to drive the system to an AFM ordered state

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

A global perspective of food market integration: A Review

Markets are important determinants of food availability and accessibility. The extent to which they make food available, accessible and keep prices stable depends on whether or not they are integrated. If markets are well integrated, it is assumed that market forces are working properly. Considering the importance of market integration in the food sector, a lot of research has been done to test integration of food markets. This paper analyses the state of the art research on food market integration, classifies it and poses questions that future research in this field can focus on. A total of 65 published articles on food market integration from all over the world were reviewed. All the reviewed papers were published between 1990 and 2014 in high quality journals. The search for literature was based on the keyword descriptor “food or commodity market integration/price transmission/price volatility” for selected databases and websites for a period ranging from 1990 to 2014. We selected the databases for keywords in titles, abstracts, keywords list and full text. The search produced thousands of papers. We then reviewed the full text of the papers, subject to relevance, in order to select the ones related to this study. Based on relevance and consideration of the time period for this study, we finally obtained 65 articles. We then classified the articles based on year of publication, country and source of study, data sampled, methodology adopted and findings and conclusions of the articles. Findings show that the majority of research has concentrated relatively more on identifying the degree of linkages among the markets but not on its implications. The paper also identified the following factors as very important in increasing/decreasing the degree of market integration: physical infrastructure, market institutions, information, competition, market power, trade, social capital, public/government intervention and export restrictions/ban. Based on these findings the paper recommends future research on food market integration to address these questions. How does the quality of physical infrastructure/roads affect the speed of adjustment of markets in case of a shock? How has popularity of mobile phone use among the farming communities affected the degree of food market integration? How does trust and networking among farmers and traders influence price transmission and market integration? What is the effect of export restrictions on price volatility and price transmission in food markets

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

Underlying Trends and International Price Transmission of Agricultural Commodities

This paper examines the extent to which increases in international food prices during the past few years have been transmitted to domestic prices in selected Asian developing countries. In analyzing the historical data, evidence on price transmission for important food commodities such as rice, wheat, and edible oil have been considered. The price transmission elasticity has been estimated using regression models coupled with recent econometric techniques such as unit root tests and error correction models with threshold adjustment. Finally, the paper draws some policy implications from the empirical results. This study provides the numerical estimates on the empirical relationship between international prices and domestic prices. The analysis uses commodity-specific monthly data rather than annual data during a period of substantial policy reforms in order to understand both long-run and short-run relationships between world and domestic prices

Trends, Persistence, and Volatility in Energy Markets

This paper makes a threefold contribution to the underlying dynamic properties and causal effects of energy prices. Firstly, the paper makes a study of the underlying trends to help identify the time series path of nonrenewable energy resources, which can have far reaching consequences for economists and policy makers alike. The analysis is extended to also determine the persistence of oil price shocks. Secondly, the study examines the causal relation between oil prices and the macroeconomy allowing for nonlinear models that have been recently advocated in the literature. Finally, this study describes the relation between oil prices and agricultural commodities. From a policy perspective, these interrelationships of agricultural and oil prices warrant careful consideration in the context of the recent energy crisis, which may very well continue in the future