This paper has analysed the emerging dimensions of food security and trends of crop productivity by using secondary data from 1980-81 to 2014-15 at State level of India and has also identified the impact of climatic and non-climatic variables on food security and crop productivity. The study revealed that the growth rate of foodgrains and non-foodgrains productivity was found positive except for some crops of non-foodgrains at state level with some fluctuations. In case of food security and its component, the result showed that there were wide variations across the states during the study period. The panel data regression results also highlighted that the non-climatic factors had positive and significant impact on food security except urbanization while climatic factors viz. maximum temperature had negative and significant impact and minimum temperature and rainfall had insignificant impact on food security. Furthermore, the impact of climatic and non-climatic factors had a mixed effect on crop productivity. The paper suggested that there was need to change the policy in term of building sustainable climate resilient technology, enhancing the agricultural infrastructure and optimizing use of inputs for boosting up the crop productivity and increasing public-private partnerships for sustainable development to solve the problems of food and nutrition at state level.
Structural, dielectric, ferroelectric (FE), 119Sn Mössbauer, and specific heat measurements of polycrystalline BaTi1–xSnxO3 (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and 119Sn Mössbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phase transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature based applications.
We report the evolution of structural, magnetic and dielectric properties due to partial substitution of Ba by Sr in the high temperature multiferroic YBaCuFeO 5 . This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the YBa 1-x Sr x CuFeO 5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts magnetic transition towards higher temperature whereas dielectric transition to lower temperature. These results points to the fact that magnetic and dielectric transitions get decoupled as a result of chemical pressure in form of Sr substitution. The nature of magnetodielectric coupling changes across the series with the presence of higher order coupling terms. Additionally in these compounds glassy dynamics of electric dipoles is observed at low temperatures.
The Haldane spin-chain compound, Tb2BaNiO5, has been known to order antiferromagnetically below (TN=) 63 K. The present magnetic studies on the polycrystals bring out that there is another magnetic transition at a lower temperature (T2=) 25 K, with a pronounced magnetic-field induced metamagnetic and metaelectric behavior. Multiferroic features are found below T2 only, and not at TN. The most intriguing observation is that the observed change of dielectric constant (Δε) is intrinsic and largest (e.g., ~ 18% at 15 K) within this Haldane spin-chain family, R2BaNiO5. Taking into account the fact that this trend (that is, the largest value of Δε for Tb case within this family) correlates well with a similar trend in TN (with the values of TN being ~55, 58, 53 and 32 K for Gd, Dy, Ho and Er cases), we believe that the explanation usually offered for this TN behavior in rare-earth systems is applicable for this Δε behavior as well. That is, single-ion anisotropy following crystal-field splitting is responsible for the extraordinary magnetodielectric effect in this Tb case. To our knowledge, such an observation was not made in the past literature of multiferroics.
The present work reports magnetic, magnetoelastic and magnetoelectric (ME) response of scandium (Sc) doped barium hexaferrite, BaFe10Sc2O19. DC magnetization shows that partial substitution of non-magnetic Sc for Fe in barium hexaferrite results in a reduction of Curie temperature (TC) from 730 K known for the parent compound BaFe12O19 to 430 K. Magnetization measurements show that, in BaFe10Sc2O19, in addition to the magnetic transition at 250 K corresponding to longitudinal conical magnetic structure, another magnetic anomaly occurs in the vicinity of 50 K (Tmax). Ac susceptibility and magnetic relaxation show that the magnetic transition at Tmax is associated with spin glass like dynamics. Field dependence of this glassy transition temperature follows the Almeida–Thouless (A–T) line expected for spin glass-like behaviour. Unit cell volume obtained from the neutron diffraction (ND) measurements shows deviation from the Debye–Gruneisen behaviour below 50 K, revealing the magnetoelastic coupling. Existence of magnetoelastic coupling is also confirmed by Raman spectra as Raman modes show anomalous changes around 50 K and also indicates presence of lattice modulation. Further, the magnetic structure obtained from ND data shows that incommensurate longitudinal conical ferrimagnetic structure persists from 210 K to 3 K. The integrated intensity of (0 0 2) peak and magnetic moments undergoes a subtle change below 50 K that seems to favour coexistence of long range magnetic ordering and spin glass-like dynamics. Significant magneto-dielectric effect was observed around 50 K. Temperature dependent studies of dielectric constant and pyroelectric current indicate the presence of ferroelectricity even in zero magnetic field. Further, existence of ME coupling below 50 K is confirmed by temperature dependence of pyroelectric current under magnetic fields up to 70 kOe. In short, this work identifies a new magnetic anomaly around 50 K, which is spin-glass-like inducing magnetoelastic and ME anomalies, even in the absence of external magnetic fields.
We report an unusual canted magnetism due to 3d and 4f electrons, occupying two different crystallographic sites, with its consequence to electric dipole order. This is based on neutron powder diffraction measurements on Tb2BaNiO5 (orthorhombic, Immm centrosymmetric space group), exhibiting Néel order below (TN=) 63 K, to understand multiferroic behavior below 25 K. The magnetic structure is made up of Ni and Tb magnetic moments, which are found to be mutually canted in the entire temperature range below TN, though collinearity is seen within each sublattice, as known in the past. First-principles density functional theory calculations (GCA+SO and GGA+U+SO approximations) support such a canted ground state. The intriguing finding, being reported here, is that there is a sudden increase in this Tb-Ni relative canting angle at the temperature (that is, at 25 K) at which spontaneous electric polarization sets in, with bond distance and bond angle anomalies. This finding emphasizes the need for a new spin-driven polarization mechanismthat is, a critical canting angle coupled with exchangestriction -to induce multiferroicity in magnetic insulators with canted spins.
The change in electric polarization P, plotted in Fig. 4(b), has to be multiplied by 10. This correction does not influence the interpretation and conclusion of the paper.
We report temperature dependence of dc magnetization, heat capacity, dielectric, magnetodielectric (MDE) coupling, and pyrocurrent on polycrystalline specimens resulting from a gradual dilution of Tb sublattice by Y in an exotic multiferroic Haldane spin-chain system, Tb2BaNiO5, viz., for the series Tb2−xYxBaNiO5 (x = 0.1, 0.2, 0.5, 1, and 1.5). Among various observations, the ones to be stressed are as follows: (i) The Néel temperature (TN1 = 63 K) and the second magnetic feature occurring at (TN2) 25 K get reduced to lower temperatures with increasing x in a linear fashion, with a concomitant lowering of multiferroicity onset temperature below TN2, scaling essentially with x. This finding emphasizes that local effects due to Tb play a major role on multiferroicity. Clearly, 4f dominates to determine this phenomenon—a rare finding in this field. (ii) The magnitude of the change (Δɛ′) in the dielectric constant surprisingly gets maximized for x = 0.1 with respect to that of the parent compound, attaining a relatively large value of about 22% at 15 K for a field of 100 kOe, thereby revealing that a delicate balance of nonmagnetic doping or defects in favorable cases can enhance MDE coupling. (iii) Nonmonotonic changes in Δɛ′ with a magnetic field, also a changing sign for some compositions, reveal interesting metamagnetodielectric behavior. (iv) The magnetoelectric behavior of x = 1.5 composition is found to be somewhat peculiar with respect to that of other compositions. Thus, this solid solution reveals exotic magneto(di)electric coupling anomalies.
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