Browsing by Author "A.K. Ghosh"

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A Molecular and Spectroscopic Approach to Reclamation of Coal Mine Soil Using Tree Species: a Case Study of Gevra Mining Area, Korba, India
(Springer Science and Business Media Deutschland GmbH, 2022) Preeti Singh; A.K. Ghosh; Santosh Kumar; S.L. Jat; Kumari Seema; Satya Narayana Pradhan; Manoj Kumar
Loss of topsoil and mechanical mixing of soil horizons of mining land causes depletion of huge amounts of carbon (C). Biological reclamation of the soils of mining land helps in soil organic carbon (SOC) sequestration. Therefore, to quantify the quality and quantity of soil organic carbon sequestered through biological reclamation, a chronosequence study consisting of 8- and 25-year-old reclaimed mine soil substrates planted with three different plant species, viz Azadirachta indica, Gmelina arborea and Dalbergia sissoo was undertaken at Gevra, Chhattisgarh, India. Microbial biomass carbon (MBC) and mean SOC stock were recorded highest for A. indica (1468.45 mg C kg−1 soil substrate and 334.72 Mg C ha−1 respectively) after 25 years of reclamation. All the three tree species contributed significantly in raising the non-labile SOC pool among which, the contribution of A. indica (88.25%) was found highest. SOC stock (69.82 Mg C ha−1) was found highest for topsoil substrate of 25-year-old re-vegetated site. This increase in SOC in topsoil substrate associated with a higher carbon input and the lower rates of SOC decomposition following revegetation indicated accumulation of more stable SOC forms with time. The nitrogen (N) content (r = − 0.51, p < 0.01) and C/N ratio (r = 0.56, p < 0.05) in the litter were an important controlling factor for TSOC. SOC molecules became more aromatic with a higher degree of substitution by reactive functional groups in the 25-year-old restored minesoil substrates as observed from spectroscopic analysis (E4/E6 and A253nm/A220nm). After 25 years of reclamation, similar Fourier transform infrared (FT-IR) absorption bands were observed for all tree species. However, the intensities at 1618- 1651 cm−1 in humic acid (HA) of G. arborea were higher, indicating presence of aromatic C=C, ascribed to the higher complexity of the HA fraction for G. arborea. The results indicated that spectroscopic methods (FT-IR, UV–vis, E4/E6 ratio) were clearly able to distinguish between restored minesoil substrates on the basis of the characteristics of SOC molecules and can be useful to shedding light on SOC dynamics and sequestration processes. © 2022, The Author(s) under exclusive licence to Sociedad Chilena de la Ciencia del Suelo.
A novel Raman spectroscopic approach to identify polymorphism in leflunomide: A combined experimental and theoretical study
(John Wiley and Sons Ltd, 2016) Poornima Sharma; Debraj Gangopadhyay; Sima Umrao; Shiv Kumar; A.K. Ghosh; P.C. Mishra; Ranjan K. Singh
Polymorphism is an important characteristic which affects the activity, solubility and other physical properties of a compound and can be induced by varying temperature, pressure and solvent. The presence and conversion of α to β polymorphic forms of an anti-rheumatic drug leflunomide have been studied by temperature-dependent and in situ Raman observations. Both α and β polymorphs were found to co-exist in the temperature interval 367-372 K. The α form alone exists below 367 K and the β form alone above 373 K. The C=O stretching band clearly demonstrates the α → β conversion because of breaking of N-H···O bond and formation of N-H···N bond. On cooling the Raman spectra suggest the irreversibility of this conversion. Thermodynamic stability, crystal parameters and surface morphology of both forms in the leflunomide powder used for the present study have been verified by differential scanning calorimetry, X-ray powder diffraction and scanning electron microscopy. © 2015 John Wiley & Sons, Ltd.
Agroforestry Systems: An Effective Toolfor Carbon Sequestration
(Apple Academic Press, 2024) Chandini Pradhan; A.K. Ghosh; Preeti Singh; Rajendra Gadhwal
The consequences of global warming on climate change (CC) are now evident to all. The escalating level of greenhouse gases is the root cause of global warming is the increase in greenhouse gases (GHGs). As per reports of the Intergovernmental Panel on Climate Change (IPCC) the levels of current GHG, especially CO2 have increased drastically about 30% in the atmosphere as compared to the pre-industrial levels. Such drastic increase of CO2 has occurred due to anthropogenic activities like vehicular emission due to combustion of fossil fuels, emission from industries and replacement of tropical forests by agricultural lands. In order to mitigate this hazard C-sequestration has emerged as an effective way wherein the atmospheric carbon is being converted and stored in a form that is unavailable. In terms of sequestration, plant and soil organic carbon (SOC) act as an excellent carbon sink (25% of global carbon (GC) stocks, i.e., 2,000 ± 500 Pg) and their benefits can be maximized if they are managed and manipulated in various biomes. One such option is agroforestry systems which judiciously combine the woody perennials or trees with crops, livestock, and pastures for deriving maximum ecological benefit from their interaction. The tree component in such systems serve as a long-term sink for carbon. Moreover, agroforestry systems have the ability to sequester carbon both in the aboveground andbelowground biomass portions as well as soil. It is estimated that the agroforestry systems can potentially store approximately up to 30–300 Mg C ha–1 in one meter soil depth. Thus, the chapter encapsulates brief definitions, extent, and types of agroforestry systems present across world, mechanism C-sequestration by agroforestry systems and ancillary benefits associated with them. In addition, some lights have been thrown on international policies for promoting agroforestry all of the world, their execution, loopholes, and recommendations. © 2025 by Apple Academic Press, Inc.
Anomalous ferroelectricity and strong magnetoelectric coupling in CoFe2O4-ferroelectric composites
(Elsevier Ltd, 2019) S. Shankar; Manish Kumar; A.K. Ghosh; O.P. Thakur; M. Jayasimhadri
A unique averaging mechanism is established for estimation of magnetoelectric coupling coefficient (α) by studying the effect of magnetic field on ferroelectric hysteresis loop measurements. The highest value of α obtained using this mechanism is 22 mV/cm/Oe at a field of 5000 Gauss for CoFe2O4-10%BaTiO3 (CFO-10BT) composite and is in agreement with the recent reported studies. The composites of CFO-BT exhibit interplay of magnetism, ferroelectricity and display strong magnetoelectric behaviour arising out of charge disordering. The structural studies from the combination of XRD, Raman and FTIR measurements of CFO-BT composites establishco-existence of cubic and tetragonal phase with space group. The ferroelectric studies display a low leakage charge density of 0.0031 μC/cm2 and prevalent asymmetry arising due to spatial disordering of charge distribution. Furthermore, the magnetic measurements reveal an enormous increase in the coercivity of CFO-30BT composite which is identified in terms of movement of ferromagnetic domains arising due to inclusion of trapping centres of BT in CFO. © 2018 Elsevier B.V.
Anomalous Hall effect in Cu doped Bi2Te3 topological insulator
(Institute of Physics Publishing, 2020) Abhishek Singh; Shiv Kumar; Mahima Singh; Prajyoti Singh; Rahul Singh; Vinod K Gangwar; Archana Lakhani; Swapnil Patil; Eike F Schwier; Takeshi Matsumura; K. Shimada; A.K. Ghosh; Sandip Chatterjee
The angle resolved photo-emission spectroscopy (ARPES) study and magneto-transport properties of Bi2CuxTe3-x have been investigated. ARPES study indicates the clear existence of surface states in the as-prepared samples. The estimated bandgap from ARPES is found to be ∼5 meV and 16 meV respectively for x = 0.03 and x = 0.15 samples. Presence of larger Cu concentration (x = 0.15) introduces magnetic ordering. Observed non-linearity in the Hall data is due to the existence of anomalous Hall effect which can be attributed to the 2D transport. The observed magneto-transport features might be related to the surface carriers which is confirmed by ARPES study. © 2020 IOP Publishing Ltd.
Application of VIS-NIR spectroscopy for estimation of soil organic carbon using different spectral preprocessing techniques and multivariate methods in the middle Indo-Gangetic plains of India
(Elsevier B.V., 2020) Seema; A.K. Ghosh; B.S. Das; N. Reddy
Soil organic carbon (SOC) is the main source of soil nutrients, which are essential for the growth and development of agricultural crops. Precise and quick quantification of SOC is of utmost importance in crop husbandry and soil health/carbon sequestration quantification. In order to evaluate visible and near-infrared diffuse reflectance spectroscopy (VIS-NIR) as an alternative to precise and quick method of quantification of SOC in the Indo-Gangetic plains, 280 soil samples were collected covering Inceptisols, Entisols and Alfisols and their spectra recorded. Six preprocessing techniques ((reflectance, absorbance, multiplicative scatter correction (MSC), standard normal variate (SNV), Savitzky–Golay smoothing first derivative (SG-FD) and Savitzky–Golay smoothing second derivative (SG-SD)) and four multivariate methods (partial least-squares regression (PLSR), random forest (RF), support vector regression (SVR) and multivariate adaptive regression splines (MARS)) were evaluated to predict SOC from VIS-NIR spectra. The considerable prediction accuracy and robustness were achieved using the PLSR model (RV2 = 0.73, RMSEV = 0.07, and RPDV = 1.90), RF model (RV2 = 0.69, RMSEV = 0.07, and RPDV = 1.74), SVR model (RV2 = 0.57, RMSEV = 0.08), and RPDV = 1.50), and MARS model (RV2 = 0.63, RMSEV = 0.10, and RPDV = 1.05). Findings from this study identified the reliability of SOC determinations by examining how preprocessing techniques and multivariate methods affect spectral analyses. © 2020 Elsevier B.V.
B-site disorder driven multiple-magnetic phases: Griffiths phase, re-entrant cluster glass, and exchange bias in Pr2CoFeO6
(American Institute of Physics Inc., 2019) Arkadeb Pal; Prajyoti Singh; V.K. Gangwar; Surajit Ghosh; P. Prakash; S.K. Saha; Amitabh Das; Manoranjan Kumar; A.K. Ghosh; Sandip Chatterjee
The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques. The study revealed that Pr2CoFeO6 adopted a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating antiferromagnetic ground state. Magnetization measurements revealed that the system possesses a spectrum of competing magnetic phases, viz., long range canted antiferromagnetic (AFM) spin ordering (TN ∼269 K), Griffiths-like phase, re-entrant cluster glass (TG ∼34 K), and exchange bias effects. The neutron diffraction study divulged the exhibition of a long range G-type of canted AFM spin ordering. The random nonmagnetic dilution of magnetic Fe3+ (high spin) ions by Co3+ (low spin) ions due to B-site disorder essentially played a crucial role in manifesting such magnetic properties of the system. © 2019 Author(s).
Changes in degree of phosphorus saturation and risk of P loss upon twelve years of manuring and reduced tillage
(Elsevier B.V., 2021) Satya Narayana Pradhan; A.K. Ghosh; Seema; Shankar Ram; Yogesh Pal; Chandini Pradhan
Adoption of minimum tillage and application of fertilizer integrated with farmyard manure in the long-term has been envisaged to sustain rice-based cropping systems in the Indo-Gangetic plains of India. However, substitution of mineral fertilizer based on crop N requirement results not only in increase of the total P load but also in the distribution of P fractions and soil properties that influence P adsorption. A twelve year old experiment consisting of two tillage (conventional, CT and minimum, MT tillage) and three fertilization treatments (100% inorganic fertilization, IF, 100 and 50% organic fertilization, OF) was examined to unravel the relationship between tillage and manuring effects on distribution of soil P forms vis-à-vis soil test P and how it relates to degree of P saturation (DPS). Reduced tillage intensity and organic fertilization resulted in increase of all P fractions and soluble P. Olsen-P varied from 3.4 to 59.4 mg kg−1 and was exponentially (NH4F-P/NaOH-P) or linearly (Occ-P/H2SO4-P) related to P fractions by direct or indirect effects. Increase in pH and total organic carbon coupled with increase in P load especially in OF and MT treatments resulted in decrease in the P maximum adsorption capacity (PMAC) and P bonding energy of the soil. Consequently, the degree of phosphorus saturation increased with decrease in PMAC and a change point was noted at 13.62% DPS above which soluble P increased more rapidly. Olsen P, which is used as an index of P availability, increased with reduction of tillage and organic manure addition and was closely associated with all the P fractions and DPS. The Olsen P at the change point DPS was 50.4 mg kg−1 which indicated risk of P losses and hence could be used as an index for risk assessment and identify soils that need to be managed agronomically and environmentally to avoid P losses to the environment. © 2021 Elsevier B.V.
Changes in physical properties of mine soils brought about by planting trees
(Enviro Media, 2015) Preeti Singh; Shankar Ram; A.K. Ghosh
Mining results in the formation of huge amount of overburden materials which results in soil degradation, pollution and loss of economic wealth. Reclamation of overburden soils by planting trees can stabilize the spoil and accelerate the pedogenic processes influencing soil physical, chemical and biological properties. Selected soil physical properties were studied during the reclamation of coal mine spoil under plantation and compared to reference sites to gauge the restoration of soil properties from their pristine values. Soil colour was grey in the original dump and changed to yellow brown after 25 years of reclamation. Gravel content decreased from 17.33 to 12.33% and clay content increased from 21 to 31% during the restoration process. Surface bulk density decreased with advancement of the reclamation process from 1.57 to 1.40 Mg m-3, but were wide apart from cultivated soils (1.13 Mg m-3) and natural forest (1.10 Mg m-3) of the area. Porosity of the cultivated fields (48.39%) and natural forests (50.47%) were much higher than reclamation sites (35.93%) and showed decreasing trends with increasing depth. Water holding capacity however improved from 36.48 % under fresh dump to 44.59% under 25 years of reclamation and was near to the reference sites. Thus, most of the physical properties studied, showed improved over the years of restoration under plantation indicating advancement in the pedogenic process. Hence it may be concluded that planting trees is an excellent way of restoration of coal mine overburden dumps. However it is a slow process and takes a long time to attain equilibrium with the surrounding environment. © Copyright EM International.
Characterization and classification of alluvium derived soils under different land uses in varanasi district of Uttar Pradesh
(IndianJournals.com, 2019) Seema; A.K. Ghosh
[No abstract available]
Characterization and fertility assessment of soils of chandauli district of eastern uttar pradesh for sustainable land use planning
(Indian Council of Agricultural Research, 2020) Seema; A.K. Ghosh; Sunita Yadav
Seven typical pedons representing major landforms in semi-arid and sub-tropical ecosystem of Chandauli district of Uttar Pradesh, viz. plains, mid lands and uplands developed from alluvium parent material under varying land uses were studied for their morphological characteristics, physical and chemical properties and soil classification. The colour of the soils ranged from light brown grey to brownish yellow red with a dominant hue of 10YR. These soils were acidic to moderately alkaline (pH 4.8 to 8.4) in reaction, non-saline, moderately deep to very deep and had isohyperthermic temperature and udic soil moisture regime. Texture and total organic carbon (TOC) ranged from silty loam to silty clay loam and 0.1 to 29.7 kg/ha respectively. Soils were medium in phosphorus (6.8 to 24.2 kg/ha) and available potassium (159 to 376 kg/ha ). All the pedons had ochric epipedon and underlain by cambic horizon (PI to P4) within the control section and as such they come under order Inceptisols, whereas profile 5 to profile 7 have argillic horizon so they come under order Alfisols. All soils of the study area fall in agricultural land under land capability classes III and IV having limitations of slope and erosion. On the basis of major soil constraints and potentials, suitable land use plan has been suggested. © 2020 Indian Council of Agricultural Research. All rights reserved.
Characterization and Fertility Assessment of Soils of Mirzapur District of Eastern Uttar Pradesh for Sustainable Land Use Planning
(Indian journals, 2021) Seema; A.K. Ghosh; Sunita Yadav; Preeti Singh; Aradhana Thakur
Ten typical pedons representing major landforms in semi-arid and sub-tropical ecosystem of Mirzapur district of Uttar Pradesh viz., plains, mid lands and uplands developed from alluvium parent material under varying land uses were studied for their morphological characteristics, physical and chemical properties and soil classification. The colour of the soils ranged from light brown grey to brownish yellow and dark brown with a dominant hue of 10YR. These soils were acidic to moderately alkaline (pH 6.0 to 8.6) in reaction, non-saline, moderately deep to very deep and had isohyperthermic temperature and udic soil moisture regime. Texture and total organic carbon (TOC) ranged from loam to clay loam and 0.3 to 19.9 g kg-1, respectively. Soils were lower to medium range in phosphorus (4.0 to 18.0 kg ha-1) and available potassium (96 to 299 kg ha-1). All the pedons had ochric epipedon and underlain by cambic horizon (P3, P4, P7, P8, P9 and P10) within the control section and as such they come under order Inceptisols whereas P1, P2, P5 and P6 have argillic horizon so they come under order Alfisols. All soils of the study area fall in agricultural land under land capability classes III and IV having limitations of slope and erosion. On the basis of major soil constraints and potentials, suitable land use plan has been suggested. © 2021, Indian journals. All rights reserved.
Effect of chemical pressure at the boundary of mott insulator to itinerant electron limit transition in spinel vanadates
(American Scientific Publishers, 2015) P. Shahi; A. Kumar; Rahul Singh; Ripandeep Singh; P.U. Sastry; A. Das; Amish G. Joshi; A.K. Ghosh; A. Banerjee; Sandip Chatterjee
The effect of chemical pressure on the structural, transport, magnetic and electronic properties of ZnV2O4 has been investigated by doping Mn and Co onto the Zn sites of ZnV2O4. With Mn doping the V-V distance increases and with Co doping it decreases. The resistivity and thermoelectric power data indicate that, as the V-V distance decreases, the system moves towards quantum phase transition. The transport data also indicate that the conduction is due to small polaron hopping. The chemical pressure shows a non-monotonous behaviour of charge gap and activation energy. On the other hand, when Ti is doped on the V-site of ZnV2O4, the metal-metal distance decreases and, at the same time, TN also increases. © 2015 by American Scientific Publishers.
Effect of dilution of both A-and B-sites on the multiferroic properties of spinal Mott insulators
(Institute of Physics Publishing, 2015) Prashant Shahi; Rahul K. Singh; Rajesh K. Singh; Shiv Kumar; A. Tiwari; A. Tripathi; J. Saha; S. Patnaik; A.K. Ghosh; Sandip Chatterjee
The structural, magnetic, electrical and transport properties of FeV2O4, by doping Li and Cr ions in A and B sites, respectively, have been studied. Dilution of the A site by Li doping decreases the V-V distances which in effect increases the A-V coupling. This increased coupling enhances the ferrimagnetic ordering temperature and reduces the ferroelectric transition temperature. Furthermore, since Li is non-magnetic the A-V coupling is also decreased. The increase in A-V coupling dominates over the decrease in A-V coupling with Li doping. On the other hand, Cr doping increases the ferrimagnetic ordering temperature but does not alter the ferroelectric transition temperature, which is due to the fact that the polarization originates from the presence of almost non-substituted regions. © 2015 IOP Publishing Ltd.
Effect of Pr- and Nd-doping on structural, dielectric, and magnetic properties of multiferroic Bi0.8La0.2Fe 0.9Mn0.1O3
(American Institute of Physics Inc., 2014) Rahul Singh; G.D. Dwivedi; P. Shahi; D. Kumar; Om Prakash; A.K. Ghosh; Sandip Chatterjee
Bi0.8La0.15RE0.05Fe0.9Mn 0.1O3 (where RE = Pr and Nd) have been prepared via conventional solid state route. The Rietveld refinement of X-ray diffraction patterns shows that both systems crystallize in orthorhombic Pnma space group. Raman modes observed for these two systems indicate that both systems are very close to orthorhombic Pnma structure. Appearance of prominent A1-3 and weak E-2 modes in Bi0.8La0.15Nd0.05Fe 0.9Mn0.1O3 indicate the presence of chemically more active Bi-O covalent bonds (which favors stereochemical activity of Bi lone pair electrons) in comparison to Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. Moreover, Bi 0.8La0.15Nd0.05Fe0.9Mn 0.1O3 system shows higher dielectric constant, low dielectric loss, and higher magnetization value in comparison to Bi 0.8La0.15Pr0.05Fe0.9Mn 0.1O3 system. Ferroelectric transition temperature decreases to 460 °C for both systems in comparison to 710 °C of Bi 0.8La0.2Fe0.9Mn0.1O3. The improved dielectric and magnetic response suggests Bi0.8La 0.15Nd0.05Fe0.9Mn0.1O3 a better multiferroic system than Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. © 2014 AIP Publishing LLC.
Effect of y doping on magnetic and transport properties of La 0.7Sr0.3CoO3
(2013) G.D. Dwivedi; K.K. Shukla; P. Shahi; O.K. Jha; A.K. Ghosh; A.K. Nigam; Sandip Chatterjee
The temperature variation of magnetization, resistivity and thermo electric power of undoped and Y-doped La0.7Sr0.3CoO3 samples have been investigated. Y-doping decreases the magnetization possibly due to the spin state transition of Co-ions. The low temperature conduction in (La1-yYy)0.7Sr0.3CoO3 is consistent with the variable range hopping. With Y doping, value of the Seebeck coefficient increases, as Y doping decreases bandwidth and increases distortion. © 2013 American Institute of Physics.
Effect of Y-doping on the transport and magnetic properties of La 0.5Sr0.5CoO3 and La0.7Sr 0.3CoO3
(2013) G.D. Dwivedi; K.K. Shukla; P. Shahi; A.K. Ghosh; A.K. Nigam; Sandip Chatterjee
The temperature variation of magnetization, resistivity, and thermoelectric power of undoped and Y-doped La0.7Sr0.3CoO3 and La0.5Sr0.5CoO3 samples have been investigated. Y-doping decreases the magnetization possibly due to the spin-state transition of Co ions. The low temperature conduction in (La 1-y Y y )0.7Sr0.3CoO3 is consistent with the variable range hopping. With Y-doping, value of the Seebeck coefficient increases as Y-doping decreases bandwidth and increases distortion. Seebeck coefficient value also reflects that the orbital stability increases with Sr concentration. © 2012 Springer Science+Business Media New York.
Effect of Zn doping on the magneto-caloric effect and critical constants of Mott insulator MnV2O4
(American Institute of Physics Inc., 2014) Prashant Shahi; Harishchandra Singh; A. Kumar; K.K. Shukla; A.K. Ghosh; A.K. Yadav; A.K. Nigam; Sandip Chatterjee
X-ray absorption near edge spectra (XANES) and magnetization of Zn doped MnV2O4 have been measured and from the magnetic measurement the critical exponents and magnetocaloric effect have been estimated. The XANES study indicates that Zn doping does not change the valence states in Mn and V. It has been shown that the obtained values of critical exponents β, γ and δ do not belong to universal class and the values are in between the 3D Heisenberg model and the mean field interaction model. The magnetization data follow the scaling equation and collapse into two branches indicating that the calculated critical exponents and critical temperature are unambiguous and intrinsic to the system. All the samples show large magneto-caloric effect. The second peak in magneto-caloric curve of Mn0.95Zn0.05V2O4 is due to the strong coupling between orbital and spin degrees of freedom. But 10% Zn doping reduces the residual spins on the V-V pairs resulting the decrease of coupling between orbital and spin degrees of freedom. © 2014 Author(s).
Electrical and magnetic properties of double perovskite Y2-xCaxCoMnO6 (x = 0.1, 0.2, 0.5)
(Springer, 2024) Dheeraj Kumar; Mohd Alam; Prajyoti Singh; Srishti Dixit; A.K. Ghosh; Sandip Chatterjee
The crystal structure, electronic, magnetic, and transport properties of the hole substituted (Ca2+) and partially B-site disordered double perovskite Y2-xCaxCoMnO6 system are studied. At room temperature, the samples demonstrated a monoclinic perovskite structure with a space group P21/n which was confirmed by Rietveld refinement of X-ray diffraction data. Ultra-violet visible analysis of these samples shows a direct band gap including gap energy near about 1.50 eV. X-ray photoemission spectroscopy measurement shows that component Co and Mn ions exist in a mixed state (Co3+, Co2+, Mn3+, and Mn4+). All samples exhibit semiconducting/insulating, and electrical conduction can be explained by Mott’s 3-D variable range hopping and small polaron hopping fitting. The magnetization numerical value decreases observed with increases in Ca concentration appears to be caused by increases in antiferromagnetic (AFM) phases. The double perovskite Y1.9Ca0.1CoMnO6 and Y1.8Ca0.2CoMnO6 show ferromagnetic transition at transition temperatures Tc~ 70 K and Tc~ 68 K, respectively. The analysis of the samples’ zero fields cooled DC magnetic susceptibility as a function of temperature reveals Griffiths-like singularity features that arise as the concentration of Ca increases in the parent system. The Griffith-like phase exists in the sample Y-site with Ca-substitution is independent of the structural disorder caused by the John–Teller active Mn3+ions in sample Y1.5Ca0.5CoMnO6. Field-dependent magnetization shows meta-magnetic behavior at low-temperature regions in Y1.9Ca0.1CoMnO6 and Y1.8Ca0.2CoMnO6. As the concentration of Ca increased from Y1.8Ca0.2CoMnO6 to Y1.5Ca0.5CoMnO6 meta-magnetic behavior disappeared. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.
Electronic structure by X-ray absorption spectroscopy and observation of field induced unusually slow spin relaxation from magnetic properties in pyrochlore Eu2−xFexTi2O7
(Elsevier B.V., 2019) Arkadeb Pal; Surajit Ghosh; Shiv Kumar; Eike F. Schwier; Masahiro Sawada; Kenya Shimada; Mukul Gupta; D.M. Phase; A.K. Ghosh; Sandip Chatterjee
X-ray absorption spectroscopy (XAS) and magnetization of hybrid pyrochlore Eu2-xFexTi2O7 (EFTO) were investigated, where the rare earth Eu (4f) was replaced with transition metal Fe (3d) to introduce competing 4f-3d interactions. It is confirmed that the valence states of Eu and Fe ions are formally trivalent while that of Ti ions are tetravalent (3d0). The analysis yielded that the tetravalent Ti ions occupy octahedral sites with distorted Oh symmetry which is triggered by the presence of vacant 8a anionic site adjacent to TiO6 octahedra. Further study with Fe doping revealed that it essentially reduces the octahedral distortion by introducing anionic disorder (migration of 48f oxygen ions to 8a site). Analysis of O K edge XAS spectra further confirmed the Fe substitution causing the systematic change in the ligand (O2−) coordination of the Ti4+ cations. Interestingly, a new field induced transition at low temperature T* (4 K < T* < 8 K) associated with unusually slow spin relaxation was observed. The transition shifted towards higher temperatures both with increasing applied field and Fe concentration. However, the single ion spin freezing (Tf ∼ 35 K) appears to be largely suppressed with Fe substitution. Moreover, dc magnetization data showed rise of ferromagnetic contribution below 100 K. © 2018