Browsing by Author "M. Sawada"

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Investigation of multi-mode spin-phonon coupling and local B-site disorder in Pr2CoFeO6 by Raman spectroscopy and correlation with its electronic structure by XPS and XAS studies
(Institute of Physics Publishing, 2019) Arkadeb Pal; Surajit Ghosh; Amish G. Joshi; Shiv Kumar; Swapnil Patil; Prince K. Gupta; Prajyoti Singh; V.K. Gangwar; P. Prakash; Ranjan K. Singh; Eike F. Schwier; M. Sawada; K. Shimada; A.K. Ghosh; Amitabh Das; Sandip Chatterjee
Electronic structure of Pr2CoFeO6 (at 300 K) was investigated by x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy techniques. All three cations, i.e. Pr, Co and Fe were found to be trivalent in nature. XPS valance band analysis suggested the system to be insulating in nature. The analysis suggested that Co3+ ions exist in low spin state in the system. Moreover, Raman spectroscopy study indicated the random distribution of the B-site ions (Co/Fe) triggered by same charge states. In temperature-dependent Raman study, the relative heights of the two observed phonon modes exhibited anomalous behaviour near magnetic transition temperature TN ∼ 270 K, thus indicating towards interplay between spin and phonon degrees of freedom in the system. Furthermore, clear anomalous softening was observed below TN which confirmed the existence of strong spin-phonon coupling occurring for at least two phonon modes of the system. The line width analysis of the phonon modes essentially ruled out the role of magnetostriction effect in the observed phonon anomaly. The investigation of the lattice parameter variation across TN (obtained from the temperaturedependent neutron diffraction measurements) further confirmed the existence of the spin- phonon coupling. © 2019 IOP Publishing Ltd Printed in the UK.
Raman effect and unusual transport properties of Co-doped Mn2FeAl Heusler alloy
(Institute of Physics, 2023) Srishti Dixit; Swayangsiddha Ghosh; Neha Patel; Mohd Alam; Krishanu Bandyopadhyay; Nisha Shahi; Yogendra Kumar; M. Sawada; K. Shimada; Satyen Saha; Sanjay Singh; Sandip Chatterjee
Semiconducting materials with a distinctive blend of high electrical and low thermal conductivity are required for efficient thermoelectric devices. In this aspect, Heusler alloys are potential candidates for thermoelectric materials. It has been observed that Co doping in Mn2FeAl enhances the electrical conductivity as well as reduces the thermal conductivity of the system leading to an improvement in figure of merit. The Seebeck coefficient suggested the p-type behavior over the whole temperature range, followed by a maximum at 150 K. Additionally, the electronic properties of the suggest that the observed Raman mode is due to the electronic excitations in the system. Interestingly, this system shows a decoupling between the Seebeck coefficient and electrical conductivity, suggesting the promising potential of as a thermoelectric material and offering valuable insights into its electronic properties. Copyright © 2024 EPLA.
Roles of Re-entrant cluster glass state and spin-lattice coupling in magneto-dielectric behavior of giant dielectric double perovskite La1.8Pr0.2CoFeO6
(Institute of Physics Publishing, 2020) Prajyoti Singh; Mohd Alam; Shiv Kumar; Khyati Anand; Vinod K. Gangwar; Surajit Ghosh; M. Sawada; K. Shimada; R.K. Singh; A.K. Ghosh; Sandip Chatterjee
La based Co-Fe combined double perovskite (La1.8Pr0.2CoFeO6) was synthesized and the dielectric (zero-field and in-field), magnetic, X-ray absorption and Raman spectroscopy measurements have been investigated for La1.8Pr0.2CoFeO6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto-dielectric (MD) is found in two temperature regions (25-80 K and 125-275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin-lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view. © 2020 IOP Publishing Ltd.