Browsing by Author "Ranganathan, R"

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    Complex magnetic properties associated with competing local and itinerant magnetism in Pr2Co0.86Si2.88
    (Springer Nature, 2021-06-24) Kundu, M; Pakhira, S; Choudhary, R; Paudyal, D; Lakshminarasimhan, N; Avdeev, M; Cottrell, SP; Adroja, DT; Ranganathan, R; Mazumdar, C
    Ternary intermetallic compound Pr2Co0.86Si2.88 has been synthesized in single phase and characterized by x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) analysis, magnetization, heat capacity, neutron diffraction and muon spin rotation/relaxation (μSR) measurements. The polycrystalline compound was synthesized in single phase by introducing necessary vacancies in Co/Si sites. Magnetic, heat capacity, and zero-field neutron diffraction studies reveal that the system undergoes magnetic transition below ∼4 K. Neutron diffraction measurement further reveals that the magnetic ordering is antiferromagnetic in nature with an weak ordered moment. The high temperature magnetic phase has been attributed to glassy in nature consisting of ferromagnetic clusters of itinerant (3d) Co moments as evident by the development of internal field in zero-field μSR below 50 K. The density-functional theory (DFT) calculations suggest that the low temperature magnetic transition is associated with antiferromagnetic coupling between Pr 4f and Co 3d spins. Pr moments show spin fluctuation along with unconventional orbital moment quenching due to crystal field. The evolution of the symmetry and the crystalline electric field environment of Pr-ions are also studied and compared theoretically between the elemental Pr and when it is coupled with other elements such as Co. The localized moment of Pr 4f and itinerant moment of Co 3d compete with each other below ∼20 K resulting in an unusual temperature dependence of magnetic coercivity in the system. This article is licensed under a Creative Commons Attribution 4.0 International License.
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    Large magnetic cooling power involving frustrated antiferromagnetic spin-glass state in R 2 NiSi 3 (R= Gd, Er)
    (American Physical Society, 2016-09-14) Pakhira, S; Mazumdar, C; Ranganathan, R; Giri, S; Avdeev, M
    The ternary intermetallic compounds Gd2NiSi3 and Er2NiSi3 are synthesized in chemically single phase, which are characterized using dc magnetization, ac magnetic susceptibility, heat capacity, and neutron diffraction studies. Neutron diffraction and heat capacity studies confirm that long-range magnetic ordering coexists with the frustrated glassy magnetic components for both compounds. The static and dynamical features of dc magnetization and frequency-dependent ac susceptibility data reveal that Gd2NiSi3 is a canonical spin-glass system, while Er2NiSi3 is a reentrant spin cluster-glass system. The spin freezing temperature merges with the long-range antiferromagnetic ordering temperature at 16.4 K for Gd2NiSi3. Er2NiSi3 undergoes antiferromagnetic ordering at 5.4 K, which is slightly above the spin freezing temperature at 3 K. The detailed studies of nonequilibrium dynamical behavior, viz., the memory effect and relaxation behavior using different protocols, suggest that both compounds favor the hierarchical model over the droplet model. A large magnetocaloric effect is observed for both compounds. Maximum values of isothermal entropy change (−ΔSM) and relative cooling power (RCP) are found to be 18.4 J/kg K and 525 J/kg for Gd2NiSi3 and 22.6 J/kg K and 540 J/kg for Er2NiSi3, respectively, for a change in field from 0 to 70 kOe. The values of RCP are comparable to those of the promising refrigerant materials. A correlation between large RCP and magnetic frustration is discussed for developing new magnetic refrigerant materials. ©2016 American Physical Society
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    Magnetic frustration induced large magnetocaloric effect in the absence of long range magnetic order
    (Springer Nature, 2017-08-04) Pakhira, S; Mazumdar, C; Ranganathan, R; Avdeev, M
    We have synthesized a new intermetallic compound Ho2Ni0.95Si2.95 in a single phase with a defect crystal structure. The magnetic ground state of this material found to be highly frustrated without any long range order or glassy feature as investigated through magnetic, heat capacity and neutron diffraction measurements. The interest in this material stems from the fact that despite the absence of true long range order, large magnetocaloric effect (isothermal magnetic entropy change, −ΔSM ~ 28.65 J/Kg K (~205.78 mJ/cm3 K), relative cooling power, RCP ~ 696 J/Kg (~5 J/cm3) and adiabatic temperature change, ΔT ad  ~ 9.32 K for a field change of 70 kOe) has been observed which is rather hard to find in nature. © 2017 The Authors
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    Modification of magnetic ground state in Tb2Ni0. 90Si2. 94 by thermal annealing
    (Elsevier, 2020-09-01) Pakhira, S; Bhowmik, RN; Avdeev, M; Ranganathan, R; Mazumdar, C
    In this work, we have investigated the thermal annealing effect on the physical properties of an AlB-type ternary intermetallic compound, TbNi0.90Si2.94, that undergoes spin freezing behaviour coexisting with spatially limited antiferromagnetic phase below 9.9 K in as-cast form. Thermal annealing effect is found to result in considerable changes in the magnetic ground state properties of the system. Though only one magnetic transition around 9.9 K is observed for as-cast compound, the annealed sample exhibits two distinct magnetic transitions; one around 13.5 K and another around 4 K. The magnetization measurements and zero field neutron diffraction study reveal that the high temperature transition is antiferromagnetic type, though of limited correlation length, while the low temperature transition corresponds to spin freezing behaviour. The ac susceptibility and heat capacity studies also confirm the existence of frustrated cluster glass state at lower temperature than the antiferromagnetic ordering temperature. Additionally, ac susceptibility data exhibits signature of an additional peak in the even lower temperature region (at 2.2 K for zero frequency) that tends to shift in opposite direction with frequency in contrast to that observed for conventional glassy transitions. The change in intrinsic local structural disorder of Ni and Si ions associated with annealing has been argued to be responsible for the different magnetic behaviour in as-cast and annealed samples. Published by Elsevier Ltd.
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    Spatially limited antiferromagnetic order in a cluster glass compound Tb2Ni0.90Si2.94
    (Elsevier, 2019-05-15) Pakhira, S; Mazumdar, C; Avdeev, M; Bhowmik, RN; Ranganathan, R
    In the present study, the synthesis of a new ternary intermetallic compound Tb2Ni0.90Si2.94 has been reported. The detailed studies on structure, static and dynamical magnetic properties of the compound have been investigated by means of powder x-ray diffraction, compositional analysis, dc & ac magnetization, non-equilibrium dynamics, heat capacity and neutron diffraction measurements. The dc & ac magnetic susceptibility reveal that the compound undergoes spin cluster-glass behaviour below 9.9 K. The frequency dependence of the freezing temperature have been analysed on the basis of dynamic scaling laws such as power-law divergence and Vogel-Fulcher law, which further confirm the cluster-glass state formation for the compound. A detailed study on non-equilibrium dynamical behaviour associated with cluster-glass state has been carried out through magnetic relaxation behaviour along with magnetic memory effect in zero-field-cooled (ZFC) as well as field-cooled (FC) conditions and associated aging effect. The zero-field neutron diffraction study reveals the presence of a spatially limited antiferromagnetic phase in addition to the magnetically frustrated cluster-glass state. This result has also been supported through zero-field heat capacity studies. The variation in local electronic environment among the magnetic rare-earth ions caused by the structural disorder associated with Ni/Si ions have been argued to be responsible for the coexistence of different magnetic phases. © 2019 Elsevier B.V.
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    Structural transformation in inverse-perovskite REPt3B (RE = Sm and Gd–Tm) associated with large volume reduction
    (American Chemical Society, 2017-07-05) Mondal, S; Mazumdar, C; Ranganathan, R; Avdeev, M
    In this work, we report the structural phase transformation of tetragonal inverse-perovskite REPt3B (RE = Sm, and Gd–Tm) compounds to cubic perovskite structure, with a large volume reduction of about 9% (reduction of the c axis, ∼17%; increase in the a axis, ∼5%). The structural stability of the cubic phase, however, could only be maintained by lowering the lattice parameter of the off-stoichiometric REPt3Bx (x < 1), formed in the process of annealing. The combined effect of phase transformation and stoichiometric defects is argued to be responsible for the observed volume collapse. Unexpectedly, the application of a large hydrostatic pressure of ∼20 GPa does not have any significant effect on the crystal structure. Neutron diffraction studies and heat capacity measurements unambiguously confirm different magnetic transition temperatures in the tetragonal and cubic phases. The different physical properties of these two phases demonstrate the interrelationship between the crystal chemistry and the physics of the system. The synthetic route to cubic REPt3Bx identified in this work may be utilized to prepare new ternary rare-earth intermetallics in a cubic perovksite form, which was previously found to facilitate unconventional superconductivity. © 2017 American Chemical Society