RNRamesh Nath

Ramesh Nath

Indian Institute of Science Education and Research Thiruvananthapuram
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Ramesh Nath has a total of 357 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    Magnon Spin Current Modulation through Magnetic Ion Doping in a Compensated Iron Garnet

    by Anna Merin Francis, Murthykrishnan Panackal Balakrishnan Shailaja, Ratnamay Kolay, Ramesh Chandra Nath, Sunil Nair

    We report on the impact of manganese doping at the iron sites in Gadolinium Iron Garnet (GdIG, Gd$_{3}$Fe$_{5}$O$_{12}$), employing temperature-dependent spin Seebeck effect and ferromagnetic resonance measurements. Our findings reveal a clear shift in the magnetic compensation temperature $( T_{comp})$ in Mn-doped GdIG, with minimal changes observed in the magnetic and damping properties. Notably, the spin Seebeck signal strength was enhanced significantly with the Mn doping. This enhancement is plausibly associated with an increased spin mixing conductance and modifications in the magnon spectra, highlighting the tunability of GdIG’s spin Seebeck response and its potential for room-temperature spintronic applications.

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    Signatures of Unconventional Magnetism in the Layered Metallic Ferromagnet LaCrSb 3 From Ferromagnetic Resonance Spectroscopy

    by J. J. Abraham, S. Samanta, R. Kolay, V. Singh, R. Nath, B. Büchner, V. Kataev, A. Alfonsov

    Is a metallic ferromagnet with a layered crystal structure demonstrating intriguing electronic and magnetic properties, such as large anomalous Hall effect, strong canting of the spin lattice, and a peculiar spin‐reorientation transition. Here, we report the results of the temperature‐dependent X‐ray diffraction, static magnetization, and in particular electron spin resonance (ESR) and ferromagnetic resonance (FMR) experiments carried out over a wide range of frequencies, magnetic fields, and temperatures. Though X‐ray data reveals no structural transition down to 15 K, a strong magneto‐elastic coupling is detected across the ferromagnetic transition at K. ESR results indicate a presence of the quasi‐static short‐range correlations extending far above , which is a typical fingerprint of the low‐dimensional magnetism. The frequency‐field diagram of the FMR modes mapped below strongly suggests presence of two magnetic sublattices in . A quantitative understanding of the FMR excitations was achieved within a phenomenological model of interacting orthogonal ferro‐ and antiferromagnetic sublattices, which was earlier proposed to explain unusually strong spin canting observed by neutron diffraction [E. Granado et al., Phys. Rev.Lett. 89 , 107204 (2002)]. The FMR results corroborate this scenario and call for the development of the underlying microscopic model of unconventional magnetism in .

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    Ground-state properties of the S = 3 2 anisotropic triangular lattice antiferromagnet Na 3 Cr ( PO 4 ) 2

    by A. Magar, Sebin J. Sebastian, Q.-P. Ding, Y. Skourski, A. A. Tsirlin, Y. Furukawa, R. Nath

    We report the crystal structure and magnetic properties of a $S=\frac{3}{2}$ anisotropic triangular lattice compound ${\mathrm{Na}}_{3}\mathrm{Cr}$(${\mathrm{PO}}_{4}{)}_{2}$ employing single-crystal and powder x-ray diffraction, magnetization, heat capacity, and $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) experiments, supported by band structure calculations. Magnetic susceptibility exhibits a broad maximum at around 3.5 K, indicating the presence of a short-range antiferromagnetic order, typical of a low-dimensional spin system. Magnetization and heat capacity manifest an antiferromagnetic long-range ordering at around ${T}_{\mathrm{N}}\ensuremath{\simeq}2.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. This was further confirmed by the drastic NMR line broadening and a peak in the nuclear spin-lattice and spin-spin relaxation rates. The isothermal magnetization data exhibit a field-induced transition at around ${\ensuremath{\mu}}_{0}{H}_{\mathrm{SF}}\ensuremath{\simeq}1.7\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ reminiscent of an anisotropic two-dimensional magnet, before saturating above ${\ensuremath{\mu}}_{0}{H}_{\mathrm{sat}}\ensuremath{\simeq}4.5\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. The saturation field was further upheld by the field-dependent NMR relaxation measurements at low temperatures. The $^{31}\mathrm{P}$ NMR spectral shape confirms the commensurate antiferromagnetic nature of the ordering below ${T}_{\mathrm{N}}$. Ab initio calculations reveal a significant deformation of the triangular spin lattice, resulting in triangles with two antiferromagnetic couplings of similar strength and a much weaker coupling along the third side of the triangle.

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    Antiferromagnetic semiconductor NdAsTe: A new member of LnAsTe (Ln = Lanthanoids) compounds

    by Prabuddha Kant Kant Mishra, Sandip Guchhait, Aarti Gautam, Haribrahma Singh, Ramesh Chandra Nath, Rie Y Umetsu, Ashok Kumar Ganguli

    Rare-earth-based intermetallic compounds are at the forefront of materials science, providing valuable insights into the interplay among magnetism, topology, and structural correlations. The interesting properties of these materials, driven by localized 4f -electrons, strong spin-orbit coupling (SOC), and crystal electric field (CEF) effect, make them a focal point in solid-state physics for designing advanced functional materials. We have synthesized NdAsTe using the solid-state reaction route and explored the temperature and field-dependent magnetic properties, which demonstrate long-range antiferromagnetic (AFM) ordering below T N ≃ 2.4 K. The low-temperature Curie-Weiss temperature θ CW ≃ -1.89 K implies a net AFM interaction between the Nd 3+ ions. Furthermore, the isothermal magnetization data exhibit signatures of spin-reorientation of the AFM-aligned spins at T < T N , corroborated through magnetic entropy studies. The signature of AFM transition is also manifested as a peak at T N in the temperature-dependent specific heat which gradually shifts towards lower temperatures at higher applied fields. The derived parameters from specific heat data suggest the presence of strong electronic correlations in NdAsTe. The magnetic susceptibility and specific heat data suggest that the magnetic ground state is a Kramers' doublet with effective spin J eff = 1/2 at low temperatures. The electrical transport study revealed the semiconducting nature with a band gap of 70 meV. Furthermore, the low temperature (T < 20 K) magnetotransport studies unfold a crossover from positive to negative magnetoresistance behavior.

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    Magnetic order and spin dynamics across the ferromagnetic quantum critical point in Ni 1 − x Mo x

    by H. K. Dara, S. S. Islam, A. Magar, D. Patra, P. D. Babu, H. Luetkens, T. Shiroka, R. Nath, D. Samal

    Realizing a quantum critical point (QCP) in clean ferromagnetic (FM) metals has remained elusive due to the coupling of magnetization to the electronic soft modes that drive the transition to be of first order. However, by introducing a suitable amount of quenched disorder, one can still establish a QCP in ferromagnets. In this study, we ascertain that the itinerant ferromagnet ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Mo}}_{x}$ exhibits a FM QCP at a critical doping of ${x}_{c}\ensuremath{\simeq}0.125$. Through magnetization and muon-spin relaxation measurements, we demonstrate that the FM ordering temperature is suppressed continuously to zero at ${x}_{c}$, while the magnetic volume fraction remains $100%$ up to ${x}_{c}$, indicating a second-order phase transition. The QCP is accompanied by a non-Fermi liquid behavior, as evidenced by the logarithmic divergence of the heat capacity and the linear temperature dependence of the low-temperature resistivity. Our findings reveal a minimal effect of disorder on the critical spin dynamics of ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Mo}}_{x}$ at ${x}_{c}$, highlighting it as one of the rare systems to exhibit a clean FM QCP.

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    Magnetic and crystal electric field studies of a spin-orbit coupled hyperkagome compound Yb 3 Ga 2 Al 3 O 12

    by R. Kolay, S. Samanta, Sangeeta, M. P. Saravanan, R. Nath

    We report the magnetic properties of a ${\mathrm{Yb}}^{3+}$-based hyperkagome compound ${\mathrm{Yb}}_{3}{\mathrm{Ga}}_{2}{\mathrm{Al}}_{3}{\mathrm{O}}_{12}$ characterized via different experimental techniques and complemented by crystal electric field (CEF) calculations. The magnetic measurements suggest the absence of magnetic long-range order down to 0.1 K, and the ground state is a Kramers doublet with an effective spin ${J}_{\mathrm{eff}}=1/2$. A small Curie--Weiss temperature and magnetic scaling analysis suggest weak interaction among the magnetic ${J}_{\mathrm{eff}}=1/2$ entities. The temperature-dependent magnetic susceptibility and magnetic heat capacity could be described by a two-level Schottky function arising from the Zeeman splitting of the ground-state Kramers doublet. The CEF parameters are calculated using the point charge model. After diagonalizing the CEF Hamiltonian, we obtained the CEF energy eigenvalues and the corresponding wave functions. The simulated magnetization and heat capacity using these CEF parameters nicely reproduce our experimental data. The large separation between the ground state and the first excited state doublets in the calculated CEF scheme further supports a ${J}_{\mathrm{eff}}=1/2$ state at lower temperatures.

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    Spin-orbit-entangled frustrated magnetism in fcc Ba 2 ( Yb , Nd ) NbO 6 double perovskites

    by S. M. Hossain, Sk. Soyeb Ali, S. Mohanty, R. Kolay, M. P. Saravanan, A. K. Yogi, Y. Tokiwa, R. Nath, S. K. Panda, M. Majumder

    The search for candidate Kitaev materials has largely focused on $4d$ and $5d$ transition-metal compounds with various lattice geometries. In contrast, investigations of rare-earth $4f$ systems have thus far been restricted mainly to honeycomb and triangular lattices. In this work, we investigate the rare-earth-based double perovskites ${\mathrm{Ba}}_{2}{\mathrm{YbNbO}}_{6}$ and ${\mathrm{Ba}}_{2}{\mathrm{NdNbO}}_{6}$, which crystallize in a face-centered cubic structure. Magnetization and heat-capacity measurements establish isolated ${j}_{\mathrm{eff}}=1/2$ Kramers doublet ground states arising from strong spin-orbit coupling (SOC) and crystal electric-field effects, which are further supported by density functional theory calculations. Millikelvin-temperature thermodynamic measurements reveal long-range magnetic order with moderate frustration in both compounds. The emergence of magnetic order may be understood within an order-by-disorder scenario, as theoretically proposed for rare-earth fcc lattices with finite Kitaev interactions. Our results thus identify ${\mathrm{Ba}}_{2}{\mathrm{YbNbO}}_{6}$ and ${\mathrm{Ba}}_{2}{\mathrm{NdNbO}}_{6}$ as promising rare-earth spin-orbit-entangled magnets and motivate further experimental and theoretical investigations aimed at determining the complete exchange tensor to elucidate the microscopic origin of the underlying magnetic interactions.

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    Dynamic spin fluctuations in the S = 5 2 tetratrillium lattice antiferromagnet KBaFe 2 ( PO 4 ) 3

    by Sebin J. Sebastian, Shams Sohel Islam, R. Kolay, S. Mohanty, Q.-P. Ding, Y. Skourski, J. Sichelschmidt, M. Baenitz, Jonas A. Krieger, T. J. Hicken, et al.

    The three-dimensional (3D) magnet ${\mathrm{KBaFe}}_{2}$(${\mathrm{PO}}_{4}{)}_{3}$ hosts an effective tetratrillium spin lattice of ${\mathrm{Fe}}^{3+}$ ($S=5\text{/}2$) ions, offering a prototypical platform to study frustration-driven phenomena in 3D. Through magnetization, specific heat, $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR), and muon spin relaxation ($\textmu{}\mathrm{SR}$) experiments, supported by first-principles calculations, we uncover an unconventional ground state. Despite strong antiferromagnetic interactions with a large Curie-Weiss temperature ${\ensuremath{\theta}}_{\mathrm{CW}}=\ensuremath{-}70(2)\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, no magnetic long-range order is observed down to 30 mK. Below ${T}^{*}\ensuremath{\simeq}3.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the NMR linewidth becomes nearly field independent and the spin-spin relaxation rate $1/{T}_{2}$ saturates, accompanied by a two-component relaxation in the transverse nuclear magnetization ${M}_{xy}$. The latter indicates the emergence of short-range dynamical correlations, which was further corroborated by a robust and field-insensitive broad maximum in specific heat. In $\textmu{}\mathrm{SR}$, we detect neither a static internal field nor spin freezing; instead, the spins remain dynamic down to 30 mK and the asymmetry curves are best described by two coexisting dynamic relaxation channels: a dominant fast (sporadic) channel and a slower Markovian component. Their differing weights and fluctuation rates suggest microscopic inhomogeneity in spin dynamics. These persistent low-temperature spin fluctuations are found to be intrinsic to the 3D frustrated tetratrillium geometry, exemplifying ${\mathrm{KBaFe}}_{2}$(${\mathrm{PO}}_{4}{)}_{3}$, a rare 3D antiferromagnet with a classical spin that fosters unconventional dynamics.

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    Crystal electric field excitations and spin dynamics in the spin-orbit coupled distorted honeycomb magnet BiErGeO 5

    by S. Mohanty, S. Guchhait, S. S. Islam, Surya P. Patra, M. P. Saravanan, J. A. Krieger, T. J. Hicken, H. Luetkens, D. T. Adroja, Gøran J. Nilsen, et al.

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    Frustration-driven magnetic correlations in the spin- 5 2 triangular lattice antiferromagnet RbFe ( HPO 3 ) 2

    by V. Nagpal, Sebin J. Sebastian, Surya P. Patra, S. Shibash, Q.-P. Ding, Y. Furukawa, R. Nath

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