arXiv subjects

P. L. Paulose

Publications and source records attributed to P. L. Paulose.

At least 19 recordsLinked to original sources

arXiv2025

Evidence for spin liquid behavior in the frustrated three-dimensional $S = 1/2$ Heisenberg garnet NaCa$_{2}$Cu$_{2}$(VO$_{4}$)$_{3}$

Three-dimensional quantum spin liquids have remained elusive, hindered by reduced quantum fluctuations from larger lattice connectivity inherent to high-dimensional systems. Here, we investigate the remarkable persistence of dynamical short-range magnetic correlations in the nearly body-centered cubic garnet NaCa$_{2}$Cu$_{2}$(VO$_{4}$)$_{3}$ down to $T = 50$ mK, two orders of magnitude below its Curie-Weiss temperature. Using a combination of neutron and muon spectroscopies plus numerical simulations, we demonstrate that a dynamical regime emerges, characterized by a dual response in the inelastic spectrum composed of short-live dispersive excitations and a quasi-elastic component. Strongly frustrated exchange interactions combined with subtle temperature-dependent Jahn-Teller spin-lattice effects are a plausible mechanism to explain the origin of this spin-liquid behavior.

cond-mat.str-el↗

arXiv2024

Signature of point nodal superconductivity in the Dirac semimetal PdTe

Recent Angle-Resolved Photo-emission Spectroscopy (ARPES) experiments [Phys. Rev. Lett. 130, 046402 (2023)] on PdTe, a 3D-Dirac semimetal and a superconductor with the transition temperature Tc ~ 4.3 K, have revealed compelling evidence of the presence of bulk nodes in the superconducting order parameter. To investigate the validity of this proposition, here we present a detailed investigation of the magnetic field dependence of the specific heat of PdTe down to temperatures ~ 58 mK. We observed that the low temperature specific heat of PdTe with an externally applied magnetic field exhibits a power-law field dependence, a characteristic of unconventional superconductivity. Furthermore, the zero-field low-temperature electronic specific heat follows a cubic temperature dependence, which is a signature of the presence of bulk point nodes in PdTe. These intriguing observations suggest that PdTe is a rare and fascinating topological material that exhibits both Dirac semimetallic properties and superconductivity with point nodal gap symmetry.

cond-mat.supr-con↗

arXiv2023

Survival of magnetic correlations above ordering temperature in a ferromagnetically ordered classical kagomé magnet: Li9Cr3(P2O7)3(PO4)2

Motivated by the recent discovery of a semiclassical nematic spin liquid state in a Heisenberg kagomé antiferromagnet Li9Fe3(P2O7)3(PO4)2 (LFPO) with S=5/2 [Kermarrec et al. Phys. Rev. Lett. 127, 157202 (2021)], we now investigate the impact of spin quantum number S on the ground state properties by studying the isostructural kagomé magnet Li9Cr3(P2O7)3(PO4)2 (LCPO) with active t2g orbitals and S = 3/2. Thermodynamic measurements reveal that the ground state properties of LCPO is dominated by the ferromagnetic interactions with a mean-field temperature $θ\sim$ 3 K (J < 1 K) and the ordering temperature, Tc ~ 2.7 K, and the size of the ordered moment $\sim 1.05 \pm 0.25 $ ~$μ_B$ is significantly reduced from that of a fully ordered moment. The ab initio electronic structure calculations nicely corroborate the thermodynamic results and suggest the presence of additional in and out-of-plane further neighbor antiferromagnetic couplings, though significantly weaker in comparison to the dominant first-nearest neighbor ferromagnetic coupling. The spin-lattice relaxation rate measured with fields larger than the saturation field shows a magnetic field induced gap ($Δ\propto B$) in the excitation spectrum, and in $B \rightarrow 0$ limit the gap has a finite intercept ~ 3 K, equivalent to the mean-field scale. We interpret the origin of this gap is associated with the magnetic interactions inherent to the material. With our experimental results, we establish the stabilization of a ferromagnetic like ground state and the persistence of magnetic-correlations above the ordering temperature in LCPO.

cond-mat.str-el↗

arXiv2021

Classical Spin Liquid State in the $S=\frac{5}{2}$ Heisenberg Kagomé Antiferromagnet Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$

We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$ Heisenberg kagomé antiferromagnet, the layered monodiphosphate Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$, using magnetization measurements and $^{31}$P nuclear magnetic resonance. An antiferromagnetic-type order sets in at $T_{\rm N}=1.3$ K and a characteristic magnetization plateau is observed at 1/3 of the saturation magnetization below $T^* \sim 5$ K. A moderate $^{31}$P NMR line broadening reveals the development of anisotropic short-range correlations within the plateau phase concomitantly with a gapless spin-lattice relaxation time $T_1 \sim k_B T / \hbar S$, which both point to the presence of a semiclassical nematic spin liquid state predicted for the Heisenberg kagomé antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields.

cond-mat.str-el↗

arXiv2021

Competing magnetic interactions and magnetoresistance anomalies in cubic intermetallic compounds, Gd4RhAl and Tb4RhAl, and enhanced magnetocaloric effect for the Tb case

We report complex magnetic, magnetoresistance (MR) and magnetocaloric properties of Gd4RhAl and Tb4RhAl forming in the Gd4RhIn type cubic structure. Though the synthesis of the compounds was reported long ago, to our knowledge, no attempt was made to investigate the properties of these compounds. The present results of ac and dc magnetization, electrical resistivity and heat-capacity measurements down to 1.8 K establish that these compounds undergo antiferromagnetic order initially, followed by complex spin-glass features with decreasing temperature. These characteristic temperatures are: For Gd case, TN is about 46K and TG is about 21 K, and for Tb, about 32 and 28 K respectively. Additionally, there are field induced magnetic effects, interestingly leading to non-monotonic variations in MR. There is a significant MR over a wide temperature range above TN, similar to the behavior of magnetocaloric effect (MCE) as measured by isothermal entropy change (DeltaS). An intriguing finding we made is that DeltaS at the onset of magnetic order is significantly larger for the Tb compound than that observed for the Gd analogue near its TN. On the basis of this observation in a cubic material, we raise a question whether aspherical nature of the 4f orbital can play a role to enhance MCE under favorable circumstances, a clue that could be useful to find materials for magnetocaloric applications.

cond-mat.str-el↗

arXiv2021

Synthesis and magnetic properties of spin-$\frac{3}{2}$ $γ$-phase of SrCo$_{2}$(PO$_{4}$)$_{2}$ antiferromagnet

We report on the synthesis of a new $γ$-phase of the spin $S$~=~$\frac{3}{2}$ compound SrCo$_2$(PO$_4$)$_2$ together with a detailed structural, magnetic and thermodynamic properties. The $γ$-phase of SrCo$_2$(PO$_4$)$_2$ crystallizes in a triclinic crystal structure with the space group $P\bar{1}$. Susceptibility and specific heat measurements reveal that SrCo$_2$(PO$_4$)$_2$ orders antiferromagnetically below $T_{\rm N}\simeq 8.5$\,K and the nature of ordering is three dimensional (3D). The magnetic isotherm at temperatures below $T_{\rm N}$ shows a field-induced spin-flop transition, related to the magnetocrystalline anisotropy, at an applied field of $\sim$~4.5~Tesla. Remarkably, heat capacity shows magnetic-field-induced transitions at $T_{\rm N1}$ = 3.6 K and $T_{\rm N2}$ = 7.4 K. The magnetic long range ordering (LRO) is also confirmed in both the Knight shift and spin-lattice relaxation rate ($1/T_{1}$) of the $^{31}$P-NMR measurements. However, below the LRO we have not detected any NMR signal due to faster relaxation. We have detected two structurally different phosphorous sites in $γ$-phase of SrCo$_{2}$(PO$_{4}$)$_{2}$ and they shift differently with temperature.

cond-mat.str-el↗

arXiv2020

Evidence of non-trivial Berry phase and Kondo physics in SmBi

Realization of semimetals with non-trivial topologies such as Dirac and Weyl semimetals, have provided a boost in the study of these quantum materials. Presence of electron correlation makes the system even more exotic due to enhanced scattering of charge carriers, Kondo screening etc. Here, we studied the electronic properties of single crystalline, SmBi employing varied state of the art bulk measurements. Magnetization data reveals two magnetic transitions; an antiferromagnetic order with a Neel temperature of ~ 9 K and a second magnetic transition at a lower temperature (= 7 K). The electrical resistivity data shows an upturn typical of a Kondo system and the estimated Kondo temperature is found to be close to the Neel temperature. High quality of the crystal enabled us to discover signature of quantum oscillation in the magnetization data even at low magnetic field. Using a Landau level fan diagram analysis, a non-trivial Berry phase is identified for a Fermi pocket revealing the topological character in this material. These results demonstrate an unique example of the Fermiology in the antiferromagnetic state and opens up a new paradigm to explore the Dirac fermion physics in correlated topological metal via interplay of Kondo interaction, topological order and magnetism.

cond-mat.str-el↗

arXiv2020

Magnetic and transport anomalies in R2RhSi3 (R= Gd, Tb, and Dy), resembling those of an exotic magnetic skyrmion Gd2PdSi3

We have carried out magnetization, heat capacity, electrical and magnetoresistance measurements (2-300 K) for the polycrystalline form of intermetallic compounds, R2RhSi3 (R= Gd, Tb, and Dy), forming in a AlB2 derived hexagonal structure with a triangular R network. This work was primarily motivated by a revival of interest on Gd2PdSi3 after about two decades in the field of Toplogical Hall Effect due to magnetic skyrmions. We report here that these compounds are characterized by double antiferromagnetic transitions (T_N= 13.5 and 12 K for Gd, 13.5 and 6.5 K for Tb; 6.5 and 2.5 for Dy), but antiferromagnerism seems to be complex. The most notable observations common to all these compounds are: (i) There are many features in the data mimicking those seen for Gd2PdSi3, including the two field-induced changes in isothermal magnetization as though there are two metamagnetic transitions well below T_N. In view of such a resemblance of the properties, we speculate that these Rh-based materials offer a good playground to study toplogical Hall effect in a centrosymmetric structure, with its origin lying in triangular lattice of magnetic R ions; (ii) There is an increasing contribution of electronic scattering with decreasing temperature towards T_N in all cases, similar to Gd2PdSi3, thereby serving as examples for a theoretical prediction for a classical spin-liquid phase in metallic systems due to geometrical frustration.

cond-mat.str-el↗

arXiv2019

NMR, magnetization, and heat capacity studies of the uniform spin-1/2 chain compound Bi6V3O16

We report the local (NMR) and bulk (magnetization and heat capacity) properties of the vanadium-based S=1/2 uniform spin chain compound Bi6V3O16(Bi4V2O10.66). In the low-temperature α phase, the magnetic ions (V4+) are arranged in one-dimensional chains. The magnetic susceptibility shows a broad maximum around 50 K signifying a short-range magnetic order. Heat capacity measurements also reveal low-dimensional magnetism. The 51V magic angle spinning nuclear magnetic resonance measurements clearly show that the magnetic V4+ and nonmagnetic V5+ species are located on different crystallographic sites with no mixed occupation. The spin susceptibility calculated from the shift of the 51V NMR spectra reproduces the behavior observed in magnetic susceptibility and agrees well with the S=1/2 uniform spin chain model with J=113(5) K.

cond-mat.str-el↗

arXiv2019

Evolution of magnetic ordering in FeCr$_2$Se$_{4-x}$Te$_x$; $x$ = 0 -- 4.0

We have systematically studied the magnetic properties of chromium chalcogene compounds FeCr$_2$Se$_{4-x}$Te$_x$. The FeCr2Se4 undergoes antiferromagnetic ordering below 222 K. Substitution of tellurium lowers the antiferromagnetic ordering temperature and leads to short range ferromagnetic cluster behavior towards the tellurium end. Change over from antiferromagnetic to ferrimagnetic like behavior is also reflected in the corresponding transformation from semiconducting to metallic transport behavior. There is a large variation in the Curie-Weiss temperature, effective magnetic moment and ordering temperature (TN / TC) with Te substitution. The electronic band structure calculations suggest antiferromagnetic and ferrimagnetic ground state for the FeCr2Se4 and FeCr2Te4 respectively.

cond-mat.mtrl-sci↗

arXiv2019

Extraordinarily large intrinsic magnetodielectric coupling of Tb member within the Haldane spin-chain family, R2BaNiO5

The Haldane spin-chain compound, Tb2BaNiO5, has been known to order antiferromagnetically below (T_N= ) 63 K. The present magnetic studies on the polycrystals bring out that there is another magnetic transition at a lower temperature (T_2= ) 25 K, with a pronounced magnetic-field induced metamagnetic and metaelectric behavior. Multiferroic features are found below T_2 only, and not at T_N. The most intriguing observation is that the observed change of dielectric constant is intrinsic and largest (e.g., about 18% at 15 K) within this Haldane spin-chain family, R2BaNiO5. Taking into account that this trend (the largest change for Tb case within this family) correlates with a similar trend in T_N (with the values of T_N being about 55, 58, 53 and 32 K for Gd, Dy, Ho and Er cases), we believe that an explanation usually offered for this T_N behavior in rare-earth systems is applicable for this behavior as well . That is, single-ion anisotropy following crystal-field splitting is responsible for this extraordinary magnetodielectric effect in this Tb case. To our knowledge, such an observation was not made in the past literature of multiferroics.

cond-mat.str-el↗

arXiv2018

Eu valence transition behavior in the nano form of EuPd2Si2

The compound EuPd2Si2 is a well-known valence-fluctuating compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10 - 100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bulk form. To understand this microscopically, Mossbauer spectra as a function of temperature were taken. The Mossbauer spectrum of the nanocrystalline compound is essentially divalent-like at room temperature, but becomes distinctly bimodal at all temperatures below 300 K, unlike that of the bulk form. That is, there is a progressive transfer of intensity from divalent position to trivalent position with a gradual decrease of temperature. We attribute it to a first-order valence transition, with extreme broadening by defects in the nano specimen. Thus, there is a qualitative change in the valence behavior in this compound as the particle size is reduced by ball-milling. Such a particle size study is reported for the first time for a Eu-based mixed-valent compound.

cond-mat.str-el↗

arXiv2017

Large spontaneous exchange bias in a weak ferromagnet Pb6Ni9(TeO6)5

We report the magnetic and dielectric behavior of Pb6Ni9(TeO6)5, a new compound comprising the honeycomb-like layers of S=1 spins, through detailed structural, magnetic and dielectric investigation. An antiferromagnetic-type transition at 25 K (TN) with weak-ferromagnetic behavior is revealed. Interestingly, a large value of coercive field of 1.32 T at 2 K is observed. The isothermal magnetization after zero-field-cooled condition, it exhibits the presence of large spontaneous exchange bias (SEB) with a magnitude of 0.19 T at 2 K; which is rare in single bulk materials, especially without external doping. The value of |HEB| further enhances to 0.24 T under 16 T field-cooled condition, confirming the presence of large exchange bias in the material. In addition, the dielectric constant shows an anomaly at the onset of TN, indicating the presence of magnetodielectric coupling.

cond-mat.mtrl-sci↗

arXiv2017

Relaxor ferroelectric behavior and intrinsic magnetodielectric behavior near room temperature in Li2Ni2Mo3O12, a compound with distorted honeycomb and spin-chains

Keeping current interests to identify materials with intrinsic magnetodielectric behavior near room temperature and with novel pyroelectric current anomalies, we report temperature and magnetic-field dependent behavior of complex dielectric permittivity and pyroelectric current for an oxide, Li2Ni2Mo3O12, containing magnetic ions with (distorted) honey-comb and chain arrangement and ordering magnetically below 8 K. The dielectric data reveal the existence of relaxor ferroelectricity behavior in the range 160-240 K and there are corresponding Raman mode anomalies as well in that temperature range. Pyrocurrent behavior is also consistent with this interpretation, with the pyrocurrent peak-temperature interestingly correlating with the poling temperature. 7Li NMR offer an evidence for crystallographic disorder intrinsic to this compound and we therefore conclude that such a disorder is apparently responsible for the randomness of local electric field leading to relaxor ferroelectric property. Another observation of emphasis is that there is a notable decrease in the dielectric constant with the application of magnetic field to the tune of about -2.4% at 300 K, with the magnitude varying mariginally with temperature. Small loss factor values validate intrinsic behavior of the magnetodielectric effect at room temperature.

cond-mat.str-el↗

arXiv2016

Spin-glass behavior and pyroelectric anomalies in a new lithium-based oxide, Li3FeRuO5

The results of dc and ac magnetization, heat-capacity, 57Fe Moessbauer spectroscopy, dielectric, pyroelectric current and isothermal magneto-capacitance measurements on a recently reported lithium-based oxide, Li3FeRuO6, related to LiCoO2-type rhombohedral structure (space group, R-3m) are presented. The results reveal that the compound undergoes spin-glass freezing below 15 K. There is a peak around 34 K in pyroelectric data, which can not be attributed to ferroelectricity, but to the phenomenon of thermally stimulated depolarization current. As revealed by magnetocapacitance data above and below magnetic ordering temperature, magnetic and electric dipoles appear to be coupled, thereby offering evidence for magnetodielectric coupling.

cond-mat.str-el↗

arXiv2016

A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers

The area of research to discover new Li containing materials and to understand their physical properties has been of constant interest due to applications potential for rechargeable batteries. Here, we present the results of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal magnetization (M) data support ferrimagnetism, more detailed magnetic studies establish that this ferrimagnetic phase exhibits some features similar to spin-glasses. In addition, we find another broad magnetic anomaly around 40-55 K in magnetic susceptibility, attributable to cluster spin-glass phenomenon. Gradual dominance of cluster spin-glass dynamics with a decrease of temperature (T) and the apparent spread in freezing temperature suggest that the ferrimagnetism of this compound is a chaotic one. The absence of a unique freezing temperature for a crystalline material is interesting. In addition, pyroelectric current data reveals a feature in the range 40-50 K, attributable to thermally stimulated depolarization current. We hope this finding motivates future work to explore whether there is any intriguing correlation of such a feature with spin-glass dynamics. We attribute these magnetic and electric dipole anomalies to the crystallographic disorder intrinsic to this compound.

cond-mat.str-el↗

arXiv2016

Dielectric anomalies and magnetodielectric coupling behavior of single crystalline Ca3Co2O6, a geometrically frustrated magnetic spin-chain system

The dielectric behavior of the single crystals of the spin-chain system Ca3Co2O6, undergoing geometrically frustrated antiferromagnetic ordering below 25 K, has been investigated as a function of temperature and magnetic field (H) and compared with magnetization (M) behavior. The results provide evidence for anisotropic magnetodielectric (MDE) coupling in this compound. Ac susceptibility exhibits a strong frequency dependence for H parallel c with changes of this feature with the application of external dc magnetic field. No feature in ac susceptibility could be observed for H perpendicular c, thereby providing evidence for strong anisotropic spin-glass behavior. Interestingly, the strong frequency dependence in dielectric is present for both the crystallographic directions (E parallel c and E perpendicular c where E is the electric field) with a negligible influence of H, despite the existence of MDE coupling. This result appears to suggest different dynamics of electric dipole and spin-glass, although they are coupled with each other. In addition, interestingly, there is also a step at one-third of high-(magnetic) field value of MDE at some temperatures tracking a similar step in M(H). This work also confirms following unusual features reported on polycrystals, when measured along c-axis. The dielectric constant exhibits a broad peak around 50-130 K when the electric field is applied along the spin-chain (crystallographic c direction); however this feature is essentially absent for the perpendicular orientation. This finding supports the role of incipient spin-chain ordering to induce magnetodielectric coupling. There is a signature of magnetoelectric phase coexistence when the magnetic field is applied along the spin-chain irrespective of the direction of applied electric field.

cond-mat.mtrl-sci↗

arXiv2014

Anisotropic magnetodielectric coupling behavior of Ca3Co1.4Rh0.6O6 due to geometrically frustrated magnetism

We have investigated the magnetic, dielectric and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca3Co1.4Rh0.6O6, in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency dependence of ac susceptibility peak for an orientation along the spin-chain in the range 30-60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong frequency dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establishes anisotropic MDE coupling. It is intriguing to note that there is a 'step' roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.

cond-mat.str-el↗