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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., Comment: 7 pages, 3 figures

Motivated by the recent discovery of a semiclassical nematic spin liquid state in a Heisenberg kagom\'e 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 kagom\'e 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 $\theta \sim$ 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 $ ~${\mu}_B$ 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 ($\Delta \propto B$) 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., Comment: 10 pages, 13 figures

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., Comment: 20 pages, 12 figures, Physical Review Materials (in press)

We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$ Heisenberg kagom\'e 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 kagom\'e antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields., Comment: 6 pages, 5 figures

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.

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., Comment: 7 figures, 16 pages

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 {\alpha} 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., Comment: 9 pages, 11 figures

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., Comment: 7 pages, 8 figures

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., Comment: JMMM (in press)

We report on the synthesis of a new $\gamma$-phase of the spin $S$~=~$\frac{3}{2}$ compound SrCo$_2$(PO$_4$)$_2$ together with a detailed structural, magnetic and thermodynamic properties. The $\gamma$-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 $\gamma$-phase of SrCo$_{2}$(PO$_{4}$)$_{2}$ and they shift differently with temperature., Comment: We have suspicion that there are some experimental artifact which gone unnoticed during our measurements. Now we want re-measure and then we will again resubmit here

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., Comment: 4 figures; Physical Review B (in press)

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., Comment: 16 pages, 6 figures, 2 supplimentory figures, under revision of Scientific Reports

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., Comment: 7 figures

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., Comment: Physical Chemistry Chemical Physics, in press. arXiv admin note: text overlap with arXiv:1607.08689

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., Comment: Scientific Reports (In press), 8 figures

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., Comment: accepted in Journal of Alloys and Compounds

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., Comment: Applied Physics Letters, in press. Supplementary Material is included

We report that the spin-chain compound Dy2BaNiO5 recently proven to exhibit magnetoelectric coupling below its Neel temperature (T_N) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10K), mimicking 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at such low temperatures moves towards higher temperatures in the presence of a magnetic-field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near T_N. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure., Comment: 11 pages, 5 figueres, JPCM (Fast Track Communication), in press

We investigate the electronic structure of FeTe(0.6)Se(0.4) employing high resolution photoemission spectroscopy and ab initio band structure calculations. Fe 2p core level and the valence band spectra exhibit signature of strong electron correlation in the electronic structure. The electronic states near the Fermi level reduces in intensity with the decrease in temperature in conformity with the insulating transport observed near 300 K. The observation of an insulator to metal transition around 150 K in the transport properties may be related to the spectral lineshape change in the vicinity of the Fermi level observed in this study. The spectral features near Fermi level exhibit significant p orbital character due to the correlation induced Fe d spectral weight transfer. The experimental spectra reveal dominant temperature dependence of the spectral functions possessing large p-character. These results demonstrate significant renormalization of the character of the conduction electrons due to electron correlation and emphasizes the importance of ligand states in the superconductivity of these materials.

We report the results of various measurements, namely magnetization, complex dielectric permittivity and electric polarization (P) on Dy2BaNiO5 as a function of temperature (T) and magnetic-field (H), apart from heat-capacity (C), with the primary motivation of exploring the existence of magnetoelectric (ME) coupling among Haldane spin-chain systems. The M(T) and C(T) data establish long range magnetic ordering at 58K. The most noteworthy observations are: (i) Distinct anomalies are observed in dielectric constant ({\epsilon}') vs T and loss (tan{\delta}) vs T at different temperatures, i.e. 12.5, 30, 50 and 58K; at low temperatures, three magnetic-field-induced transitions are observed in {\epsilon}' vs H at 6, 40 and 60 kOe. These transition temperatures and critical magnetic fields track those obtained from magnetization data. This establishes the existence of strong magnetoelectric coupling in this compound. (ii) Correspondingly, electric polarization could be observed as a function of T and H in the magnetically ordered state, thereby indicating magnetism-induced ferroelectricity in this compound; this result suggests that this compound is a possible new multiferroic material among spin = 1 (nickel containing) compounds with successive magnetic transitions and strong magnetoelectric coupling., Comment: 22 pages, 5 figures Accepted in Physical Rev. B

The effect of Ni-doping on the magnetism and superconductivity in Eu0.5K0.5Fe2As2 has been studied through a systematic investigation of magnetic and superconducting properties of Eu0.5K0.5(Fe1-xNix)2As2 (x = 0, 0.03, 0.05, 0.08 and 0.12) compounds by means of dc and ac magnetic susceptibilities, electrical resistivity and specific heat measurements. Eu0.5K0.5Fe2As2 is known to exhibit superconductivity with superconducting transition temperature Tc as high as 33 K. The Ni-doping leads to a rapid decrease in Tc; Tc is reduced to 23 K with 3% Ni-doping, and 8% Ni-doping suppresses the superconductivity to below 1.8 K. In 3% Ni-doped sample Eu0.5K0.5(Fe0.97Ni0.03)2As2 superconductivity coexists with short range ordering of Eu2+ magnetic moments at Tm ~ 6 K. The suppression of superconductivity with Ni-doping is accompanied with the emergence of a long range antiferromagnetic ordering with TN = 8.5 K and 7 K for Eu0.5K0.5(Fe0.92Ni0.08)2As2 and Eu0.5K0.5(Fe0.88Ni0.12)2As2, respectively. The temperature and field dependent magnetic measurements for x = 0.08 and 0.12 samples reflect the possibility of a helical magnetic ordering of Eu2 moments. We suspect that the helimagnetism of Eu spins could be responsible for the destruction of superconductivity as has been observed in Co-doped EuFe2As2. The most striking feature seen in the resistivity data for x = 0.08 is the reappearance of the anomaly presumably due to spin density wave transition at around 60 K. This could be attributed to the compensation of holes (K-doping at Eu-site) by the electrons (Ni-doping at Fe site). The anomaly associated with spin density wave further shifts to 200 K for x = 0.12 for which the electron doping has almost compensated the holes in the system., Comment: 9 pages, 10 figures

The polycrystalline form of the compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, which was earlier believe to order antiferromagnetically below 69 K, has been recently reported by us to exhibit interesting magnetoresistance (MR) anomalies. In order to understand the magnetic anomalies of this compound better, we synthesized single crystals of this compound and subjected them to intense magnetization and MR studies. The results reveal that the magnetic behavior is strongly anisotropic as the easy axis is along a basal plane. There appear to be multiple magnetic features in the close vicinity of 70 K. In addition, there are multiple steps in isothermal magnetization (which could not be resolved in the data for polycrystalline data) for magnetic-field (H) along a basal plane. The sign of MR is positive in the magnetically ordered state, and, interestingly, the magnitude dramatically increases at the initial step for H parallel to basal plane, but decreases at subsequent steps as though the origin of these steps are different. However, for the perpendicular orientation (H || [0 0 0 1]), there is no evidence for any step either in M(H) or in MR(H). These results establish this compound is an interesting magnetic material.

We report the superconductivity at enhanced temperature of 5.2 K in the polycrystalline sample of ZrTe3 and Ni intercalated ZrTe3. ZrTe3 is a Charge Density Wave (T = 63K) compound, which is known to superconduct only below 2K in single crystalline form. We discuss that the intergrain strains in the polycrystalline samples induces an intrinsic pressure and thus enhances the transition temperature. Fe intercalation of ZrTe3 kills both the charge density wave and superconducting states, gives rise to the magnetic ordering in the compound., Comment: 2 pages. 3 figures: DAE-Solid State Physics Symposium, 2011

We report the occurrence of superconductivity in polycrystalline samples of ZrTe3 at 5.2 K temperature at ambient pressure. The superconducting state coexists with the charge density wave (CDW) phase, which sets in at 63K. The intercalation of Cu or Ag, does not have any bearing on the superconducting transition temperature but suppresses the CDW state. The feature of CDW anomaly in these compounds is clearly seen in the DC magnetization data. Resistivity data is analysed to estimate the relative loss of carriers and reduction in the nested Fermi surface area upon CDW formation in the ZrTe3 and the intercalated compounds., Comment: 5 pages, 8 figures

Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9, have been studied over a significant period of time in order to understand the unusual magnetism of ruthenium metal. However, among them, the M=Fe compound appears different since it is observed that unlike others, the 3d Fe ions and 4d Ru ions can easily exchange their crystallographic positions and as a result many possible magnetic interactions become realizable. The present study involving several experimental methods on this compound establish that the magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H ruthenates. Local structural study reveals that the possible Fe/Ru-site disorder further extends to create local chemical inhomogeneity, affecting the high temperature magnetism of this material. There is a gradual decrease of 57Fe M\"ossbauer spectral intensity with decreasing temperature (below 100 K), which reveals that there is a large spread in the magnetic ordering temperatures, corresponding to many spatially inhomogeneous regions. However, finally at about 25 K, the whole compound is found to take up a global glass-like magnetic ordering., Comment: 24 page, 7 figures

We have synthesized the polycrystalline samples of Eu1-xKxFe2As2 (x = 0-1) and carried out systematic characterization using x-ray diffraction, ac & dc magnetic susceptibility, and electrical resistivity measurements. We have seen a clear signature of the coexistence of superconducting transition (Tc = 5.5 K) with SDW ordering in our under doped sample viz. x = 0.15. The spin density wave transition observed in EuFe2As2 get completely suppressed at x = 0.3 and superconductivity arises below 20 K. Superconducting transition temperature Tc increases with increase in K content and a maximum Tc = 33 K is reached for x = 0.5, beyond which it decreases again. The doping dependent T(x) phase diagram is extracted from the magnetic and electrical transport data. It is found that magnetic ordering of Eu-moments coexists with superconductivity up to x = 0.6. The isothermal magnetization data taken at 2 K for the doped samples suggest 2+ valence states of Eu ions. We also present the temperature dependence of the lower critical field Hc1 of superconducting polycrystalline samples. The value of Hc1(0) obtained for x = 0.3, 0.5, and 0.7 after taking the demagnetization factor into account is 248, 385, and 250 Oe, respectively. The London penetration depth {\lambda}(T) calculated from the lower critical field does not show exponential behaviour at low temperature, as would be expected for a fully gapped clean s-wave superconductor. In contrast, it shows a T2 power-law feature down to T = 0.4 Tc, as observed in Ba1-xKxFe2As2 and BaFe2-xCoxAs2., Comment: 17 pages, 10 figures

We present a study of the Seebeck and Nernst coefficients of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ extended up to 28 T. The large magnitude of the Seebeck coefficient in the optimally doped sample tracks a remarkably low normalized Fermi temperature, which, like other correlated superconductors, is only one order of magnitude larger than T$_c$. We combine our data with other experimentally measured coefficients of the system to extract a set of self-consistent parameters, which identify Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ as a low-density correlated superconductor barely in the clean limit. The system is subject to strong superconducting fluctuations with a sizeable vortex Nernst signal in a wide temperature window., Comment: 4 pages including 4 figures

The flux pinning force density (Fp) of the single crystalline FeTe0.60Se0.40 superconductor has been calculated from the magnetization measurements. The normalized Fp versus h (=H/Hirr) curves are scaled using the Dew-Hughes formula to underline the pinning mechanism in the compound. The obtained values of pinning parameters p and q indicate the vortex pinning by the mixing of the surface and the point core pinning of the normal centers. The vortex phase diagram has also been drawn for the first time for the FeTe0.60Se0.40, which has very high values of critical current density Jc ~ 1.10(5) Amp/cm2 and the upper critical field Hc2(0) = 65T, with a reasonably high transition temperature Tc =14.5K., Comment: 12 pages, 4 figures

We report a comparative study of the series Fe1.1Te1-xSex and the stoichiometric FeTe1-xSex to bring out the difference in their magnetic, superconducting and electronic properties. The Fe1.1Te1-xSex series is found to be magnetic and its microscopic properties are elucidated through Moessbauer spectroscopy. The magnetic phase diagram of Fe1.1Te1-xSex is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Moessbauer spectroscopy clearly brings out the electronic differences in these two series., Comment: 6 pages, 9 figures

The transport and magnetic studies are performed on high quality FeTe0.60Se0.40 single crystals to determine the upper critical fields (Hc2), lower critical field (Hc1) and the Critical current density (Jc). The value of upper critical field Hc2 are very large, whereas the activation energy as determined from the slope of the Arrhenius plots are was found to be lower than that in the FeAs122 superconductor. The lower critical field was determined in ab direction and c direction of the crystal, and was found to have a anisotropy of 'gamma'{=(Hc1//c) / (Hc1//b)} ~ 4. The magnetic isotherms measured up to 12 Tesla shows the presence of fishtail behavior. The critical current densities at 1.8K of the single crystal was found to almost same in both ab and c direction as 1X105 Amp/cm2 in low field regime., Comment: 9 pages, 6 figures

Superconductivity is found in 50% K-doped EuFe2As2 sample below 33 K. Our results of electrical resistivity, magnetic susceptibility and 57Fe and 151Eu Mossbauer spectroscopy provide clear evidence that the ordering of the Fe moments observed at 190 K in undoped EuFe2As2 is completely suppressed in our 50% K doped sample, thus there is no coexistence between the Fe magnetic order and the superconducting state. However, short range ordering of the Eu moments is coexisting with the superconducting state below 15 K. A bump in the susceptibility well below Tc as well as a slight broadening of the Fe Mossbauer line below 15 K evidence an interplay between the Eu magnetism and the superconducting state., Comment: 7 pages, 6 figures

In the admixed Nd0.75Ho0.25Al2 system, magnetic moments of Nd and Ho occupying the same crystallographic site are antiferromagnetically coupled and the chosen stoichiometry displays a magnetic compensation behavior (Tcomp of about 24 K) in all orientations. In the vicinity of Tcomp, the conduction electron polarization (CEP) assumes the role of a soft ferromagnet exchange coupled to a pseudo-antiferromagnet comprising Nd/Ho moments, resulting in an asymmetry in the hysteretic (M-H) loop, i.e., the notion of an exchange bias field (Hexch). Across Tcomp, the CEP contribution reverses sign, and in consonance, the asymmetry in the M-H loop also undergoes a phase reversal. Interestingly, the width of the M-H loop shows a divergence, followed by a collapse on approaching Tcomp from either end. The observed behavior confirms a long standing prediction based on a phenomenological model for ferrimagnetic systems. The field induced changes across Tcomp leave an imprint of a quasi-phase transition in the heat capacity data. Magneto-resistance (\Delta R / R vs T) has an oscillatory response, in which the changes across Tc and Tcomp can be recognized., Comment: 14 text pages + 5 figures

We report anisotropic dc magnetic susceptibility $\chi(T)$, electrical resistivity $\rho(T)$, and heat capacity $C(T)$ measurements on the single crystals of CaFe$_{2-x}$Co$_x$As$_2$ for $x$ = 0 and 0.06. Large sized single crystals were grown by the high temperature solution method with Sn as the solvent. For the pure compound with $x$ = 0, a high temperature transition at 170 K is observed which is attributed to a combined spin density wave (SDW) ordering and a structural phase transition. On the other hand, for the Co-doped samples for $x$ = 0.06, the SDW transition is suppressed while superconductivity is observed at $\simeq$17 K. The superconducting transition has been confirmed from the magnetization and electrical resistivity studies. The $^{57}$Fe M\"ossbauer spectrum in CaFe$_2$As$_2$ indicates that the SDW ordering is incommensurate. In the Co-doped sample, a prominent paramagnetic line at 4.2 K is observed indicating a weakening of the SDW state., Comment: 4 pages 5 figures. Submitted to Phys. Rev. B

We predict the existence of a new ferromagnetic shape memory alloy Ga_2MnNi using density functional theory. The martensitic start temperature (T_M) is found to be approximately proportional to the stabilization energy of the martensitic phase (deltaE_tot) for different shape memory alloys. Experimental studies performed to verify the theoretical results show that Ga_2MnNi is ferromagnetic at room temperature and the T_M and T_C are 780K and 330K, respectively. Both from theory and experiment, the martensitic transition is found to be volume conserving that is indicative of shape memory behavior., Comment: 11 pages, 3 figures

We report the results of 151Eu Moessbauer effect and magnetization measurements in the Eu-doped Ca3Co2O6 and Ca3CoRhO6, which are of great current interest in the fields of spin-chain magnetism and geometrical frustration. We find that there is a pronounced increase in the line-width of the Moessbauer spectra below a certain characteristic temperature which is well-above the one at which three-diensional ordering features set in. This unusual broadening of the spectra indicates the existence of a characteristic temperature in these 'exotic' magnetic systems, attributable to the onset of incipient one-dimensional magnetic order. This is inferred from an intriguing correlation of this characteristic temperature with the paramagnetic Curie temperature (a measure of intrachain coupling strength in these cases).

Anomalous magnetic and transport properties observed in the La0.8-xEuxSr0.2MnO3 (0.04 l.e x l.e. 0.36) compounds are presented in this paper. The Curie temperature (TC) decreases from 260 K for x = 0.04 to 188 K for x = 0.16 and surprisingly thereafter increases for higher Eu concentrations (x > 0.16) and becomes nearly constant ~230 K. Resistivity increases with Eu concentration up to x = 0.16 but decreases for higher Eu concentration (x > 0.16). In the magnetoresistance data, in addition to a peak corresponding to the insulator-metal transition at (TI-M1), a second peak is also observed at a relatively lower temperature, (TI-M2). Both TI-M1 and TI-M2 follow the same trend as TC. The unique variation of TC and magnetoresistance is explained on the basis of structure and disorder correlated to microscopic electronic phase segregation. The studies with the existing studies also point to the universibility of this consideration., Comment: 9 pages, 4 figures

A negative-positive-negative switching behavior of magnetoresistance (MR) with temperature is observed in a ferromagnetic shape memory alloy Ni_1.75Mn_1.25Ga. In the austenitic phase between 300 and 120 K, MR is negative due to s-d scattering. Curiously, below 120K MR is positive, while at still lower temperatures in the martensitic phase, MR is negative again. The positive MR cannot be explained by Lorentz contribution and is related to a magnetic transition. Evidence for this is obtained from ab initio density functional theory, a decrease in magnetization and resistivity upturn at 120 K. Theory shows that a ferrimagnetic state with anti-ferromagnetic alignment between the local magnetic moments of the Mn atoms is the energetically favoured ground state. In the martensitic phase, there are two competing factors that govern the MR behavior: a dominant negative trend up to the saturation field due to the decrease of electron scattering at twin and domain boundaries; and a weaker positive trend due to the ferrimagnetic nature of the magnetic state. MR exhibits a hysteresis between heating and cooling that is related to the first order nature of the martensitic phase transition., Comment: 17 pages, 5 figures. Accepted in Phys. Rev. B

Here we report the magnetic and heat capacity studies of the double perovskite com-pounds Ba2SmRuO6 and Ba2DyRuO6. Antiferromagnetic transitions are inferred at 54 K and 47 K in Ba2SmRuO6 and Ba2DyRuO6, respectively in the magnetization measure-ments. Heat capacity measurements show large jumps at the corresponding temperatures and confirm the bulk magnetic ordering. Both the measurements provide clear indication of the ordering of the rare earth moments also along with the Ruthenium moments. How-ever, the heat capacity results suggest that the ordering of rare earth magnetic moments is spread over a large temperature range and is affected by a large crystal field effect on Ru and rare earth ions. The anomaly observed in the magnetization measurements at 42 K (below the magnetic ordering) in Ba2SmRuO6 is discerned as a reorientation of Sm3+ moments, Comment: 13pages,7fig

The rare-earth ions (RE = Eu, Dy Ho, Tm, Y) substituted charge-ordered antiferromagnetic manganites, Pr0.45RE0.05Ca0.5MnO3, were studied for the magnetic and the transport properties in the presence of external magnetic-fields of up to 14 Tesla. Regardless of the intrinsic magnetic property of RE ions, all the compounds exhibit successive step-like metamagnetic transitions at low temperatures, which are strongly correlated to their electronic transitions. At any fixed temperature in two different temperature-regimes, we observed contrary effects of the magnetic-field cycling on the resistivity of these manganites, namely, i) in the low temperature regime (<70 K), the resistivity was irreversible showing lower values than initial after a magnetic-field cycle was over, which is consistent with the irreversible magnetization, and ii) in a temperature regime above 70 K, the resistivity is irreversible with noticeably higher values than initial, whereas the magnetization was found to be reversible. For the latter case, we further show that this irreversibility of resistivity systematically depends on the temperature and the magnitude of applied magnetic-field. These results suggest that the observed resistivity behavior originated from the magnetic-field induced metamagnetic transitions and training effect., Comment: 11 pages including 1 table and 7 figures. To appear in Europhysics Letters

Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature > 450 K with a low-temperature transition from ferromagnetic to spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer indicate the presence of Fe in both valence states Fe2+ and Fe3+. We argue that the presence of Fe3+ is due to the possible hole doping in the system by cation (Zn) vacancies. In a successive ab-initio electronic structure calculation, the effects of defects (e.g. O- and Zn-vacancy) on the nature and origin of ferromagnetism are investigated for Fe-doped ZnO system. Electronic structure calculations suggest hole doping (Zn-vacancy) to be more effective to stabilize ferromagnetism in Fe doped ZnO and our results are consistent with the experimental signature of hole doping in the ferromagnetic Fe doped ZnO samples., Comment: 56 pages,16 figures. accepted for publication in Phys. Rev. B

The ABO3 type charge-ordered antiferromagnetic Nd0.50Ca0.50MnO3 (NCMO) manganite is doped at A-site by 3 % of Ba2+ for Ca2+. The resulting system, Nd0.50Ca0.47Ba0.03MnO3 (NCBMO), is studied for the effects of Ba doping on the magnetic and electronic properties. On application of magnetic field to NCBMO, strongly correlated successive sharp metamagnetic and electronic transitions are observed from antiferromagnetic-insulating to ferromagnetic-metallic state at 2.5 K. The critical magnetic field (Hc) required for metamagnetism is found to reduce drastically from 15 T for undoped NCMO to 3 T for NCBMO. On increasing the temperature, the Hc of NCBMO passes through a minimum. This behavior of Hc of NCBMO contrasts to that of NCMO. The results are discussed in context of A-site cation disorder and size.

The Eu-based compound, EuCu2As2, crystallizing in the ThCr2Si2-type tetragonal structure, has been synthesized and its magnetic behavior has been investigated by magnetization (M), heat-capacity (C) and electrical resistivity (rho) measurements as a function of temperature (T) and magnetic field (H) as well as by 151Eu Moessbauer measurements. The results reveal that Eu is divalent ordering antiferromagnetically below 15 K in the absence of magnetic field, apparently with the formation of magnetic Brillouin-zone boundary gaps. A fascinating observation is made in a narrow temperature range before antiferromagnetism sets in: That is, there is a remarkable upturn just below 20 K in the plot of magnetic susceptibility versus T even at low fields, as though the compound actually tends to order ferromagnetically. There are corresponding anomalies in the magnetocaloric effect data as well. In addition, a small application of magnetic field (around 1 kOe at 1.8 K) in the antiferromagnetic state causes spin-reorientation effect. These results suggest that there is a close balance between antiferromagnetism and ferromagnetism in this compound, Comment: Phys. Rev. B, in press

We have synthesized and investigated the magnetic and transport properties of a series of compounds, R2CoIn8 (R = rare earth). Compounds form in single phase with a tetragonal structure (space group P4/mmm, no. 162). The Ce compound shows heavy fermion behavior. The magnetic susceptibility of Pr2CoIn8 shows a marked deviation from the Curie-Weiss behavior at low temperatures, which is attributed to the crystalline electric field effects. Heat capacity and magnetization measurements show that Dy2CoIn8 undergoes a magnetic transition at 17 K and a second transition near 5 K, the latter of which may be due to spin reorientation. Magnetization of this compound shows two metamagnetic transitions approximately at 3.6 T and 8.3 T., Comment: Total 7 pages of text and figures

We report low temperature (1.8-15 K) ac magnetic susceptibility and isothermal remanent magnetization behavior for the single crystalline form of Dy2PdSi3, crystallizing in a AlB2-derived hexagonal structure, for two orientations. The results, while confirming the existence of two magnetic transitions, one at 8 K and the other at 2.5 K, as inferred from previous dc magnetization studies, suggest that the 2.5K-transition is spin-glass-like, with an interesting sensitivity to the application of an external dc magnetic field. Thus, this compound appears to undergo a transition from antiferromagnetism to spin-glass freezing as the temperature is lowered.

We report the results of ac and dc magnetic susceptibility (chi) and electrical resistivity (rho) measurements on the single crystals of Er2PdSi3, crystallizing in an AlB2-derived hexagonal structure, for two orientations H//[0001] and H//[2 -1 -1 0]. For H//[0001], there are apparently two magnetic transitions as revealed by the ac chi data, one close to 7 K attributable to antiferromagnetic ordering and the other around 2 K. However, for H // [2 -1 -1 0], we observe additional features above 7 K (near 11 and 23 K) in the plot of low-field chi(T); also, there is no corresponding anomaly in the rho(T) plot. In this respect, the magnetic behavior of this compound is novel, particularly while compared with other members of this series. The features in ac chi respond differently to the application of a small dc magnetic field for the two directions. As far as low temperature (T= 1.8 and 5 K) isothermal magnetization (M) behaviour is concerned, it exhibits meta-magnetic-like features around 2 kOe saturating at high fields for the former orientation, whereas for the latter, there is no saturation even at 120 kOe. The sign of paramagnetic Curie temperature is different for these two directions. Thus, there is a strong anisotropy in the magnetic behavior. However, interestingly, the rho(T) plots are found to be essentially isotropic, with the data revealing possible formation of magnetic superzone formation below 7 K., Comment: Physica B, in press

We report temperature dependent ac susceptibility ($\chi$) measurements on a high quality single crystal of Tb$_2$PdSi$_3$, crystallizing in a AlB$_2$-derived hexagonal structure. This compound is found to exhibit features attributable to quasi-low-dimensional magnetism at high temperatures and {\it anisotropic} spin-glass-like behavior at low temperatures ($<$ 10 K) with an unusually large frequency dependence of peak temperature in ac $\chi$(T). This compound thus presents a novel situation in {\it metallic magnetism}, considering that the former phenomenon is normally encountered only among insulators, whereas the anisotropic spin-glass-like behavior, to our knowledge, has not been known in stoichiometric intermetallic compounds., Comment: Phys. Rev. B (in press)

The single crystalline form of an insulator, Sr$_3$CuIrO$_{6+\delta}$, is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behaviour. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of "phase- separation" described for manganites [1] is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model [2] on {\it magnetic} phase separation in an insulating environment., Comment: 4 pages, 4 figures

We report the results of ac and dc magnetization (M) and heat-capacity (C) measurements on the solid solution, Sr$_3$Cu$_{1-x}$Zn$_x$IrO$_6$. While the Zn end member is known to form in a rhombohedral pseudo one-dimensional K$_4$CdCl$_6$ structure with an antiferromagnetic ordering temperature of (T$_N$ =) 19 K, the Cu end member has been reported to form in a monoclinically distorted form with a Curie temperature of (T$_C$ =) 19 K. The magnetism of the Zn compound is found to be robust to synthetic conditions and is broadly consistent with the behavior known in the literature. However, we find a lower magnetic ordering temperature (T$_o$) for our Cu compound (~ 13 K), thereby suggesting that T$_o$ is sensitive to synthetic conditions. The Cu sample appears to be in a spin-glass-like state at low temperatures, judged by a frequency dependence of ac magnetic susceptibility and a broadening of the C anomaly at the onset of magnetic ordering, in sharp contrast to earlier proposals. Small applications of magnetic field, however, drive this system to ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x = 0.75 or 0.25) significantly depress magnetic ordering; in other words, T$_o$ varies non-monotonically with x (T$_o$ ~ 6, 3 and 4 K for x = 0.25, 0.5, and 0.67 respectively). The plot of inverse susceptibility versus temperature is non-linear in the paramagnetic state as if correlations within (or among) the magnetic chains continuously vary with temperature. The results establish, Comment: 7 pages, 7 figures, Revtex

Ac and dc magnetization and heat-capacity (C) measurements performed on the pseudo-one-dimensional compound Sr$_3$CuIrO$_6$ reveal a competition between antiferromagnetic (AF) and ferromagnetic (F) exchange couplings, as evidenced by frequency dependence of ac susceptibility and by the absence of a C anomaly at the magnetic transition. The value of the saturation moment (about 0.35 $\mu_B$/formula unit) is much smaller than expected for ferromagnetism from the two S=1/2 ions (Cu and Ir). Thus, this compound is not a ferromagnet in zero magnetic field, in contrast to earlier beliefs. Of particular importance is the finding that the value of the magnetic ordering temperature is sample dependent, sensitive to synthetic conditions resulting from deviations in oxygen/Cu content. We propose that this compound serves as a unique model system to test theories on random AF-F interaction in a chain system, considering that this competition can be tuned without any chemical substitution., Comment: 8 pages, 5 figures, Revtex