Classical Spin Liquid State in the S=5/2 Heisenberg Kagome Antiferromagnet Li_{9}Fe_{3}(P_{2}O_{7})_{3}(PO_{4})_{2}.

We investigate the low temperature magnetic properties of a S=5/2 Heisenberg kagome 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_{N}=1.3 K and a characteristic magnetization plateau is observed at 1/3 of the saturation magnetization below T^{*}∼5 K. A moderate ^{31}P NMR line broadening reveals the development of anisotropic short-range correlations concomitantly with a gapless spin-lattice relaxation time T_{1}∼k_{B}T/ℏS, which may point to the presence of a semiclassical nematic spin-liquid state predicted for the Heisenberg kagome antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields.

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

The results of dc and ac magnetization, heat capacity, (57)Fe Mössbauer spectroscopy, dielectric, pyroelectric current and isothermal magneto-capacitance measurements of a recently reported lithium-rich layered oxide, Li3FeRuO5, related to LiCoO2-type (rhombohedral, space group R3[combining macron]m), are presented. The results reveal that the compound undergoes spin-glass freezing at 15 K. There is a peak around 34 K in pyroelectric data, which cannot be attributed to ferroelectricity, but to the phenomenon of thermally stimulated depolarization current. As revealed by magnetocapacitance data above and below the magnetic ordering temperature, magnetic and electric dipoles appear to be coupled, thereby offering evidence for magnetodielectric coupling.

Superconductivity and magnetism in K-doped EuFe(2)As(2).

Superconductivity is found in 50% K-doped EuFe(2)As(2) samples below 33 K. Our results from electrical resistivity, magnetic susceptibility and (57)Fe and (151)Eu Mössbauer spectroscopy provide clear evidence that the ordering of the Fe moments observed at 190 K in undoped EuFe(2)As(2) is completely suppressed in our 50% K-doped sample; thus there is no coexistence of the Fe magnetic order and the superconducting state. However, short range ordering of the Eu moments coexists with the superconducting state below 15 K. A bump in the susceptibility well below T(c) as well as the broadening of the Fe Mössbauer line below 27 K evidence an interplay between the Eu magnetism and the superconducting state.

Author Correction: Large spontaneous exchange bias in a weak ferromagnet Pb6Ni9(TeO6)5.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Substrate-free copper nanoclusters exhibit super diamagnetism and surface based soft ferromagnetism.

Pure metallic copper nanoparticles free of any substrate were synthesized by the thermo-chemical reduction of copper acetate using triethanolamine as a reducing-cum-protection agent. The structure and physical and magnetic properties of the Cu NPs were analysed physicochemically. Microscopic analysis reveals the formation of particles of size of 3-5 nm as seen by TEM but present as a large agglomeration as identified by SEM. A structure of Cu9 is predicted for the Cu NPs on the basis of investigations using XPS, MALDI, EPR, and magnetic measurements and supported by the prediction of DFT calculation from an earlier work. The most important findings come from magnetization studies which prove the existence of giant diamagnetism from the nanomer clusters of copper as well as the formation of two different ferromagnetic transitions at ∼40 K and ∼100 K, the latter two arising from the surface properties possibly due to thin films of CuO and/or the presence of TEOA giving rise to temperature dependent coercivity revealing them to be soft room temperature ferromagnets. The clusters of Cu NPs with the identified structure show temperature and field dependent giant diamagnetism which is about 29-39 times larger than the diamagnetism calculated from known and established atomic values. Though such enhanced diamagnetism has been predicted for noble metal clusters, experimental observation so far has been restricted to Au and Pt and this is probably the first report on substrate-free metallic copper clusters.

Pyrocurrent anomalies 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 behaviour 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 behaviour in the range 160-240 K and there are corresponding Raman mode anomalies as well in this 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 marginally with temperature. Small loss factor values validate the intrinsic behaviour of the magnetodielectric effect at room temperature.

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 (T N ) 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 |H EB| further enhances to 0.24 T under 16 T field-cooled condition, confirming the presence of large exchange bias in the material.

Comparative NMR studies on Ca3LiRuO6 and Ca3NaRuO6.

We report a comparative study of two ruthanate compounds, Ca3LiRuO6 and Ca3NaRuO6 by magnetic measurements, heat capacity and NMR. Ca3LiRuO6 is a weak ferromagnet with a magnetic ordering temperature of 115 K. The (7)Li NMR linewidth of Ca3LiRuO6 displays a broad shoulder above the magnetic ordering temperature. Anomalous shoulder of this type is observed in the susceptibility data also. The origin of these phenomena is not clear but could possibly be attributed to low dimensional magnetism. A contrasting magnetic behavior is seen in Ca3NaRuO6, an antiferromagnet with a transition temperature at 87 K. The NMR study shows that the Knight shift is proportional to the magnetic susceptibility. Also, in Ca3NaRuO6, the Knight shift and the linewidth of the spectra change differently compared to Ca3LiRuO6. The heat capacity of both compounds show a λ-type anomaly at respective magnetic transition temperatures. However, in both the systems the entropy change ([Formula: see text]S) is much less than that of an ordered S = 3/2 system.

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 80 K. 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 (χ), 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 (Ipyro) 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 cluster spin-glass dynamics. We attribute these magnetic and electric dipole anomalies to the crystallographic disorder, intrinsic to this compound.

A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field.

We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the '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 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 TN. 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.

Superconductivity at 5.2 K in ZrTe3 polycrystals and the effect of Cu and Ag intercalation.

We report the occurrence of superconductivity in polycrystalline samples of ZrTe(3) at temperature 5.2 K at ambient pressure. The superconducting state coexists with the charge density wave (CDW) phase, which sets in at 63 K. The intercalation of Cu or Ag does not have any bearing on the superconducting transition temperature but suppresses the CDW state. The feature of a CDW anomaly in these compounds is clearly seen in the DC magnetization data. Resistivity data are analyzed in order to estimate the relative loss of carriers and reduction in the nested Fermi surface area upon CDW formation in ZrTe(3) and the intercalated compounds.

Large variations in the magnetic ordering behavior of EuCu(2)As(2) with the application of external pressure and magnetic field.

The influence of external pressure on the electrical transport and magnetic properties of EuCu(2)As(2), crystallizing in a ThCr(2)Si(2)-type structure, is reported. The system is known to be an antiferromagnet below T(N) ≈ 15 K in the absence of external magnetic fields. We find that there is a gradual reduction of T(N) with the application of a magnetic field with an extrapolated value of the critical field of around 18 kOe which can drive T(N) to zero. Electrical resistivity under pressure (<11 GPa) reveals that the magnetic ordering temperature is pushed up dramatically to higher temperatures which is quite interesting if compared with the behavior in isostructural FeAs-based systems containing Eu. Above 7 GPa, the pressure-induced state appears to be ferromagnetic. The results thus reveal interesting changes in the magnetic ordering behavior of this compound with increasing pressure and magnetic fields.

Doping dependent evolution of magnetism and superconductivity in Eu(1-x)K(x)Fe2As2 (x = 0-1) and temperature dependence of the lower critical field H(c1).

We have synthesized polycrystalline samples of Eu(1-x)K(x)Fe2As2 (x = 0-1) and carried out systematic characterization using x-ray diffraction, ac and dc magnetic susceptibility, and electrical resistivity measurements. A clear signature of the coexistence of a superconducting transition (T(c) = 5.5 K) with spin density wave (SDW) ordering is observed in our underdoped sample with x = 0.15. The SDW transition disappears completely for the x = 0.3 sample and superconductivity arises below 20 K. The superconducting transition temperature Tc increases with increase in the K content and a maximum Tc = 33 K is reached for x = 0.5, beyond which it decreases again. The doping dependent Tx phase diagram is extracted from the magnetic and electrical transport data. It is found that magnetic ordering of Eu moments coexists with the superconductivity up to x = 0.6. The isothermal magnetization data taken at 2 K for the doped samples suggest the 2+ valence state of the Eu ions. We also present the temperature dependence of the lower critical field H(c1) of the superconducting polycrystalline samples. The values of H(c1)(0) obtained for x = 0.3, 0.5, and 0.7 after taking the demagnetization factor into account are 202, 330, and 212 Oe, respectively. The London penetration depth λ(T) calculated from the lower critical field does not show exponential dependence at low temperature, as would be expected for a fully gapped clean s-wave superconductor. In contrast, it shows a T2 power law feature up to T = 0.3Tc, as observed in Ba(1-x)K(x)Fe2As2 and BaFe(2-x)Co(x)As2.

Inhomogeneous magnetism in single crystalline Sr(3)CuIrO(6+delta): implications to phase-separation concepts.

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 behavior. 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 is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model on magnetic phase separation in an insulating environment.